HomeMy WebLinkAboutSP2. Floodplains
Commission Memorandum
REPORT TO: Honorable Mayor and City Commission
FROM: Craig Woolard, Public Works Director
Brian Heaston, Senior Engineer
SUBJECT: Progress update on issues raised by City Commission during the policy discussion on January 25, 2016 concerning floodplain development and draft FEMA floodplain maps for Bozeman Creek and tributaries.
MEETING DATE: April 4, 2016
AGENDA ITEM TYPE: Special Presentation
BACKGROUND: This memo provides a progress update on issues raised by the City Commission during the policy discussion on floodplain development and the draft FEMA floodplain maps for Bozeman Creek and tributaries. Staff is providing this update as a special
presentation and is not requesting any action be taken by the Commission at this time. However,
we welcome Commission discussion and direction as we continue to work through policy issues
surrounding FEMA floodplains. The city regulates development in FEMA floodplains depicted on Flood Insurance Rate Maps
(FIRMs) officially adopted by city ordinance. The officially adopted FIRMs for Bozeman Creek
and tributaries are outdated and inaccurate but serve as the effective regulatory product
nonetheless. FEMA has completed draft floodplains maps which – until final maps are produced – are the best available data concerning flood hazards for Bozeman Creek and tributaries. Final
floodplain maps are tentatively scheduled to be released in the fall of 2017 pending completion
of FEMA’s public appeal and comment process for the draft maps. The city will have 6 months
to officially adopt the final maps by ordinance once they are released which places final adoption
on a tentative timeline for spring of 2018.
During the January 25 policy discussion the following four staff recommendations were
presented to the City Commission. Information addressing questions and issues raised by the
City Commission during the policy discussion surrounding these recommendations are provided
below.
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Staff Recommendations Presented on January 25, 2016
1) Maximize the protection of public health, safety, and welfare by immediately recognizing
the draft floodplain maps for regulatory purposes during the interim period until official map adoption.
2) Create redevelopment flexibility by immediately removing the local limitation that
residential structures in floodplains be elevated on fill and thereby allow elevating to
occur by other means.
3) Modify immediately the City’s local floodplain variance procedures to reflect federal and
state requirements in the model floodplain ordinance.
4) Endorse the working group process to update the City’s floodplain regulations.
Issues/Questions Raised by City Commission on January 25, 2016 and Staff Responses
A. Notice to property owners in the draft FEMA floodplain must occur and happen prior to
recognizing the draft FEMA floodplain for regulatory purposes over the interim period. On April 7, 2016, from 5p – 8p in the City Commission meeting room, the city is jointly
hosting a Public Open House with Gallatin County and DNRC regarding the draft FEMA
floodplain maps for Bozeman Creek and tributaries. The open house provides an opportunity for property owners to review the draft floodplain areas and have their questions and concerns addressed one-on-one by city and DNRC staff, or Gallatin County staff for properties in the county. Nearly 600 individual property owners
(includes condominium owners) within the city own property in the draft 100-year FEMA
floodplain. A postcard (attached) was directly mailed on March 25 to notify each of these owners of the proposed floodplain changes and the open house. A media alert with a fact sheet for the mapping project and open house will be sent to local print and TV media outlets in advance of the open house to garner general community attention.
An interactive floodplain map viewer has been prepared by the city’s GIS Department and serves as a primary public engagement tool. The map web address, www.bozeman.net/maps, is referenced on the open house postcard. The map viewer
shows the draft FEMA floodplains, proposed map changes, and the existing floodplain
areas. Hyperlinks to one-page PDF briefs are provided within the map viewer when a
flood zone is selected. The briefs (attached) contain relevant information about owning property in the selected flood zone; particularly, development regulations and insurance requirements.
B. City floodplain regulations require new or substantially improved structures in the FEMA
floodplain to be elevated 2’ above the base flood elevation on fill extending 15’ beyond
the foundation wall. What means are allowable under State rules for elevating structures beyond elevating on fill?
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The 2014 state model floodplain regulations provided with the January 25, 2016 meeting
packet address minimum federal and state requirements for regulating development in
the floodplain. The model ordinance states: “Elevation of the Lowest Floor – Elevating the lowest floor may be by either
suitable fill, foundation wall enclosure, stem walls, pilings, posts, piers, columns,
or other acceptable means; (MCA 76-5-402(2)(b), 44 CFR 60.3(b)(8), 44 CFR
60.3(c)(6))” The other means listed in the model ordinance for elevating the structure are more
practicable to achieve in an urban environment than the currently limited elevating on
fill requirement in the city’s regulations. FEMA technical guidance for elevating
structures via various means is attached and provides figures and descriptions for accomplishing the elevation standard (Chapter 5E - Elevation, FEMA Guide P-259, Engineering Principles and Practices for Retrofitting Flood-Prone Residential Structures
(Third Ed.), Jan 2012).
C. What is the variance process and criteria set forth in the current city floodplain
regulations and what is the variance process and criteria set forth in the state model floodplain ordinance?
Current floodplain regulations utilize the zoning variance process and criteria utilized in
the greater Unified Development Code, Chapter 38 of Bozeman Municipal Code. These criteria are attached and do contain specific criteria for floodplain variances (38.35.060.C.4 BMC). Variance criteria from the state model ordinance are also
attached and are generally similar to the existing variance criteria in BMC with one
notable exception dealing with floodplain variances for historic structures. The state
model ordinance at Section 12.4.2 reflects federal floodplain variance language at 44 CFR 60.6(a) allowing a variance “…for the repair or rehabilitation of historic structures upon a determination that the proposed repair or rehabilitation will not preclude the
structure’s continued designation as a historic structure and the variance is the minimum
necessary to preserve the historic character and design of the structure.”
D. What is the timeframe for state model ordinance adoption?
Formal adoption by the city of final FEMA floodplain maps for regulatory purposes must
occur by ordinance. The final floodplain maps are anticipated to be complete in late
2017. Once the final maps are delivered to the city it will have 6-months to adopt the maps by ordinance, putting the final ordinance adoption on a timeline for early 2018. The content of the model ordinance will require revision to fit within the city’s overall
development code structure and modifications to the model ordinance are likely. The
model ordinance review/modification process will occur in coordination with DNRC and
FEMA and will kick off later this year.
E. How do the floodplain regulations treat renovation of historic structures in the FEMA
floodplain?
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The current floodplain regulations require substantial improvements to historic
residential structures be elevated 2’ above the base flood elevation on fill. For historic commercial structures, such as those found in the downtown core, the structure must be elevated or floodproofed 2’ above the base flood elevation. Floodproofing requirements
apply to the HVAC, plumbing, and electrical systems of the building. The model
ordinance provides more detail regarding floodproofing than the city’s current
floodplain regulations. Furthermore, the model ordinance contains specific variance criteria for historic structures that are generally more lenient than typical floodplain variance criteria if the structure is designated as historic by the U.S. Secretary of Interior
or by the city’s local historic preservation program.
F. How does the draft FEMA floodplain appeal process work?
The draft FEMA floodplain areas may be challenged during the formal 90-day Appeal
and Comment Period of the floodplain map development process. That process is
projected to begin winter 2017 upon FEMA’s release of preliminary flood insurance rate
maps depicting the draft floodplain areas. An information sheet is attached which provides a general overview of the appeal process and timeline. Appeals to the floodplains require supporting technical documentation showing why a particular
floodplain area is incorrect and should be amended. Technical materials for appealing a
floodway area will require detailed and rigorous engineering hydraulic modeling
analysis. Appeal information for floodplain areas outside of the proposed floodway don’t necessarily require modeling and may be resolved utilizing other techniques such as a site specific topographic survey or preparation of an Elevation Certificate for an existing
building. If, for instance, an existing structure is located in the proposed floodplain and
a topographic survey were provided showing the ground level adjacent to the structure is
in fact higher than the proposed base flood elevation, then that should constitute a reasonable factual basis for amending the proposed floodplain map to remove the structure from the floodplain when the final floodplain maps are issued.
G. Notice to property owners that are mapped out of the floodplain on the draft FEMA
floodplain maps must occur.
The postcard notices mailed March 25 were limited to property owners with property in
the draft FEMA floodplain. Notice to property owners newly mapped out of the
floodplain with the draft maps is proposed to occur when the preliminary flood insurance
rate maps are produced unless directed otherwise.
