Context
I am conducting a major renovation of my home in Western Washington State, USA, and there are going to be seismic retrofit expectations concerning the foundation and mud plates when I get them inspected. Most foundation retrofit videos seem to demonstrate drilling new bolts through the 1.5" plate, and the job is done. My home is a little different.
What makes it a challenge?
I have a late-1960s single-story/rambler with a pier-and-beam construction, which is a thick and rigid tongue-and-groove (cardeck) subfloor over 48" on-center 4" and 3" beams and piers. There are no typical 24" or 16" floor joists, and the way the flooring system ties into the foundation is variable. It has 4 different structural profiles across its 6 exterior walls. For this question I will be referring to these as profiles A through D.
Profiles
Profile A: The foundation wall contains the 2x4 mud sill, and the floor beams rest directly on both the sill and the foundation. There is no rim joist, but there are occasional scrap pieces of flooring used as blocking for supporting siding or crawlspace vents. There is approximately 13.75" between the top of the wall's bottom plate and the concrete beneath the mud sill.
Profile B: The foundation does not directly support the floor structure. The concrete is extra high, and the subfloor is laid directly over the mud sill. To compensate the lack of support from the foundation, concrete pads and piers are placed close to the foundation and directly support the beams. There is approximately 4.5" between the top of the wall's bottom plate and the concrete beneath the mud sill.
Profile C: This is similar to profile B, except in the perpendicular direction. Since the beams supporting the floor are running parallel to this foundation wall, the foundation acts as one of the beams and directly supports the ends of the subfloor planks.
Profile D: This is similar to profile A, except in the perpendicular direction. Similar to profile C, the joists run parallel and the ends of the floor are directly supported. However like profile A, the foundation wall is lower. Unlike profile A, there is a rim joist here.
Possibilities considered
For profiles A and D, the possibility of using retrofit foundation plates and shear transfer ties feels like the right option.
However, notice my mud sill is positioned on the outside of the foundation. These retrofit foundation plates appear to fasten to the inside edge of the mud sill rather than to the top, and I would need to cut out 1.5x2 inches of concrete all the way around my foundation to make those work. Side note: wouldn't that make my foundation less seismically safe? And regarding the shear transfer between the mud sill and beams/joists, I have struggled to find the right product to accomplish this.
For profiles B and C, my gut instinct is to use the typical drill-and-bolt method through the bottom wall plate using expanding fasteners or something similar. However, most bolts I am finding are 5-6" long. The wall plate, subfloor, and mud sill add up to 4.5" on their own.
Questions
Question 1: For each profile described, what methods would you recommend for seismic retrofit, and why? This is my main question, and the others have been unearthed while trying to answer this one.
Question 2: If we go with bolts for those shorter areas, how long do they need to be?
Question 3: Where is shear transfer required in my case? I would guess between the beams and mud sill, as those are only toe nailed and could slip off. And my other guess is between the rim joist and the mud sill. But what about the bottom plate of those walls transferring through the subfloor and to the beam/rim?
Question 4: How do I calculate that I have adequately reinforced my foundation using any of these methods?
Closing statements
I will also be getting in touch with my local building inspector about this. However, the inspector isn't my professor, therefore I would like to collect some knowledge from this community and know my options before engaging in those conversations so that they can be productive for both of us. Hopefully we can create a reference for others along the way.
I can measure and photograph different areas if required to get to the answer.
