Foamboard and creep deformation
I have been trying to find a way to insulate a brick ledge on the north side of my home. I am planning a large insulation upgrade to help get my floor heat somewhat working and seal up the house some.
The hydronic slab is not insulated as the seller claimed, and the hydronic system has too many losses to heat the home effectively or sometimes even at all. I plan to put 4″ of Roxul, 4′ down around the slab exterior, and use 4″ of XPS starting at the sill. This should raise the R value of my walls from 10 or 11 to about 30, and the slab edge from about .8 to 10. I am also planning on sealing up the ceiling and adding blown in cellulose up there for at least R60
The only reason I’m even considering touching the brick wall is it is the north facing side of the house and has at least 60′ linear exposed slab edge and 60′ of walls that are only R11ish.
If my brick wall is ~17 courses tall, and an average brick weighs 5 lbs with ~ 24 sq. in of area, the pressure exerted at the bottom of the stack would be only 3-4 psi plus mortar. Owens doesn’t recommend using the foam under a brick wall due to creep.
If this is truly a concern, why do people regularly put foamboard beneath slabs, and sometimes even footings?
The compressive weight on the foam would be way higher in the footing situation and I would think cause long term creep.
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