H. If the draft FEMA floodplains are recognized for regulatory purposes during the interim
period then properties mapped outside of the draft FEMA floodplain, but inside the
officially adopted FEMA floodplain, should be relieved of the regulatory burden.
FEMA requires the city to enforce floodplain regulations meeting the minimum requirements of 44 CFR 60.3 in order for it to remain a community in good standing with
the National Flood Insurance Program and thus have flood insurance available to
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property owners in the city. Selectively abdicating regulatory requirements for
properties currently mapped into the adopted floodplain, but out of the draft floodplain,
would constitute a violation of 44 CFR 60.3 and subject the city to probation or suspension from the NFIP pursuant to 44 CFR 59.24(b) and (c).
If the city recognizes the draft FEMA floodplains for regulatory purposes, it is required
nevertheless to continue regulating development within the adopted FEMA floodplains.
In those areas where the draft and adopted floodplains overlap, the more restrictive floodplain area or higher base flood elevation would apply. The requirement to carry flood insurance on federally backed mortgages in the floodplain only applies to buildings
located in the adopted FEMA floodplain and does not apply to buildings located in the
draft FEMA floodplain.
I. What is the benefit/cost of participating in the National Flood Insurance Program and administering floodplain regulations that result in restricted development rights in the
FEMA floodplain versus the benefit/cost of not participating in the NFIP?
Unknown. Should the City Commission be interested in expending the time and monetary resources necessary to hire qualified professionals to perform an economic analysis then direction to staff must be provided.
UNRESOLVED ISSUES: Since January 25 staff has met with several organizations and
community groups interested in the draft FEMA floodplain maps. During meetings with the
Downtown BID and TIF boards questions surrounding the potential for Mill Ditch to be utilized as a downtown flood mitigation facility were raised. The draft floodplain area downtown is
expansive, due in part to reduced flow moving down Mill Ditch in the draft hydraulic model
when compared to the existing effective model. Water in Mill Ditch is diverted from Bozeman
Creek and forms the “stream” at the base of Peet’s Hill that moves through the Library property
and Lindley Park before discharging to the East Gallatin River north of the Interstate. Conceptually, Mill Ditch could serve as a flood control bypass facility for the downtown area.
An evaluation of the capacity of the ditch to serve this purpose must be performed, however,
which will require engineering analysis and manipulation of the FEMA hydraulic model to
understand how the respective floodplains of Bozeman Creek and Mill Ditch would change if
more floodwater is directed from one to the other. The results of the evaluation would inform decisions on whether to pursue a potential flood hazard mitigation project. To perform this
evaluation, the Engineering Division has placed $20k in the proposed FY17 budget and will be
issuing an RFP to select a qualified engineering firm to perform this work in the near future. The
$20k would also fund an overall evaluation of the FEMA hydraulic model to identify potential
problem areas in the draft mapping for the city to bring forward during the formal appeal period.
Recognizing the draft FEMA floodplains for regulatory purposes remains unresolved. To do so
would take formal Commission action to amend the current floodplain regulations by expanding
their applicability to sources of best available data such as that provided with the draft maps.
Should the Commission express a willingness to regulate the draft floodplain areas Staff will prepare an ordinance to amend the floodplain regulations. We suggest that the effective date of
the ordinance coincide with the release of preliminary flood insurance rate maps on track for this
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coming fall. To meet this timeframe for effectiveness a hearing on first read of the ordinance
would be necessary in July or August. The ordinance would limit its scope to the applicability
expansion to best available data, allowing other forms of elevating buildings aside from elevating
on fill, and incorporating the historic structure variance criteria in the state model ordinance. This ordinance would serve as a stop gap measure while a wholesale update to the city’s
floodplain regulations is prepared over the interim period utilizing the state model ordinance as
its foundation.
ALTERNATIVES: As Suggested by the Commission. FISCAL EFFECTS: Not included with this Special Presentation.
Attachments: Property owner notification postcard
Flood zone briefs hyperlinked to interactive floodplain web map Chapter 5E - Elevation, FEMA Guide P-259, Engineering Principles and Practices
for Retrofitting Flood-Prone Residential Structures (Third Ed.), Jan 2012
City’s current floodplain variance criteria
State model ordinance floodplain variance criteria
Map appeal information sheet
Report compiled on March 28, 2016
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FLOOD INSURANCE RATE MAP UPDATES
The City of Bozeman is currently working with FEMA and Montana
DNRC to update Flood Insurance Rate Maps for Bozeman Creek and its
tributaries. You are receiving this postcard because proposed
floodplain changes could affect your property.
Visit the City’s website above to view maps showing proposed
floodplain changes and to get more information about this project.
PUBLIC OPEN HOUSE
April 7, 2016 | 5:00PM - 8:00PM | Bozeman City Commission Room
Bozeman City Hall, 121 N Rouse Ave, Bozeman, MT 59715
This open house is intended for property owners on or near Bozeman
Creek and its tributaries. It is being run in conjunction with Gallatin
County. Please drop by the Open House at any time to:
Speak with City or DNRC Staff one-on-one about how Flood
Insurance Rate Map changes could affect your property.
Hear a short, informational presentation about the overall
Floodplain Mapping Project at 5:15PM, 6:15PM, or 7:15PM.
We look forward to seeing you there!
ATTENTION
BOZEMAN PROPERTY OWNERS
in or near a FLOODPLAIN
www.bozeman.net/maps
Please contact us directly for more information.
Brian Heaston
Bozeman City Engineering
bheaston@bozeman.net
406.582.2280
Tiffany Lyden
MT DNRC
tlyden@mt.gov
406.444.0599 78
If you own a building in an area that will be newly mapped into a
100-Year Floodplain (including Floodway), contact your lender as
early as possible to start the discussion about flood insurance.
A lender must require flood insurance when a building carrying a federally
backed loan is located in a mapped 100-Year Floodplain (including Floodway), unless it can be proven that the
building is actually above the flood elevation or outside of the floodplain.
Periodically, lenders will review their loans to reassess flood risk based on the best available data. Updates to
Flood Insurance Rate Maps will typically trigger a periodic review. Some property owners may not see any
insurance changes with this mapping update.
INSURANCE REQUIREMENT
City of Bozeman
FLOOD INSURANCE RATE MAP UPDATES
Promoting flood-risk awareness
A FLOODWAY is the area within a 100-Year Floodplain that must be kept free from new development
so that the 100-Year Flood (1% Annual Chance Flood, Base Flood) can be carried without substantial
increases in flood heights. The Floodway will usually see the highest water velocities and deepest
inundation during a 100-Year Flood event.
DEVELOPMENT REGULATIONS
The City of Bozeman strictly regulates development in Floodways
to protect human life and property by ensuring that there are no
increases in upstream flood elevations.
In accordance with the City’s Floodplain Regulations:
New building construction is not permitted in the Floodway.
Improvement to existing structures in a Floodway must obtain a Floodplain Development Permit.
Draft floodplain maps for Bozeman Creek and its tributary streams are going through the review process and are
not yet effective. Until these maps become effective, the City strongly encourages proposed construction projects to
utilize draft map data to ensure that property development methods will minimize flood damage. Draft map data
also provides an opportunity to develop smarter and thereby reduce potentially high costs of flood insurance
premiums.
It is important to discuss the City’s Floodplain Regulations with City staff to understand the impacts of Flood
Insurance Rate Map updates on proposed construction projects in a mapped floodplain, especially if portion of the
project site is located in a Floodway.
Owning property in a FLOODWAY
A lender must require flood
insurance when a building
carrying a federally backed
loan is located in a mapped
100-Year Floodplain.
The City strongly
encourages proposed
construction projects to utilize
draft map data to ensure that
development methods will
minimize flood damage.
Brian Heaston
Bozeman City Engineering
bheaston@bozeman.net 406.582.2280
Tiffany Lyden
MT Dept of Natural Resources and Conservation
tlyden@mt.gov 406.444.0599 79
City of Bozeman
FLOOD INSURANCE RATE MAP UPDATES
Promoting flood-risk awareness
Brian Heaston
Bozeman City Engineering
bheaston@bozeman.net 406.582.2280
Tiffany Lyden
MT Dept of Natural Resources and Conservation
tlyden@mt.gov 406.444.0599
If you own a building in an area that will be newly mapped into a 100-Year
Floodplain, contact your lender as early as possible to start the discussion
about flood insurance.
