Timber Frame Post + SIP + Sill Connection Question
Hello,
I am working on a Timber Frame that will be enclosed by SIPS. I plan on having a basement so I will have a foundation wall with mud sill and a conventionally framed 1st floor deck (with a rim joist and floor joists bearing on the foundation wall). Given all that I have read here about heat loss through the rim joist (I am in a cold climate, Idaho high desert), I really want to position the 8″ x 8″ posts in such a way that the SIP can also cover the rim joist. Normally, a timber frame post will sit on top of the decking and be supported underneath with (wood) blocking. The problem is that my site also has seismic requirements and my gut tells me that I really ought to have the post bearing (lower and more directly) on the foundation wall (and mud sill I assume). I may employ pilasters or “bump outs” on the basement walls to get the full bearing but I really want to figure out a detail that would allow me have the posts be flush with the outside of the rim joists. I have an idea (with angle brackets against the post) that makes sense but it’s not “buildable” because one needs to complete the 1st floor deck before one can raise a Timber Frame bent. Here are some questions:
-Could I use a fabricated steel raised platform to bring the bearing surface up to the top of the rim joist?
-Could I use a precast 8″ x 8″ concrete block to bring the bearing surface up to the top of the rim joist?
-Is blocking strong enough? Should the grain of the blocking be parallel (like the post above) or could the blocking grain be perpendicular since the area bearing weight on the rim joist will be perpendicular?
Also, I am obviously going to have the whole design reviewed and stamped by an engineer (as required) but I know there are a lot of savvy designers here that may have found an elegant solution to this problem. Most of the nice “clean” details I have seen of a post interface have been with a slab-on-grade type foundation. I also know there are rim joist “band SIPS” that can be used to wrap around a rim joist. And maybe notching out the post a bit is a reasonable solution once I crunch the numbers on the 8 by 8 or 64 square inches of bearing surface capacity of Douglas Fir.
Sorry for the part energy efficiency question to maximize the SIP coverage and the part engineering question… I am just trying to find a solution that solves both.
Thanks for all the super knowledgeable folks here who contribute their knowledge.
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Replies
John,
There are lots of options here, and you may want to consult an engineer.
It seems to me that the most straightforward approach would be to raise the timber frame without any floor framing. That may be difficult, but it's still possible -- especially if you can get a crane on site.
If needed, you could certainly build a temporary floor inside the basement foundation (used only to facilitate the raising of the timber frame); once the frame is raised, the temporary floor could be dismantled, and the permanent floor framing could be installed (using joist hangers and a rim joist installed on the interior side of the posts).
I'm attaching a few details below to spark ideas.
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Hi, Meet with the engineer you plan to use for the structural design of the building. They will have standard details they have figured out for your issues. So start form their plans. Using the standard details will save you money on engineering time and the timber frame contractor erection time.
Make sure the SIP you plan to use has an approval report indicating it can be used in you seismic zone. SIPS need this to be used in higher seismic zones, they are only prescriptively approved in low seismic zones.
Your SIP will need to be directly over and attached to the foundation and sill plate for proper transfer of the seismic forces. It can't easily go out side of the Rim joist. You could ledger the floor system off the stem walls and have the floor system be flush with the top of the stem wall, eliminating the rim all together.
The timber frame will support the gravity loads of the building. Transferring the gravity loads thru a floor system is very common and will be designed by the engineer. Blocks should be set grain vertical so they won't shrink as they dry.
Again get the common details the timber frame company and engineer use. The have used the details before and can price the job based on those details. You can work with them to modify them for better performance, or if too much resistance to change is encountered then you can find some one else to work with.