Insulating exterior and interior of below ground concrete block foundation
akyeti
| Posted in Energy, Heating & Insulation on
I have a concrete block foundation built into a hill to provide a daylight basement. On the outside there is 4 inch of Styrofoam SE 25 psi 4′ X 8′ sheets. On the concrete block is Bituthane Membrane. What I want to know is how should I insulate the interior concrete block? The south concrete block wall is the daylight side and should I insulate both sides of it? Thanks for your time.
Replies
First thing to apply is the location and heating/cooling zone.
between the foam board and membrane, your buried wall sounds moisture sealed and insulated to R20.
The other wall should be insulated and air sealed, but there are options. You can put more foam board on the outside, or rigid rockwool, or other choices. these need to be covered to protect from damage by rocks, critters,.....
Inside walls that are insulated and buried on the outside need care to not install another vapor barrier that can cause issues. but a nice framed wall with rockwool can provide more insulation and sound deadening. (and be covered with drywall for a nice finish on the inside)
For the south wall that is currently block, do you have plans to finish or cover the outside? the location and characteristics of air sealing, vapor barrier, and insulation do depend on where you are.
Thanks for reply Uncle Mike. I will be putting a cover over southside but haven't chosen yet. It did have 1 inch of Styrofoam covered over with T- 11 that was painted. It was built in 1962. I need to pick what to put on as cover (stucco, brick, wood or engineered product). As it will be the exposed side to wind,sun and rain what would be a good choice? Looking at Styrofoam as insulation.
It is all up to your tastes and budget.
If you live where the snow flies (meaning the primary utility use is heating, vs air conditioning) then this wall would be good to treat as an above ground wall. (meaning it needs insulation and vapor retarder to avoid condensation inside the wall or insulation)
4 inches of XPS would be ok on the outside, but then the finish of your choice over it. There are stucco type coatings sold for application directly over the foam. this could work if you like the look.
How does the wall above look? If it does not extend past the south block wall enough to allow water to drain past your wall finish, you might be better off putting insulation on the interior of the block wall. (and a good time to make sure the inside of the rim joist of the floor above is sealed and insulated)
Hello. The wall above is a wood lap siding of some sort, or a fiber cement product. Still deciding what is less cost for product value. (bang for buck) I am in a northern 4 season climate. The roof above has a 2 foot over hang. Enclosed is south side of home.Thanks for reply