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HomeMy WebLinkAbout19--411 N. Tracy Structural Assessment Final STAMPED LOCAL EXPERTISE, NATIONAL EXPERIENCE. LEARN MORE AT DCI-ENGINEERS.COM July 11, 2024 Attn: Catherine Woods 411 North Tracy Avenue Bozeman, MT 59718 Re: 411 North Tracy Avenue – Structural Conditions Assessment Bozeman, MT Dear Catherine: At your request, DCI Engineers performed a preliminary structural conditions assessment of the existing residence at 411 North Tracy Ave. in Bozeman, MT. On July 2, 2024, Lindsey Bosworth, PE and Andrew Raney, EIT visited the residence to assess the buildings’ condition and document the visible primary structural elements and deficiencies. The intent of the visit was to evaluate the structural capacity and compliance of the existing members as well as address the potential of the structure to accommodate a major remodel. The findings and recommendations in this report are based on visual observations made on site during the site visit. Our assessment is based on the 2021 International Existing Building Code (IEBC) and the 2021 International Building Code (IBC). If you have any immediate questions regarding the enclosed report, or if we can be of further assistance, please contact Lindsey Bosworth at (406) 602-4023 or at lbosworth@dci-engineers.com Sincerely, DCI Engineers Lindsey Bosworth, PE Senior Project Manager Andrew Raney, EIT Project Engineer Enclosure: 411 North Tracy Ave. – Structural Conditions Assessment LOCAL EXPERTISE, NATIONAL EXPERIENCE. LEARN MORE AT DCI-ENGINEERS.COM 411 North Tracy Avenue – Structural Conditions Assessment The residence is located at 411 North Tracy Avenue in Bozeman, Montana, It is a two-story wood-framed residential structure. The building is divided into two units: one encompassing the main floor of the residence and the other the second floor. The foundation of the building is primarily stacked stone/rubble with a small concrete basement in the rear. This report addresses the condition of structural elements based on visual observation. The intent of this report is to identify the primary structural systems of the building and identify and interpret the structural implications of future use, upgrades, repairs, and proposed modifications. This report is general in nature and qualitative in approach. A more in-depth structural analysis and design effort would be required for any remodel or upgrade efforts. Document & Code Review No original construction documents were available for this building. This assessment is based on the requirements of the 2021 International Building Code (IBC) and 2021 International Existing Building Code (IEBC). Existing buildings that may not comply with current building code standards for new construction are governed by the requirements of the IEBC for repairs and alteration work. The IEBC requirements maintain basic life safety, ensure new structural elements are designed to current code and maintain or improve the existing building’s current level of compliance. The IEBC is the adopted code for existing buildings located in the City of Bozeman and governs repairs, alterations, and changes of occupancy to existing structures. Per the IEBC, no lateral or gravity upgrades to the structure are required if the structural elements of the building are not altered or removed. The IEBC also allows for minor changes and alterations to the structure without upgrading the full gravity or lateral systems to current IBC-level standards. Required repairs to the structure can be made in-kind, unless the damage was caused by snow or, in some cases, wind or earthquake loads. Mandatory structural upgrades are triggered by alterations to the existing structure or select required repairs. These triggers can include a change of occupancy, a reroofing project, modifications to more than 30% of the structure, reduction in capacity or increase in demand for specific members, or significant changes in load paths. LOCAL EXPERTISE, NATIONAL EXPERIENCE. LEARN MORE AT DCI-ENGINEERS.COM Structural Observations Lindsey Bosworth, PE and Andrew Raney, EIT of DCI Engineers visited the site on July 2, 2024. Observations occurred at the exterior of the structure, at all interior rooms, and in the attic and crawlspace where possible. Wall, floor, and ceiling finishes were all intact, so observations were limited to those structural elements visible without destructive investigation. Figures referenced below are located at the end of this report. Exterior Walls The exterior walls of the structure were covered by finishes on both sides and could not be observed during the investigation. At the entrance door to the upper unit, horizontal tongue and groove wall plank sheathing was exposed beneath the exterior siding and beyond the framed extents of the door (Figure 1). This is assumed to be typical throughout the exterior of the building. Roof Observation of the roof framing was limited to a small access opening in the