A lender must require flood insurance when a building carrying a federally backed
loan is located in a mapped 100-Year Floodplain, unless it can be proven that the
building is actually above the flood elevation or outside of the floodplain. Periodically, lenders will review their
loans to reassess flood risk based on the best available data. Updates to Flood Insurance Rate Maps will typically
trigger a periodic review.
Some property owners may not see any insurance changes with this mapping update. For buildings that will be
newly mapped into the floodplain, a lender may require flood insurance and/or elevation documentation. Buildings
in newly mapped areas are eligible for subsidized premiums as long as flood insurance is purchased within
11 months of the date the new Flood Insurance Rate Maps become effective (estimated for 2018).
INSURANCE REQUIREMENT A lender must require
flood insurance when a
building carrying a
federally backed loan is
located in a mapped
100-Year Floodplain.
A 100-YEAR FLOODPLAIN (1% Annual Chance Floodplain) is an area that will be inundated by a 100-Year
Flood, a flood event having a 1% chance of being equaled or exceeded in any given year. The 100-Year Flood
is also referred to as a 1% Annual Chance Flood or a Base Flood.
DEVELOPMENT REGULATIONS
The City of Bozeman requires Floodplain Development Permits
for development in the 100-Year Floodplain (1% Annual Chance
Floodplain) to protect human life and property.
In accordance with the City’s Floodplain Regulations:
New building construction must obtain a Floodplain Development Permit.
New residential construction must be elevated 2 feet above the 100-Year Flood (Base Flood) Elevation.
New commercial construction must be floodproofed or elevated 2 feet above the 100-Year Flood
(Base Flood) Elevation.
Improvements to existing structures must obtain a Floodplain Development Permit. Improvements to an
existing structure greater than 50% of a structure’s market value (a Substantial Improvement) require the
entire structure to be brought into compliance with the City’s Floodplain Regulations.
Development may be restricted by City Zoning Regulations.
Draft floodplain maps for Bozeman Creek and its tributary streams are going through review and are not yet
effective. Until these maps become effective, the City strongly encourages proposed construction projects to utilize
draft map data to ensure that property development methods will minimize flood damage. Draft map data also
provides an opportunity to develop smarter and reduce potentially high costs of flood insurance premiums.
It is important to discuss the City’s Floodplain Regulations with City staff to understand the impacts of Flood
Insurance Rate Map updates on proposed construction projects in a mapped floodplain.
Owning property in a 100-YEAR FLOODPLAIN
The City strongly
encourages proposed
construction projects to use
draft map data to ensure that
development methods will
minimize flood damage.
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City of Bozeman
FLOOD INSURANCE RATE MAP UPDATES
Promoting flood-risk awareness
Owning property in a 500-YEAR FLOODPLAIN
If you own a building in a 500-Year Floodplain (0.2% Annual Chance
Floodplain), you are at a moderate risk of flooding under the National Flood
Insurance Program. It is recommended that you purchase flood insurance
even if your lender does not require you to do so.
A lender must require flood insurance when a building carrying a federally backed
loan is located in a 100-Year Floodplain (1% Annual Chance Floodplain). A lender does not need to require flood
insurance when a building carrying a federally backed loan is located outside of a 100-Year Floodplain due to a
decreased flood risk. A lender may still require flood insurance, however, if a building is located in a 500-Year
Floodplain in order to protect their investment.
Periodically, lenders will review their loans to reassess flood risk based on the best available data. Updates to
Flood Insurance Rate Maps will typically trigger a periodic review. Regardless of where your property is located,
your lender may require flood insurance and/or elevation documentation for a building.
Some property owners may not see any insurance changes with this mapping update. Buildings located in areas
that will be newly mapped into the 100-Year Floodplain are eligible for subsidized premiums as long as flood
insurance is purchased within 11 months of the date the new Flood Insurance Rate Maps become effective
(estimated for 2018).
INSURANCE REQUIREMENT Lenders can require flood
insurance for a building
they are financing,
regardless of where the
building is located.
A 500-YEAR FLOODPLAIN (0.2% Annual Chance Floodplain) is an area that will be inundated by a
500-Year Flood, a flood event having a 0.2% chance of being equaled or exceeded in any given year.
The 500-Year Flood is also referred to as a 0.2% Annual Chance Flood.
DEVELOPMENT REGULATIONS
The City of Bozeman’s Floodplain Regulations do not regulate
development in the 500-Year Floodplain (0.2% Annual Chance
Floodplain) although flooding is still possible in this area.
New construction and building improvement may occur in the 500-Year
Floodplain without a Floodplain Development Permit. Zoning may be restricted
by the City’s Zoning Regulations.
If your property has areas of both 100-Year and 500-Year Floodplain, development may require a Floodplain
Development Permit, depending on exactly where the development will occur. It is important to discuss the
location of any development with City staff to understand the impacts of the City’s Floodplain Regulations and Flood
Insurance Rate Map updates on proposed projects in or near a mapped 100-Year Floodplain.
Unlike in a 100-Year
Floodplain, a Floodplain
Development Permit is not
required for development
in a 500-Year Floodplain.
Brian Heaston
Bozeman City Engineering
bheaston@bozeman.net 406.582.2280
Tiffany Lyden
MT Dept of Natural Resources and Conservation
tlyden@mt.gov 406.444.0599 81
5E-1ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
ENGINEERING PRINCIPLES AND PRACTICES
5EElevation
One of the most common of all retrofitting techniques is to
raise an entire existing superstructure above the DFE. When
properly done, the elevation of a house places the living area
above all but the most severe floods.
The steps required for elevating a building are essentially the
same in all cases. A cradle of steel beams is inserted under (or
through) the structure; jacks are used to raise both the beams
and structure to the desired height; a new, elevated foundation
for the house is constructed; utility systems are extended and
modified; and the structure is lowered back onto the new
foundation and reconnected.
While the same basic elevation techniques are used in all
situations, the final siting and appearance of the house will
depend on the final elevation and type of foundation used.
However, the actual elevation process is only a small part of
the whole operation in terms of planning, time, and expense.
The most critical steps involve the preparation of the house
for elevation and the construction of a new, adequately designed, and elevated foundation. The elevation
process becomes even more complex with added weight, height, or complex design or shape of the house.
Brick or stucco veneers may require removal prior to elevation. Building additions may need to be elevated
independently from the main structure.
NOTE
FEMA strongly encourages that
flood retrofits provide protection
to the DFE (or BFE plus 1 foot,
whichever is higher). However,
in some situations, lower
flood-protection levels may be
appropriate. Homeowners and
design professionals should
meet with a local building official
to discuss the selected retrofit
measure and the elevation to
which it will protect the home.
The text and examples in this
manual assume flood protection
measures will be implemented to
the DFE.
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5E-2 ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
5E ELEVATION
5E.1 Types of Residential Structures that Can Be Elevated
The elevation of houses over a crawlspace; houses with basements; houses on piers, columns, or piles; and
houses on a slab-on-grade are examined here. In each of these situations, the designer must account for
multiple (non-flood-related) hazards, such as wind and seismic
forces. The various methods utilized to elevate different home
types are illustrated in the pages that follow, providing the
designer with an introduction to the design of these measures.
Houses that are elevated using solid foundation walls as opposed
to piers, columns, or piles to raise the finished floor to or above
the DFE must include openings to allow the automatic entry
and exit of floodwater. Guidance on the design and installation
of flood vents can be found in Section 5E.1.2.1.
5E.1.1 Houses Over a Crawlspace
These are generally the easiest and least expensive houses to
elevate. They are usually one- or two-story houses built on a
masonry crawlspace wall. This allows for access in placing the
steel beams under the house for lifting. The added benefit is
that, since most crawlspaces have low clearance, most utilities
(heat pumps, water heaters, air conditioners, etc.) are not
placed under the home; thus the need to relocate utilities may
be limited. Houses over a crawlspace can be:
elevated on extended solid foundation walls (see Figures
5E-1 through 5E-5); or
elevated on an open foundation such as masonry piers (see Figures
5E-6 through 5E-8).
NOTE
Figures 5E-1 through 5E-5
illustrate the elevation of a home
on extended solid foundation
walls. Subsequent figures for
various elevation techniques will
include only those illustrations
unique to that technique.
