Insulation of apron

[bharvey]

I have a dilema. I am in the process of having a 23x44 shop built (two stories, 650sqft up for office, theater, apartment... later) in Salt Lake City. The 8" thick stemwalls have been poured 6' deep and the framing is just about complete.

The builder didn't poor the floor, he wanted to frame and sheath so he could easily heat the floor during the pour. (Cold and snow all winter long this year)

I work out of the country about 1/2 the time and he backfilled without insulating the exterior stem wall because it wasn't included on my plan. (really my problem).

Beacause of grade considerations the floor will be lowered 2.5' below the top of the stem wall. The stem wall will be 8" above outside grade. this 8" thick stemwall with 2x4 construction will result in a significant protruding shelf/ledge on the interior. Finished height of first floor will be around 11.5'.

My plan to deal with the lack of the exterior insulation and the ledge at the same time -

1. Insulate beneath the slap with 1-2" of foamular.
2. Insulate the interior stem wall before the pour. this will create a "floating slab" still tied to the stem with rebar though.
3. After floor has cured, build a 40" tall false wainscoted wall to allow for insulation of the 2.5' stem wall. Wall will be surfaced with MDF and trimmed with MDF milled by me. This will make the shelf at the 40" mark about 6" deep.

Insulate under slab - check
Insulate between side of slab and stem wall, preventing frost permiation - check
Insulate stem wall AND push inconvenient ledge up to 40" mark, making it attractive and staying out of the way of installed benches and cabinets - check

I really want to make the right decisions now, given the missed opportunity to insulate the exterior. I think it would be expensive to excavate, clean, insulate and backfill again.

Is this the best course of action?

Any help would be appreciated.

bkh

 

[ju539]

Maybe I missed something, but...how about putting the 40" AFF ledge on the outside of the building with some flashing over the top of it and under your siding and make the interior wall flush???

Just a thought, Twobit

 

[sneezer41]

Sounds like you have it right to me. Very similar to what I have done. You might want to think about buying some barrier pex and tying it to the mash in case you ant to try radiant heat later. Id have this and it is great. I ran foam between the slab and the apron[is this what you are asking about?] having the door hit the apron so it closes on cold and does not have heated floor outside, or melt issues. I always intended to trim it out with something but never have. I have done 2 floors, this radiant one, and a previous non radiant, with no ins under, but insulated inside from the wall, and both are much better than the usual practice. I wold not bother tying to the walls, as the concrete is not going to go anywhere, and it would seem to me that the differential movement is more likely to cause trouble than anything else

 

[sneezer41]

woops, 'mesh' not mash 'want to try' not ant...

Also for clarity, the radiant floor is insulated under, previous one wasn't

 

[bharvey]

Ju539 - The walls are already framed and sitting on the apron.

Sneezer41 - Thanks for the confirmation. I would really like hydronic heat, but not thrilled with the cost of quality material. Did you do it yourself, cost per sqft? reliability? vendor? boiler vs water heater?

I like the idea of putting in the pex, just in case.
thanks again

 

[5wndwcpe]

Definately go with the PEX, even if you don't install the boiler/heater until years from now. After the slab is poured, you won't have that option.

As far as the ledge goes, I have very nearly the same situation in my shop currently. My walls are 2x6's sitting on top of block which result in a ledge running all the way around the shop. The goofy thing is, because of the exterior grade, (garage is cut into a hill) my block runs from 3 courses all the way up to 8 courses and back down again. If I were to leave it as is, the ledge would be all over the place. My solution is to build another 2x4 stud wall, sitting on the block and stepped off by 1". I then run furring strips secured to the block with 1" DOW board in between the strips. This set up allows me to insulate the block with the rigid insulation, run the sheetrock all the way to the floor, increase the insulation by fitting R-30 in the walls and best of all, I can face-nail the Romex to the 2x6's before building the 2x4 wall, eliminating the need to drill a bunch of holes for the wiring.

 

[flesburg]

I really like for my floors to sit on the "stem" wall, not floating down inside it. Even with rebar tying it to the walls the floor can still settle. Is it too late to rethink and pour the floor on top of the ledge? Put 1/2 inch plywood inside the 2x4 wall, line it with sheets of aluminum for moisture barrier, and pour the floor on top of the concrete wall.