entry room of the upper unit. In that location the roof is framed with full sawn 2x4 rafters spaced at 24 inches on center and sheathed with horizontal plank sheathing (Figure 2). No ridge beam or ridge board is present. This construction is typical throughout older Bozeman area homes and relies on ceiling level rafter ties to resist outward thrust of the rafters. Similar roof construction is assumed to exist in the remainder of the roof areas. Second Level Floor Framing Due to floor and ceiling finishes, the second level floor framing was also not observed during the inspection. We have assumed that the floor framing consists of joist members supported by bearing walls. Second level floor framing is noticeably deflected above the first floor kitchen (Figure 3). The ceiling in the kitchen has been previously repaired as evidenced by the white colored spackling present. The ceiling in the northeast main floor bathroom is cracked, spotted and peeling and nearby electrical conduit is discolored (Figure 4). This indicates a previous water intrusion in this location that may have also affected the second floor framing above. Main Level Floor Framing The main level floor framing was observed in two areas: the basement area on the west side of the house, and through a small access door to the crawlspace in the northeast corner of the house. The main level floor framing typically consists of full sawn 2x6 joists spaced at 24 inches on center. Joists span the north-south direction from the exterior foundation walls to intermediate beams located near the center of the structure (Figure 5). In the basement area beams are supported by posts which are then supported by stacked stone/rubble foundation elements. In the typical crawlspace condition the beams are supported directly by stacked stone elements or soil (Figure 6). There was evidence of moisture damage to some floor joists. LOCAL EXPERTISE, NATIONAL EXPERIENCE. LEARN MORE AT DCI-ENGINEERS.COM Foundation The primary perimeter foundation is stacked stone with an applied concrete or parge coat layer at the exterior. There is a basement area at the west end of the building with concrete walls and dirt floors. This area appears to have been added after the initial construction. The clearance below the floor framing varies, with the basement area having approximately 6 feet of clearance and the crawlspace having no more than 2 feet. Previous excavation in the basement area has left some bearing elements undermined (Figure 7) The access to the basement area is a wood framed, cellar-style entry. Both side walls of the entrance are constructed of wood and are retaining soil. The south wall of the entryway is deflected inward and retained soil is visible beyond (Figure 8). Exterior Elements (Porches, stairs) The porch and elevated deck framing at the south side of the house is supported by posts spanning from grade to the second-floor level, and separate, offset posts spanning from the second-floor level to the roof level (Figure 11). The deck boards are showing severe deterioration and the upper deck slopes significantly away from the house. We were unable to determine if there were any existing foundation elements for the deck framing. An exterior enclosed staircase can also be seen in Figure 11 that was likely added after original construction of the building. Structural Analysis This analysis was based on the life-safety requirements of the 2021 IEBC and 2021 IBC. For the purposes of the following discussion, please see the following definitions:  Gravity framing is the structural system used to support the self-weight of the building, the weight of the occupants, and the snow loads on the roof.  Lateral framing is the structural system used to create rigidity and stability for the structure in the event of a design-level earthquake (seismic load) or high-wind event. The structure at 411 North Tracy Avenue is in Seismic Design Category D, which is an area of high seismicity. In addition, the City of Bozeman requires a design roof snow load of 41 pounds-per-square-foot (psf) be used in all new building designs. Based on the occupancy of a structure, live loads are used to represent common loading caused by the weight of the occupants. The current live load for this building is 40 psf for residential use. If the structure would be designed for upgrades, these design values would be considered in design. Gravity Framing We were able to view only a limited portion of the roof framing while on site but can assume that the remainder of the roof is framed in a similar manner. While the roof has supported gravity and snow loads to date and per the IEBC can remain unmodified, this roof would not meet today’s code requirements for gravity or lateral demands. As all walls were covered in finishes during our visit we were unable to observe the wall framing. We assume that the walls are constructed with either 2x4 or 2x6 wall studs, at 16 LOCAL EXPERTISE, NATIONAL EXPERIENCE. LEARN