CROSS REFERENCE
Information on the design of
foun dation wall openings and
adjust ment of existing utility
systems can be found in
Chapter 5W.
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5E-3ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
ELEVATION 5E
Figure 5E-1.
Existing wood-frame
house on crawlspace
foundation to be elevated
with extended walls and
piers
Figure 5E-2.
Step 1 of elevating an
existing wood-frame
house on extended
foundation walls and
piers: Install network of
steel I-beams
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5E-4 ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
5E ELEVATION
Figure 5E-3.
Step 2 of elevating an
existing wood-frame
house on extended
foundation walls and
piers: Lift house and
extend foundation walls
and piers (reinforce
as needed); relocate
utility and mechanical
equipment above flood
level
Figure 5E-4.
Step 3 of elevating an
existing wood-frame
house on extended
foundation walls and
piers: Set house on new
extended foundation and
remove I-beams
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5E-5ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
ELEVATION 5E
Figure 5E-5.
Cross-section of elevated
wood-frame house on
extended piers and
crawlspace walls
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5E-6 ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
5E ELEVATION
Figure 5E-6.
Step 1 of elevating
an existing wood
frame house on new
or extended pier
foundations: Install
network of steel I-beams.
Step 2 (not shown): Lift
house, rebuilding or
extending (reinforce as
needed) piers; relocate
utility and mechanical
equipment above flood
level.
Figure 5E-7.
Step 3 of elevating
an existing wood-
frame house on new or
extended pier foundation:
Set house on new or
extended piers
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5E-7ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
ELEVATION 5E
Figure 5E-8.
Cross-section of
elevated wood-
frame house on new
or extended pier
foundation
88
5E-8 ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
5E ELEVATION
5E.1.2 Houses Over Basements
These houses are slightly more difficult to elevate because their
mechanical and HVAC equipment is usually in the basement.
In addition, basement walls may already have been extended
to the point where they cannot structurally withstand flood
forces. Houses over basements can be:
elevated on solid foundation walls by creating a new
masonry-enclosed area on top of an abandoned and filled-
in basement (see Figures 5E-9 and 5E-10); or
elevated on an open foundation, such as masonry piers, by
filling in the old basement (see Figures 5E-11 and 5E-12).
CROSS REFERENCE
FEMA’s post- and pre-FIRM
re quirements do not allow
basements below the BFE for
substantially damaged/improved
and post-FIRM applications.
For more information on what
retrofitting measures are
allowable under FEMA guidelines,
refer to Chapter 2, Regulatory
Requirements.
Figure 5E-9.
Elevated wood-frame
house with new masonry-
enclosed area on top of
an abandoned and filled-
in basement; utility and
mechanical equipment
must be relocated above
the flood level
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5E-9ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
ELEVATION 5E
Figure 5E-10.
Cross-section of elevated
wood-frame house with
extended masonry-
enclosed area on top of
an abandoned and filled-
in basement
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5E-10 ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
5E ELEVATION
Figure 5E-11.
Cross-section of elevated
wood-frame house on
new reinforced piers on
top of the existing filled-
in basement
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5E-11ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
ELEVATION 5E
Figure 5E-12.
Elevated wood-frame
house set on new
reinforced piers on top
of the existing filled-in
basement
Figure 5E-13. Typical opening for solid foundation wall
5E.1.2.1 Design of Openings in Foundation Walls for Intentional Flooding of Enclosed Areas
Below the DFE
It is important that the foundation walls contain openings that will permit the automatic entry and exit of
floodwater for buildings that are constructed on extended solid foundation walls or that have other enclosures
below the DFE (see Figure 5E-13).
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5E-12 ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
5E ELEVATION
These openings allow floodwater to reach equal levels on both sides of the walls and thereby lessen the
potential for damage from hydrostatic pressure. While not a requirement for existing buildings built prior
to a community’s joining the NFIP, NFIP regulations require these openings for all new construction and
substantial improvements of existing buildings in SFHAs.
The minimum criteria for design of these openings are:
a minimum of two openings must be provided on different
sides of each enclosed area, having a total net area of not
less than 1 square inch for every square foot of enclosed
area subject to flooding; this is not required if openings are
engineered and certified;
the bottom of all openings shall be no higher than 1 foot
above grade; and
openings may be equipped with screens, louvers, or other
coverings or devices, provided those components permit
the automatic entry and exit of floodwater and do not
reduce the net open area to less than the required open area.
It is important to make sure that none of the flood openings will be obstructed during a flood event. In wet
floodproofed buildings, openings are sometimes obstructed by drywall or other wall coverings (Figure 5E-
14), which can result in significant damage if the opening does not operate as intended. Figure 5E-15 shows
an NFIP-compliant house with attached garage with flood openings to prevent the build-up of hydrostatic
loads on the foundation walls.
CROSS REFERENCE
For additional information on the
regulations and design guidelines
concerning foundation openings,
please refer to FEMA ‘s NFIP
Technical Bulletin 1-08, Openings
in Foundation Walls for Buildings
Located in Special Flood Hazard
Areas in Accordance with
the National Flood Insurance
Program (FEMA, 2008).
Figure 5E-14. A house where flood openings have been covered by insulation and drywall
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5E-13ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
ELEVATION 5E
5E.1.3 Houses on Piers, Columns, or Piles
The process of elevating a house on existing piles, piers, or columns is slightly more complex in that temporary
relocation of the house may be part of the elevation process. With the use of this type of foundation, the house
may need to be lifted off the existing foundation and temporarily relocated on site. The existing foundation is
then removed and/or reconstructed, and the house is reset on the new foundation. In some instances, raising
the home above the working area (instead or relocating off to the side) may provide sufficient room to install
new pier and column foundations and to extend existing piers or columns upward.
5E.1.4 Slab-on-Grade Houses
Although slab-on-grade houses may be the most difficult to raise, a number of elevation options exist with
regard to raising the structure with or without the slab and using a first floor composed of wood or concrete.
If the slab is to be raised with the house, a trench is normally dug under the house to provide a space for
inserting lifting beams. However, intrusive techniques that place beams through the structural walls have
Figure 5E-15.
NFIP-compliant house built
on solid foundation walls
with attached garage
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5E-14 ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
5E ELEVATION
proved to be successful in elevating some slab-on-grade homes, as well. If the existing slab is to remain in
place, the house must be detached from the slab, the structure must be raised separately from the slab, and a
new floor system must be built along with an elevated foundation.
5E.1.4.1 Elevating a Slab-on-Grade Wood-Frame House
The following procedures apply to elevating a wood-frame house with a slab-on-grade foundation:
Elevating without the slab, using a new first floor constructed of wood trusses (see Figures 5E-16
through 5E-20); and
Elevating with the slab intact (see Figures 5E-21 through 5E-23). The basic order of steps required
for raising a slab on grade house with slab intact is illustrated in Figures 5E-21 through 5E-23;
implementation demands highly specialized skill and equipment that are beyond the scope of
this manual.
Figure 5E-16.
Existing wood-frame
house with slab and
stem-wall foundation
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5E-15ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
ELEVATION 5E
Figure 5E-17. Step 1 of elevating an existing wood-frame house without the slab using a new first floor
constructed of wood trusses: Install steel I-beam network and prepare to lift walls
96
5E-16 ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
5E ELEVATION
Figure 5E-19.
Step 3 of elevating
an existing wood-
frame house without
the slab and with
extended stem wall
using a new first floor
constructed of wood
trusses: Set house on
new foundation and
remove I-beams
Figure 5E-18.
Step 2 of elevating
an existing wood-
frame house without
the slab using a new
first floor constructed
of wood trusses:
Lift house, extend
masonry foundation
wall, and install wood
floor trusses; relocate
utility and mechanical
equipment above
flood level
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5E-17ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
ELEVATION 5E
Figure 5E-20.
Cross-section of elevated
wood-frame house (slab
not raised) with extended
stem-wall foundation
and newly installed wood
truss floor
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5E-18 ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
5E ELEVATION
Figure 5E-21. Step 1 of elevating an existing wood-frame house with stem wall foundation and the slab intact:
Excavate under existing slab and install network of steel I-beams. Step 2 (not shown): Raise the wood-frame
house with the slab intact, extend foundation stem walls, and install new piers.
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5E-19ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
ELEVATION 5E
Flood level
Depending on final
height of extended
foundation, area under
home may be used only
for parking, building
access, or storage
ing on final
The finished product
Figure 5E-22.
