Insulating PTW foundation/retaining wall
HO/GC here… SE MN…OK, pressure treated wood foundation is up and plumb, rest of framing starts this week. This is one part of an addition onto an existing 20X24 cabin.
Here’s the deal. Two of three new addition walls act as both foundation and exterior walls, and the third also acts as a partial retaining wall. 12 foot .60 treated 2X8s on 16″ centers from footing plate all the way to quadruple top plate. Sheathed with PT plywood first 8 ‘ up from footing plate, regular exterior plywood top 4’.
Two side walls are 14′ long, long wall (the one that’s also acting as a partial retaining wall) is 34′ long and is backfilled to about 6′ from top plate. 2′ crawl space underneath 2X10 fir joists on 16″ centers, topped with Advantech subfloor. All exterior walls will get Typar and siding.
There are two plywood sheathed interior shear walls between the long wall and the cabin keeping the long wall stiff and plumb.
There are two more wings being added, the walls for which will be framed on TOP of the deck, as the deck for these wings is framed conventionally on top of the foundation walls.
Get the picture?
There is open area from the crawl space backfill up through the stud cavity all the way to the top plate…since the foundation/exterior/partial retaining wall was built before the deck was on, the subfloor ends at the inside face of the studs, on a band joist that is nailed to the studs…cross joists are on hangers.
I have already friction-fit blocks of 2″ rigid foam over the dirt between the studs in the crawl space to protect the FG insulation from potential vertical moisture migration, and plan to seal the crawl space bottom and interior sides with 6 mil poly.
Question is:
Should I also fit blocks of rigid into these stud spaces flush with the subfloor to create a VB between the crawl space and wall stud spaces? Or would an un-interrupted cavity filled with FG be better?
I suppose an option is to expand foam the whole thing but lots of $ for a 7 1/2″ cavity.
Edited 10/28/2003 10:50:53 AM ET by johnnyd