MORE AT DCI-ENGINEERS.COM inches to 24 inches on center. With the dimensions of the building any of these wall framing construction combinations is likely adequate to support floor and roof loads. It is visually apparent that the second-floor joists have previously deflected a significant amount in multiple locations. This deflection could be due to under-designed members or members that were damaged over time. These deformations lead to concerns for the integrity of the existing second floor framing, but causes cannot be verified without demolition of the ceiling finishes and exploration of the existing floor framing. Our access to the main level floor members was also limited but there are noticeable deflections in the first level floors. These deformations, in combination with the noted moisture damage indicate potential structural damage to the floor joists. Foundation The stacked stone foundation likely does not extend below frost depth but is in surprisingly good condition at the perimeter of the building. The applied concrete/parge coat finish does not show signs of cracking or settlement and there were no cracks on the interior finishes to indicate differential settlement of the exterior walls. The rear of the house, where the basement was added, was the exception. In this location signs of ongoing floor settlement were observed in the form of recent wall and trim cracks and inoperable interior doors. This is likely due to continued settlement issues from inadequate bearing and/or moisture affecting the exposed soil and framing members. Lateral Framing Houses constructed during the early 1900’s did not have intentional lateral systems. Nonetheless, the exterior wall sheathing and interior/exterior wall finishes have provided rigidity to the building as a whole for the past century. Horizontal wall plank sheathing, as seen on this structure, is currently accepted as a wood shear wall material but has a much lower capacity than traditional 1/2” plywood or OSB wall sheathing. Although a full lateral analysis is not part of this report, based on experiences with similar houses in the area, the horizontal wall planking is likely adequate at the second floor yet inadequate as a shear wall element in some areas at the lower level. The horizontal floor planking (vs. plywood or OSB sheathing) also has a lower lateral diaphragm capacity. Discussion and Recommendations If the occupancy of a building is not changed and no extensive remodels are performed, existing, even structurally deficient houses, can continue to exist through provisions in the IEBC. The IEBC also allows for repairs to be made to failing or deficient members without upgrades to the building as a whole. However, there are repairs and upgrades that we recommend in this report as an improvement to both life safety and serviceability. Our understanding of the future use of this building is that major renovations and remodel efforts would be included. Per the IEBC, if more than 30% of the structural members are altered as part of a remodel effort, a full current IBC gravity and lateral analysis needs to be performed. In this case that 30% could include changing the roof framing, modifying the existing openings on the exterior walls or modifying the interior bearing wall lines. LOCAL EXPERTISE, NATIONAL EXPERIENCE. LEARN MORE AT DCI-ENGINEERS.COM The recommendations below are based on the assumptions of a full gravity and lateral analysis needing to be performed on the building. Roof Framing Under current code analysis, we anticipate that all or most of the roof framing would prove inadequate for long term continued use of the space. Upgrades could include full replacement with new prefabricated lumber trusses, or attachment of deeper “sistered” members to the existing rafters. Floor Framing The second-floor framing is currently failing serviceability requirements as shown by the heavily deflected joists in the main-level kitchen area. To level the floors, finishes would need to be entirely removed so that additional members or replacement joists could be installed. If floor framing upgrades are performed, it makes sense to also upgrade their supporting interior foundation elements to prevent a recurrence of the existing issues. Due to the extremely shallow crawlspace access, these upgrades cannot be accomplished from the basement and would require removal of areas of the first-floor framing to create new foundation elements. Foundation While settlement issues were seen throughout the structure, they are primarily located at interior bearing elements. Most appear to have occurred in the past and not be ongoing, with the exception of the basement area at the rear of the strucutre. The existing exterior foundation elements are acceptable to continue supporting the load of the structure as it was built and used presently. As mentioned above, it is recommended that the interior foundation elements be upgraded or replaced so appropriate bearing