Step 3 of elevating an
existing wood-frame
house with stem wall
foundation and the slab
intact: Set the house on
the new foundation and
remove the I-beams
5E.1.4.2 Elevating a Slab-on-Grade Masonry House
The following alternatives apply to elevating a masonry house with a slab-on-grade foundation:
elevate a slab-on-grade masonry structure with the slab intact;
elevate a slab-on-grade masonry structure without the slab, and using a first floor constructed of
wood framing;
install an elevated concrete slab within an existing masonry structure;
install an elevated wood-frame floor system within an existing masonry structure;
create a new masonry livable area on top of an existing one-story masonry structure; and
create a new wood-frame livable area on top of an existing one-story masonry structure.
5E.1.5 Heavy Building Materials/Complex Design
The elevation process becomes even more complex with added weight, height, or complex design of the
house. Brick or stucco veneers may require removal prior to elevation. Combination foundations (i.e., slab-
on-grade and basement) should be evaluated jointly, as well as separately, and the worst case scenario utilized
for design purposes. Building additions may need to be elevated independently from the main structure.
Due to the extreme variability of structural conditions, a structural engineer should evaluate the suitability
of lifting this type of home.
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5E-20 ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
5E ELEVATION
Figure 5E-23.
Cross-section of elevated
wood-frame house with
stem wall foundation and
the slab intact
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5E-21ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
ELEVATION 5E
The entire elevation design process is illustrated with a detailed example of the design for a crawlspace house
(Figure 5E-24).
Figure 5E-24.
Design process for
an elevated house on
foundation walls
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5E-22 ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
5E ELEVATION
5E.2 Field Investigation Concerns
To determine whether elevation is an appropriate retrofit technique for a particular building, a field
investigation should be performed. In addition to a site visit and inspection, a data review and code search
should be conducted.
5E.2.1 Property Inspection and Existing Data Review
During the field investigation, the designer should inspect the property and review existing data to confirm
the applicability of the selected alternative and to confirm specific design guidance such as the height of
elevation and type of foundation to be utilized. The designer should utilize the guidance presented in Chapter
5. Much of the data has been previously discussed in Chapters 3 and 4. At a minimum, the designer should
collect information on the checklist in Figure 5E-25.
5E.2.2 Code Search
During the field investigation, the designer should also conduct a search of local floodplain ordinances,
local and State building codes, restrictions to deeds, restrictions in subdivisions, and zoning regulations. In
addition, a visit with the local building official should be planned to determine any special requirements for
the locality. During the code search, the following should be determined:
elevation and foundation requirements per the floodplain ordinance and flood hazard map;
requirements of the building code that governs the elevation project;
design wind speed;
design seismic zone;
ground snow loads;
frost depths;
restrictions on height (overall building, portions of building relative to materials in use, allowable
height/thickness ratios); and
restrictions on foundations.
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5E-23ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
ELEVATION 5E
Figure 5E-25. Elevation Field Investigation Worksheet
Elevation Field Investigation Worksheet
Owner Name:____ ___________________________________Prepared By:______________________________________
Address ______________________________________________________Dat:_____ _______________________
Property Locatio
e:___
______________________________________________________________________________
Does site topography data cover required are
n:_____
Yea? No
Additional data required:
Any construction access issues?
Site and building utilities identifie
s
Yed? No
Potential utility conflicts identified
s
Ye? No
Describe conflicts
s
_____________________________________________________________________________
Review homeowner preferences:
: _____
____________________________________________________________________
Can aesthetics reconcile with site and building constraints
____
Y? No
How
es
Confirm type and condition of existing framing:
member size
?
spas connectionns supports
Confirm type and condition of foundation:
typ
s
depte sizeh
Confirm types and condition of existing construction materials:
ro
flooof wall foundationr s
Confirm soil information:
typ
depth of roe bearing capacick susceptibility to erosion and scour
Confirm characteristics of flood-related hazards:
base flood elevation (BFE
ty
velocit) design flood elevation (DFEy frequency
durati
)
potential for debris flo
Confirm characteristics of non-flood-related hazards:
w
on w
seismiind snoc othw er
w accessibility considerations:
access/egre special resources for elderly, disabled, children
tectural constraints noted
ss
____________________________________________________________________
arance available to install lifting beams and jacking equipment
: _____
Y? No
k local codes/covenants for height or appearance restrictions:
deed/subdivision rul
es
local building ces
ctions:________________________________________________________________________ ___
odes
____________
Revie
Archi
Is cle
Chec
Restri
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5E-24 ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
5E ELEVATION
5E.3 Design
The design process for an elevated structure shown in Figure 5E-24 consists of the following steps:
Step 1: Calculate the vertical loads.
The computation of vertical loads, which includes building
dead and live loads (gravity loads) and buoyancy forces, was
presented in Chapter 4.
Snow Loads: There are no “typical” equations for houses, since
the calculation of snow loads depends on the building code in
use, the geographic area in which the house is located, and the
size and shape of the house and roof. The governing building
code will clearly spell out the correct procedure to follow. Most
procedures are simple and straightforward. Some houses will
be more complex due to their shape or the quantity of snow
that must be allowed for. However, the general procedures are
as follows:
consult snow maps in the building code and/or local
requirements with the local building official to determine
the ground snow load;
determine the importance factors;
analyze the surrounding terrain, trends in snow patterns,
and slope of roof to determine the exposure factors;
determine the snow load;
determine the considerations for drifting snow by
examining any adjacent house or structure, a mountain above the house, or higher roofs; and
determine the considerations for sliding snow by examining the steep slope on the roof or higher roofs.
Step 2: Calculate the lateral loads.
The calculation of building lateral loads includes wind, seismic, and flood-related loads. One objective
of the wind and seismic analysis is to determine which loading condition controls the design of specific
structural components.
Wind Analysis: There are no “typical” equations for houses, since the calculation of wind loads depends
upon the building code in use and the size and shape of the house. The governing building code will clearly
spell out the correct procedure to follow. Most procedures are simple and straightforward. Some houses
will be more complex due to their shape. However, the general procedure, as discussed in Chapter 4, is
presented below.
CROSS REFERENCE
To illustrate the design
process, a worked example
is shown in Appendix C for
Steps 1-7. Information on Step
9 is presented in Chapter 5F.
The designer should refer to
local codes for guidance on
Steps 8 and 10. The example
demonstrates numerous
considerations necessary for
an elevation project, but is not
technically exhaustive.
NOTE
If the governing building code
does not provide applicable
guidance on loading associated
with flooding, wind, seismic, or
snow, refer to ASCE 7.
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5E-25ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
ELEVATION 5E
determine the wind speed and pressure by consulting
wind maps within the building code, and checking local
requirements with the local building official;
determine the importance factors and the exposure
category;
determine the wind gust and exposure factors and analyze
the building height and shape, whether the wind is parallel
or perpendicular to the roof ridge, and whether it is
windward or leeward of roofs/walls;
determine the wind load; and
distribute the load to resisting elements based upon the
stiffness of shear walls, bracing, and frames.
Seismic Analysis: There are no “typical” equations for houses since the calculation of seismic loads depends
upon the building code in use and the size and shape of the house. The governing building code will clearly
spell out the correct procedures to follow. Some houses will be more complex due to their shape. However,
the general procedures, as discussed in Chapter 4, are presented below.
calculate the dead loads by floor, including permanent dead loads (roof, floor, walls, and building
materials) and permanent fixtures (cabinets, mechanical/electrical fixtures, stairs, new locations for
utilities, etc.);
determine if the snow load must be included in the dead load analysis; most building codes require the
snow load to be included for heavy snow regions and will list these requirements;
determine the seismic zone and importance factors;
determine the fundamental period of vibration (height of structure materials used in building);
determine the total seismic lateral force by analyzing site considerations, building weights, and the type
of resisting system;
distribute the loads vertically per the building code, keeping in mind the additional force at the top of
the building; and
distribute the loads horizontally according to the building code and the stiffness of resisting elements.
The code-prescribed minimum torsion of the building (center of mass versus center of rigidity), shear
walls, bracing, and frames must be considered.
Flood-Related Forces: The computation of flood-related forces was presented in Chapter 4 and includes
the following:
determine the DFE;
determine the types of flood forces (hydrostatic or hydrodynamic);
determine the susceptibility to impacts from debris (ice, rocks, trees, etc.);
NOTE
ASCE 7 and the IRC provide
basic wind speed maps showing
wind velocities and frequencies.
