Insulating Above Grade CMU Stem Wall with Under Slab Insulation

[TracerRound]

I am looking for some clarification on the correct way to insulate a 4ft CMU stem wall where the rear of the building will be below grade about 3.5ft of it and the front (garage door side) will be almost all exposed. I have seen a few images online but I did not find one where the slab was poured just above the footers instead of near the top of the stem wall.

One I found on BuildingSciense.com (ignore exterior insulation):

This is my crude sketch on what I am thinking is ok (vapor barrier between slab and 2in under slab foamboard):

 

[TracerRound]

This may better belong in the General Garage Discussion, if a mod sees this

 

[TracerRound]

Any input on whether the insulation location should change based on the slab being below the top of the stem wall?

 

[Rusted Nut]

Your sketch will work, and is a common method for this. You can build a furring wall on the edge of the slab for a finished room if you want. If you live in an area subject to termites, the code allows you to **** the slab to the foundation wall, and place rigid insulation on top of slab. Check with local building dept.

 

[BobnCO]

I think your sketch is correct. FYI there is a Z-channel system you can use on the exposed wall. I have done two basements this way (one commercial one residential) and it is nice. I got the Z channel from drywall supply house and foam from insulation supplier (may be the same for you).

 

[finn]

The foam should be covered to protect it from UV and physical damage. That means a stud wall inside the concrete.

 

[billconner]

If you follow code, no foam exposed to habitable space - 1/2" drywall or 3/4" wood or equal.

 

[BobnCO]

That’s what the Z channel is for, attaching over foam; typically finish with drywall, but in a garage you could do 4 x 8 siding, CDX, OSB.. wtf

 

[TracerRound]

Thank you all. Sounds like I need to cover it whether it is inside or outside the stem wall. I may need to look into putting the foamboard on the exterior and cover it with something.

 

[C-S-H]

Before getting too deep into the insulation and other details you should consider the structural design of the block wall. You have both earth pressure and a hinge in the wall that will require you to properly reinforce both the block wall and the footing. Your footing proportions are way off for the job it needs to do. Do not use concrete wall or footing proportions from the Building Science site as a guide.