is achieved at all interior bearing locations. Should any additional load be added to the structure, or any significant modifications occur, significant foundation upgrades should be anticipated. Exterior Elements The deck and porch are noticeably and visually deflected and deterioirated. Due to the relatively independent nature of the deck and likely deficient framing or foundation members, we recommend the entire deck and porch be rebuilt. Individual elements can be inspected during demolition and construction for any potential re-use in the new framing. Lateral Elements Bringing this building to current IBC lateral code standards would require removal of exterior finishes, and likely interior finishes at the lower level, and the addition of new wall sheathing and/or additional wall nailing. New roof and floor sheathing would likely be necessary to create roof and floor diaphragms with adequate capacity. Hardware and connections would need to be added throughout to create a continuous lateral load path. This would include clips, nailing, and blocking to connect the roof and floor levels to the shear walls below. At the foundation level, a sill plate and anchorage to the foundation would need to be added as well as hold-downs at locations where uplift forces exceed the LOCAL EXPERTISE, NATIONAL EXPERIENCE. LEARN MORE AT DCI-ENGINEERS.COM resisting dead load of the walls. Post installed anchorage and holdowns will be challenging to install in the rubble foundation and will likely require further foundation upgrades. Summary At a high level, the existing structure can continue in its existing layout and use per the IEBC. Select repairs should be implemented to improve the performance and safety of the building. Improving the serviceability of the building will require interior foundation upgrades that will likely be impossible to install without removing much of the first-floor framing. Re-leveling existing wall and floor deformations will likely require replacement of most or all of the interior finishes. Major modifications or additions to the building will require bringing the structure to current gravity and lateral code requirements. To continue the existing use and the existing floor layout, we recommend repairs to the following items to improve safety for the building inhabitants:  Remove and replace deficient structural elements in the basement area o Replace the two posts and segments of floor beam attached to them o Remove the stacked stone foundation elements and replace with independent concrete spread footings  Further investigate sources of moisture in the crawlspace and basement and actively mitigate  Remove and replace the damaged basement entry framing with new reinforced concrete foundation and walls  Remove and replace the deck/porch structure with adequate framing members and independent foundation elements. Verify that the handrail is intact and meets code requirements. To improve serviceability of the existing building as-is:  Remove floor/ceiling finishes and upgrade or replace the floor joists  Lift bearing elements (interior walls and posts) to create a more plumb structure. This will likely require replacing most or all rigid finishes.  Replace existing deficient interior footings elements with reinforced concrete spread footings. If the structure is to be involved in a renovation that would require a full lateral and gravity structural analysis, the following would be required:  New roof sheathing added above the existing roof planks  Upgrades to the roof framing members  Removal of interior finishes to expose second floor framing, wall framing, and main- floor framing. Further analysis and upgrades would likely be required for the floor framing members at both levels.  Replacement of existing exterior foundation elements where new loading is introduced. This could be achieved through 1) underpinning for sequential LOCAL EXPERTISE, NATIONAL EXPERIENCE. LEARN MORE AT DCI-ENGINEERS.COM foundation replacement with concrete walls and footings or 2) a temporary building move for comprehensive foundation replacement  Replacement of the basement entry framing LOCAL EXPERTISE, NATIONAL EXPERIENCE. LEARN MORE AT DCI-ENGINEERS.COM Appendix 1: Figures Figure 1: Tongue and groove wall plank sheathing beneath exterior siding Figure 2: Roof framing via attic access LOCAL EXPERTISE, NATIONAL EXPERIENCE. LEARN MORE AT DCI-ENGINEERS.COM Figure 3: Deflecting ceiling in kitchen below second floor Figure 4: Ceiling in northeast main floor bathroom LOCAL EXPERTISE, NATIONAL EXPERIENCE. LEARN MORE AT DCI-ENGINEERS.COM Figure 5: Typical main floor framing Figure 6: Floor beam supported by stacked stone and soil LOCAL EXPERTISE, NATIONAL EXPERIENCE. LEARN MORE AT DCI-ENGINEERS.COM Figure 7: Soil excavation that has undermined structural elements Figure 8: Deflected basement entry wall LOCAL EXPERTISE, NATIONAL EXPERIENCE. LEARN MORE AT DCI-ENGINEERS.COM igure 9: Porch at south sxterior of the House