If the local code enforced is the
IRC, the designer should refer to
the IRC wind speed map (Figure
4-19). If no local code is in force,
the designer should refer to ASCE
7, Minimum Design Loads for
Buildings and Other Structures.
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5E-26 ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
5E ELEVATION
determine the susceptibility to scour;
determine the applicability of and susceptibility to alluvial fans;
determine the design forces; and
distribute the forces to resisting elements based upon stiffness.
Step 3: Check ability of existing structure to withstand additional loading.
Chapter 4 presented general information on determining the ability of the existing structure to withstand
the additional loadings imposed by retrofitting methods. The process detailed below is similar for each of the
building types most people will encounter. First, the expected loadings are tabulated and compared against
allowable amounts determined from soil conditions, local code standards, or building material standards.
The following list of existing building components and connections should be checked.
Roofs: The plywood roof diaphragm, trusses, connections, and uplift on roof sheathing should be capable
of resisting the increased wind and seismic loads. The Engineered Wood Association (http://www.apawood.
org) has published several references that are useful in this calculation, including APA SR-1013, Design for
Combined Shear and Uplift from Wind (APA,2011) and APA Form T325, Roof Sheathing Fastening Schedules
for Wind Uplift (APA, 2006).
These reference materials or the local building codes will give the designer the necessary plywood thicknesses
and connection specifications to resist the expected loadings and/or will provide loading ratings for specific
material types and sizes.
If the roof diaphragm and sheathing are not sufficient to resist the increased loading, the design can strengthen
these components by:
increasing the thickness of the materials; and/or
strengthening the connections with additional plates and additional fasteners.
Roof Framing-to-Wall Connections: The roof framing connections to walls should be checked to ensure
that they will resist the increased wind loads. Of critical importance are the gable ends, where many wind
failures occur. The Engineered Wood Association has published several references that are useful in this
calculation, including APA SR-1013, Design for Combined Shear and Uplift from Wind (APA, 2011) and APA
Form L350, Diaphragms and Shear Walls (APA, 2007).
These reference materials or the local building codes will
give the designer the necessary truss size, configuration, and
connection specifications to resist the expected loadings, and/
or will provide loading ratings for specific truss and connection
types and sizes.
If the roof trusses and wall connections are not sufficient to
resist the increased loading, the design can strengthen these
components by:
CROSS REFERENCE
For additional information on the
performance of various building
system products, refer to product
evaluation reports prepared
by the model code groups or
the National Evaluation Service
(NES).
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5E-27ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
ELEVATION 5E
increasing the amount of bracing between the trusses; and/or
strengthening the connections with additional plates and additional fasteners.
Upper Level Walls: The upper level walls are subject to increased wind pressure and increased shear due to
increased roof loads. Both the short and long walls should be checked against the shear, torsion, tension, and
deflection, utilizing the governing loading condition (wind or seismic).
The Engineered Wood Association has published several references that are useful in this calculation,
including APA SR-1013, Design for Combined Shear and Uplift from Wind (APA, 2011) and APA Form L350,
Diaphragms and Shear Walls (APA, 2007).
These reference materials or the local building codes will give the designer the necessary wall size and
configuration and connection specifications to resist the expected loadings and/or will provide loading
ratings for specific wall types, sizes, and connection schemes.
If the upper level walls are determined to be unable to withstand the increased loadings, the designer is
faced with the difficult task of strengthening what amounts to the entire house. In some situations, this may
be cost- prohibitive, and the homeowner should look for another retrofitting method, such as relocation.
Measures the designer could utilize to strengthen the upper level walls include:
adding steel strapping (cross bracing) to interior or exterior wall faces;
adding a new wall adjacent to the exterior or interior of the existing wall;
bolstering the interior walls in a similar fashion; and/or
increasing the number and sizes of connections.
Floor Diaphragm: The floor diaphragm and connections are subject to increased loading due to wind,
seismic forces, and flood. The existing floor diaphragm and connections should be checked to ensure that
they can withstand the increased forces that might result from the elevation.
The Engineered Wood Association has published several references that are useful in this calculation,
including APA Form Y250. Shear Transfer at Engineered Wood Floors (APA, 1999) and APA Form L350,
Diaphragms and Shear Walls (APA, 2007).
These reference materials or the local building codes will give the designer the necessary floor size and
configuration and connection specifications to resist the expected loadings, and/or will provide loading
ratings for specific floor types, sizes, and connection schemes.
If the floor diaphragm or connections are determined to be unable to withstand the increased loadings, the
designer could strengthen these components by:
adding a new plywood layer on the bottom of the existing floor diaphragm;
increasing the number and size of bracing within the floor diaphragm; and
increasing the number and size of connections.
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5E-28 ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
5E ELEVATION
Step 4: Analyze the existing foundation.
The existing foundation should be checked to determine its ability to withstand the increased gravity loads
from the elevation, the increased lateral loads due to soil pressures from potential backfilling, and the increased
overturning pressures due to seismic and wind loadings. The designer should tabulate all of the gravity loads
(dead and live loads) plus the weight of the new foundation walls to determine a bearing pressure, which is
then compared with the allowable bearing pressure of the soil at the site. Not including expected buoyancy
forces in this computation will yield a conservative answer.
If the existing footing is insufficient to withstand the additional loadings created by the elevated structure,
the design of foundation supplementation should be undertaken. The foundation supplementation may be
as straightforward as increasing the size of the footing and/or more substantial reinforcement. The designer
may refer to the ACI manual for footing design, recent texts for walls and footing design, and applicable
codes and standards.
Step 5: Design the new foundation walls.
The design of a new foundation, whether solid or open, is
usually governed by the local building codes. These codes will
have minimum requirements for foundation wall sizes and
reinforcing schemes, including seismic zone considerations.
The designer should consult the appropriate code document
tables for minimum requirements for vertical wall or open
foundation reinforcement.
For new slab applications where the lower level is allowed to flood and the slab is not subject to buoyancy
pressures, the designer can use the Portland Cement Association document Concrete Floors on Ground (2008)
as a source of information to select appropriate thicknesses and reinforcing schemes based upon expected
loadings. The slab loadings will vary based upon the overall foundation design and the use of the lower floor.
Step 6: Design top of foundation wall connections.
Top of wall connections are critical to avoid pullout of the sole plate, floor diaphragm, and/or sill plate
from the masonry foundation. A preliminary size and spacing of anchor bolts is assumed, and uplift, shear,
and tension forces are computed and compared against the allowable loads for the selected bolts. Where
necessary, adjustments are made to the size and spacing of the anchor bolts to keep the calculated forces below
the allowable forces. Connections should be designed for all appropriate load combinations as discussed
in Chapter 5.
Step 7: Design the sill plate connections.
The existing sill plate connections will be subject to increased lateral loads and increased uplift forces due to
increased wind and buoyancy loading conditions. The sill plate is designed to span between the anchor bolts
and resist bending and horizontal shear forces. The designer should refer to the appropriate wood design
manual that provides recommended compression, bending, shear, and elasticity values for various sill plate
materials. Using these values, the designer checks the connection against the expected forces to ensure that
the actual forces are less than the allowable stresses. If the sill plate connection is insufficient to withstand
expected loadings, the size of the sill plate can be increased (or doubled), and/or the spacing of the anchor
bolts can be reduced.
CROSS REFERENCE
For wet floodproofing
applications, where openings in
foundation walls are necessary,
refer to Chapter 5W, Wet
Floodproofing.
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5E-29ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
ELEVATION 5E
Step 8: Design new access.
The selection and design of new access to an elevated structure is done in accordance with local regulations
governing these features. Special homeowner requirements, such as for aesthetics, handicapped accessibility,
and/or special requirements for children and the elderly, can be incorporated using references previously
discussed in Chapter 3.
Incorporating the new access often applies to multiple egress locations and may present a unique challenge
to the designer as greater area is required on the existing site to accommodate the increase in elevation from
adjacent grade to egress. A particular obstacle may arise with attached garages where the living space is elevated
and the garage slab remains at original grade as allowed for areas designated for building access, parking, and
storage only. Besides the area and height constraints required for the additional stairs to the elevated egress,
the designer must also resolve drainage and aesthetic issues created by the newly discontinuous roof system.
