I've been noticing many frame designs don't show the size of the sill timbers. I have yet to find anything referencing sill beams in the books. Outside of beam strength perpendicular to the grain, how do you size your sill? The foundation wall is 10" the posts 7x10. What size do you make the sills? 8x8? 10x10? I would think either 7x7 or 8x8. This will give me a 2" lip on the foundation and an additional 2" for insulation thus providing a 4" lip for the SIPS. Any thoughts?

Thanks in advance,
Dan

Dan:
Each timber frame design can be different. Some frames sit on regular pressure treated sills with no timbers sills.
Some frames have conventional stick build first floor decks, with cut outs for the post to go threw the decking to the PT sill below, and therefore no timber sill.
It all depends on the actual design of the frame and if the first floor is going to be conventional stick built or timber framed.
If it's going to be timber framed then the sizing of the sill could depend on the floor joist connections.
In Jack Sobon's book "Build a Classic Timber-Framed House" he used a timber floor system for the first floor and he used 8"x 9" sills, that is 8" tall and 9" wide. These sills allowed enough space to create the pockets for the floor joist and other timbers to join them. His design was so that the exterior siding planks could be nailed to these sills and hang down a bit beyond the level of the sill covering the top of the foundation wall to shed the weather.
As mentioned each design is different and you'll need to size your sills accordingly, or don't use sills at all, depending on your specific needs.
Good luck with your project.
Jim Rogers

Thanks Jim. Good words of advice. Gives me something more to think about. My only concern with conventionally built floor would be the point loads on the internal posts.

Dan

Dan:
You said: "My only concern with conventionally built floor would be the point loads on the internal posts."
I would assume you meant "point load of the internal posts" on the first floor deck from the second floor or roof system above.
Which is true and you should be concerned. If you do have internal posts they need to be properly supported all the way to the foundation or cellar footings. As with the wall posts the decking can be cut and the posts bottom would be trimmed to fit around any rim joist so that posts will fit properly and be supported properly.
To do any internal post you can either cut the decking and extend the post threw the decking to some proper supporting substructure, or block up the decking from underneath and support this blocking properly so that the post point load is transfered again to the foundation or cellar pillar footings.
Proper planning will prevent poor performance.
Good luck with your project.
Jim Rogers

Jim,

Correct assumption. I could think of multiple ways of doing it but wasn't sure how it was generally done. I'm leaning to the more traditional method but have not ruled out standard framing.

Thanks again for the thoughts.

Dan