Connection of the new access to the house should be designed in accordance with the local codes. The
foundation for the access measure will either be freestanding and subject to its own lateral stability requirements
or it will be an integral part of the new elevated structure. In either case, analysis of the structure to ensure
adequate foundation strength and lateral stability should be completed in accordance with local codes.
It should be noted that any access below the BFE should incorporate the use of flood-resistant materials.
The designer should refer to FEMA’s NFIP Technical Bulletin 2-08, Flood Damage-Resistant Materials
Requirements for Buildings Located in Special Flood Hazard Areas in Accordance with the National Flood
Insurance Program (FEMA, 2008).
Step 9: Design the utilities extensions.
The field investigation will reveal the specific utility systems that will require relocation, extension, or
modification. Whenever possible, utility systems should be relocated above the DFE. Local utility companies
should be contacted about their specific requirements governing the extension of their utility service. In
many instances, the local utility company will construct the extension for the homeowner. Critical issues in
this extension process include:
handling of utilities encased in the existing slab or walls;
coordination of disconnection and reconnection;
any local codes that require upgrades to the utility systems as part of new construction or substantial
repair or improvement;
introduction of flexible connections on gas, water, sewer, and oil lines to minimize potential for
seismic damage;
potential for relocation or elevation of electrical system
components from existing crawlspace and/or basement
areas; and
design of separate GFI-type electrical circuits and use of
flood-resistant materials in areas below the BFE.
CROSS REFERENCE
Guidance on the selection of an
elevation or relocation contractor
is provided in Chapter 5R,
Relocation.
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5E-30 ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
5E ELEVATION
Step 10: Specify the increased insulation requirements.
Elevated floors and extended utility system components may increase the potential for heat loss through
increased exposure and airflow and necessitate additional insulation. The designer should evaluate the energy
efficiency of each aspect of the project, compare existing insulation (R-values) against the local building
code, and specify additional insulation (greater R-value) where required.
5E.4 Construction Considerations
Following are some important points for consideration both prior to and during implementation of a structure
elevation project.
Prior to elevating any house:
obtain all permits and approvals required;
ensure that all utility hookups are disconnected (plumbing, phone, electrical, cable, and mechanical);
estimate the lifting load of the house; and
identify the best location for the principal lift beams, lateral support beams, and framing lumber, and
evaluate their adequacy (generally performed by a structural engineer or the elevation contractor).
5E.4.1 Slab-on-Grade House, Not Raising Slab with House
Procedures for elevating a slab-on-grade house without raising the slab:
holes are cut for lift beams in the exterior and interior walls;
main lifting beams are inserted;
holes are cut for the lateral beams;
lateral beams are inserted;
bracing is installed to transfer the loads across the support walls and lift remaining walls;
jacks are moved into place and structure is prepared for lifting;
straps and anchors used to attach house to slab-on-grade are released;
the house is elevated and cribbing installed;
slab around edges is removed to allow for new foundation;
the new foundation is constructed;
new support headers and floor system are installed;
any required wind and seismic retrofit is completed;
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5E-31ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
ELEVATION 5E
house is attached to new foundation;
all temporary framing is removed, holes are patched;
all utilities are reconnected;
new stairways and access are constructed; and
all utilities below the DFE are floodproofed.
5E.4.2 Slab-on-Grade House, Raising Slab
Procedures for elevating a slab-on-grade house and raising the slab:
trenches are excavated for placement of all support beams beneath slab;
lifting and lateral beams are installed;
jacks are moved into place and the structure is prepared for lifting;
the house is elevated and cribbing installed;
the new foundation is constructed;
any required wind and seismic retrofit is completed;
house is attached to new foundation;
support beams are removed;
access holes are patched;
all utilities are reconnected;
new stairways and access are constructed; and
all utilities below the DFE are floodproofed.
5E.4.3 House Over Crawlspace/Basement
Procedures for elevating a house over a crawlspace or basement:
masonry is removed as necessary to allow for placement of support beams;
main lifting beams are installed;
lateral beams are installed;
jacks are moved into place and the structure is prepared for lifting;
all connections to foundation are removed;
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5E-32 ENGINEERING PRINCIPLES AND PRACTICES for Retrofitting Flood-Prone Residential Structures
5E ELEVATION
house is elevated and cribbing installed;
existing foundation walls are raised or demolished, depending on whether the existing foundation walls
can handle the new loads;
new footings and foundation walls are constructed if the existing foundation walls/footings cannot
withstand the additional loading;
basement is backfilled where appropriate;
house is attached to new foundation;
support beams are removed;
access holes are patched;
all utilities are reconnected;
new stairways and access are constructed; and
all utilities below the DFE are floodproofed.
5E.4.4 House on Piers, Columns, or Piles
If the house is to remain in the same location, the house will most likely need to be temporarily relocated
to allow for the footing and foundation installation. If the house is being relocated within the same site,
the footings should be constructed prior to moving the house. Procedures for elevating a house on piers,
columns, or piles:
main support beams are installed;
lateral beams are installed;
jacks are moved into place and the structure prepared for lifting;
house is elevated and cribbing is installed;
if the house is being relocated, see section 5R;
existing foundation is demolished and removed and new pier and column foundation is installed or
existing foundation elements are extended upward and reinforced as needed
house is attached to new foundation;
support beams are removed;
all utilities are reconnected;
new stairways and access are constructed; and
all utilities below the DFE are floodproofed.
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Sec. 38.35.060.-Zoning variances.
A. Application. A request for one or more variance shall be made by filing an application, with
appropriate fees, with the planning department at least 30 calendar days prior to the review
authority's consideration ofthe application and shall be accompanied by the materials described in
section 38.41. 160.
B. Investigation of facts. The review authority shall cause to be made such investigation offacts bearing
on the application as will provide necessary information to ensure that the action on each such
application is consistent with the intent and purpose of this chapter.
C. Criteria for consideration and decision. In acting on an application for a variance, the review authority
shall designate such lawful conditions as will secure substantial protection for the public health, safety
and general welfare, and shall issue written decisions setting forth factual evidence that the variance
meets the standards of MCA 76-2-323 in that the variance:
1. Will not be contrary to and will serve the public interest;
2. Is necessary, owing to conditions unique to the property, to avoid an unnecessary hardship which
would unavoidably result from the enforcement of the literal meaning of this chapter:
a. Hardship does not include difficulties arising from actions, or otherwise be self-imposed, by
the applicant or previous predecessors in interest, or potential for greater financial returns;
and
b. Conditions unique to the property may include, but are not limited to, slope, presence of
watercourses, after the fact imposition of additional regulations on previously lawful lots, and
governmental actions outside of the owners control;
3. Will observe the spirit of this chapter, including the adopted growth policy, and do substantial
justice;
4. In addition to the criteria specified above, in the case of a variance relating to the flood hazard
provisions of article 31 of this chapter:
a. Variances shall not be issued for areas within a floodway if any additional increase in flood
elevations or velocities after allowable encroachments into the floodway fringe would result;
b. Variances shall only be issued upon:
(1) A determination that the granting of a variance will not result in increased flood hazards,
present additional threats to public safety, be an extraordinary public expense, create
nuisances, cause fraud, victimize the public, or conflict with existing state and local laws;
(2) A determination that the proposed use would be adequately flood proofed as specified
in article 31 of this chapter;
(3) A determination that a reasonable alternate location outside the floodplain is not
available;
(4) A determination that the variance requested is the minimum necessary to afford relief,
considering the flood hazard; and
(5) Approval of the state department of natural resources and conservation, upon request
from the city, prior to formally approving any permit application that is in variance to
these regulations.
D. Authorization and limitations on approval.
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312512016 Bozeman, MT Code c:l Ordinances
1. The review authority may, after public notice, opportunity for public comment, and consideration
of the application, deny, approve or conditionally approve all requests for variances meeting all
the criteria ofthis section, including:
a. Requests to modify dimensional or other numerical requirements of this chapter;
b. Requests for multiple variances;
c. Requests to modify flood hazard district requirements subject to the provisions of article 31
of this chapter, except that no variance shall be granted to allow construction of buildings
within the floodway of a 1 00-year frequency flood as defined in title 76, chapter 5, Montana
Code Annotated (MCA 76-5-101 et seq.); and
d. Requests for variances in conjunction with conditional use permits. Approvals of all such
variances shall be conditioned upon review authority approval of the conditional use permit.
2. The scope and extent of the variance shall be limited to the minimum relief necessary to provide
reasonable use of the property.
3. In no case may the review authority grant variances to allow uses not already permitted pursuant
to this chapter or alter administrative requirements of this chapter. Permission to change uses
allowed on a parcel may be sought through a zone map amendment, or an amendment to the
text of the applicable zoning district, or through a planned unit development subject to article
38.20.
4. Notifications of approval for variances related to flood hazard requirements of article 31 of this
chapter shall notify the applicant that:
a. The issuance of a variance to construct a building below the 1 00-year floodplain elevation will
result in increased premium rates; and
b. Such construction below the 1 00-year flood elevation increases risks to life and property.
E. Effective time for decisions; variances void when. The decision of the review authority shall be final
except as provided in section 38.35.080. If a building permit or land use permit is not obtained for the
subject property within six months from the date of the review authority's decision, the variance shall
be automatically canceled and become null and void.
F. Variances. Variances are subject to MCA 76-2-321 through 76-2-328.
(Ord. No. 1645, § 18.66.060, 8-15-2005; Ord. No. 1670, § 18.66.060, 8-28-2006; Ord. No. 1693, §
24(18.66.060), 2-20-2007; Ord. No. 1769, exh. L(18.66.060), 12-28-2009; Ord. No. 1827, § 8, 9-1 0-2012)
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Model Regulations Feb 20 2014.doc
49 February 20, 2014
SECTION 12. VARIANCES
12.1 GENERAL - A variance from the minimum development standards of these
regulations may be allowed. An approved variance would permit construction in a
manner otherwise as required or prohibited by these regulations. ((44 CFR 59.1) (ARM 36.15.218))
12.2 VARIANCE APPLICATION REQUIREMENTS:
1. Prior to any consideration of a variance from any development standard in these regulations, a completed Floodplain Permit application and required supporting
material must be submitted.
2. Additionally, supporting materials in a Variance application specific to the
variance request including facts and information addressing the criteria in this Section must be submitted.
3. If the Floodplain permit application and Variance application is deemed not
correct and complete, the Floodplain Administrator shall notify the applicant of
deficiencies within a reasonable time not to exceed 30 days. Under no circumstances should it be assumed that the variance is automatically granted.
12.3 NOTICE REQUIREMENTS FOR FLOODPLAIN VARIANCE APPLICATION
Public Notice of the Floodplain permit application and Variance application shall be
given pursuant to Section 8.2.
12.4 EVALUATION OF VARIANCE APPLICATION
1. A Floodplain permit and Variance shall only be issued upon a determination that
the variance is the minimum allowance necessary, considering the flood hazard, to afford relief from these regulations and provided all of the following criteria are met:
1. There is a good and sufficient cause. Financial hardship is not a good and
sufficient cause; (44 CFR 60.6(a)(3)) 2. Failure to grant the variance would result in exceptional hardship to the
applicant; (44 CFR 60.3(a)(3)) & ARM 36.15.218(b))
3. Residential and nonresidential buildings are not in the Floodway except for alterations or substantial improvement to existing buildings, Residential dwellings including basements and attached garages do not have the
lowest floor elevation below the Base Flood Elevation;
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Model Regulations Feb 20 2014.doc
50 February 20, 2014
4. Any enclosure including a crawl space must meet the requirements of Section 10.2.14, Wet Flood Proofing if the enclosure interior grade is at or
below the Base Flood Elevation;
5. Granting of a variance will not result in increased flood heights to existing buildings, additional threats to public safety, extraordinary public expense, create nuisances, cause fraud on or victimization of the public, or conflict
with other existing local laws or ordinances; (44 CFR 60.6 (a)(3) & (ARM
36.15.218(a))
6. The proposed use is adequately flood proofed; (ARM 36.15.218(c))
7. The variance is the minimum necessary, considering the flood hazard, to
afford relief; (44 CFR 60.6(a)(4))
8. Reasonable alternative locations are not available; (MCA 76-5-406(3) & ARM 36.15.218(d))
9. An encroachment does not cause an increase to the Base Flood Elevation
that is beyond that allowed in these regulations; and (44 CFR 60.6(a)(1))
10. All other criteria for a Floodplain permit besides the specific development
standard requested by variance are met.
2. An exception to the variance criteria may be allowed as follows:
1. For either new construction of a structure outside of the Floodway only or
for substantial improvements or an alteration of a structure, on a lot of
one-half acres or less that is contiguous to and surrounded by lots with
existing structures constructed below the Base Flood Elevation; or (44
CFR 60.6(a).
2. For Historic Structures – variances may be issued for the repair or
rehabilitation of historic structures upon a determination that the proposed
repair or rehabilitation will not preclude the structure's continued
designation as a historic structure and the variance is the minimum relief necessary to preserve the historic character and design of the structure.
The historic nature of the building must be designated as a preliminary or
historic structure by U.S. Secretary of Interior or an approved state or local
government historic preservation program. (44 CFR 60.6(a))
12.5 DECISION
1. The {Board of Adjustment, County Commission, or other panel} shall:
1. Evaluate the Floodplain permit application and Variance application using
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51 February 20, 2014
the criteria in Section 12.4, and the application requirements and minimum development standards in Section 9 and 10;
2. Make findings, and approve, conditionally approve or deny a Floodplain
permit and variance within 60 days of a complete application. 3. If approved, attach conditions to the approval of Floodplain permit and
Variance including a project completion date and inspections during and
after construction.
4. Notify the applicant that the issuance of a Floodplain permit and Variance
to construct a structure not meeting the minimum building requirements in
these regulations may result in increased premium rates for flood
insurance and that flood insurance premiums are determined by actuarial
risk and will not be modified by the granting of a variance. (44CFR 60.6(a))
5. Submit to the Floodplain Administrator a record of all actions involving a
Floodplain permit and variance, including the findings and decision and send a copy of each variance granted to DNRC.(44 CFR 60.6(a)(6) & MCA 76-5-405)
12.6 JUDICIAL REVIEW Any person or persons aggrieved by the Floodplain permit and variance decision may
appeal such decision in a court of competent jurisdiction.
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City of Bozeman
FLOOD INSURANCE RATE MAP UPDATES
Promoting flood-risk awareness
www.floodplain.mt.gov
MANAGEMENT
FLOODPLAIN
FEMA 90-Day Appeal & Comment Period
THE FEMA APPEAL & COMMENT PROCESS
PROJECT TIMELINE (tentative)
Winter 2016
Draft floodplain
maps produced
Fall 2016
Preliminary Flood
Insurance Rate Maps
produced
Winter 2017
FEMA Appeal
and Comment
Period begins
Spring 2017
FEMA Appeal
and Comment
Period ends
Summer 2017
Appeals and
Comments resolved
Spring 2018
New Flood Insurance
Rate Maps become
effective
Fall 2017
New Flood Insurance
Rate Maps finalized
90 days
FEMA requires a 90-day public Appeal & Comment Period for proposed Flood Insurance Rate Map changes.
Public review of proposed Flood Insurance Rate Map changes is an important part of the map update process
because it ensures that map data is as accurate as possible. The Appeal & Comment Period for this project is
projected to begin Winter 2017.
APPEALS
An Appeal is a technical issue with a Preliminary Flood Insurance
Rate Map. Some common types of Appeals include a flood elevation
objection or a delineation of floodplain boundary dispute.
Appeals often require supporting documentation such as an Elevation
Certificate, topographic map, engineering study, photographs, etc.
Visit www.fema.gov and search “Criteria for Appeals of Flood
Insurance Rate Maps” for more information about Appeals.
COMMENTS
A Comment is map error found on a Preliminary Flood Insurance
Rate Map. Some common types of Comments include the
correction of a street name, city limit boundary, etc. Comments
do not generally require supporting documentation.
The 90-Day Appeal & Comment
Period is projected to begin Winter
2017. You may only submit an
Appeal or Comment during the
official Appeal & Comment Period.
If you have an Appeal or Comment,
the City encourages you to begin
organizing materials early so that
you are prepared for the 90-Day
Appeal & Comment Period.
Please contact us directly for more information.
Brian Heaston
Bozeman City Engineering
bheaston@bozeman.net
406.582.2280
Tiffany Lyden
MT DNRC
tlyden@mt.gov
406.444.0599 119