What to do with the uninsulated slab

[SolarAndWood]

The lower level walkout is a typical uninsulated 50s era slab. I have it completely gutted and will likely be in the house for a long time. It is about 1200 sq ft with a 50 ft wall of glass with decent SSW exposure in the afternoon. The only real limitation is the 7' 6" ceiling height. Any thoughts on how to best deal with it? Get the jack hammer out and put copper in a new insulated slab or put a layer of thick pergo down over a roll of the foam backer and use panel rads?

 

[pybyr]

I haven't used this stuff, but ran across it somewhere and it looked like an ingenious idea--- put a thin layer of polyiso insulation over your existing concrete floor as a thermal break, then this + radiant tubing, then a finish floor.

(broken link removed)

 

[SolarAndWood]

Something like that would probably do it although I can only imagine what it costs. I did a bunch of excavation and eliminated any possibility of water in the lower level. Given that, I almost wonder if a floor like one of the Pergo knock offs that has some, arguably minimal, insulating value and leaving the propane tanks full of hot water partially exposed is the way to go. I haven't figured out how hard I have to go after this as I haven't found a good analysis of how much heat I'm going to lose through the slab.

 

[DaveBP]

I can't think of any method of adding serious insulation over the existing slab that won't take away from what headroom you have now.

Will this room contribute a lot to your lifestyle? Will you spend a lot of time down there? Doing what? Workshop? Rec room? How tall are your family members? Do you like paddling around barefoot?
Those are hard questions to answer since the answers are not numbers or dollars.

If you can still get equipment in there, it won't take long with a rented breaker and a loader to yard that all out. Can you lower the grade more? Get some more headroom while you're at it.

It will be really hard to keep that existing concrete from being damp, especially in summer. Nothing like a warm, dry floor beneath the feet.

I would lean toward a new slab, but then it's not my money.

Couple or three inches of polyiso and vapor barrier beneath and around the edges. Pex tubing according to heat loss calculations. That WILL add up to some real money. It could be finish troweled well and painted for a low budget treatment that could be improved upon later. If you could lower the floor level while you're at it that would be a real coup.

My $.015

 

[SolarAndWood]

I can't think of any method of adding serious insulation over the existing slab that won't take away from what headroom you have now.

Will this room contribute a lot to your lifestyle? Will you spend a lot of time down there? Doing what? Workshop? Rec room? How tall are your family members? Do you like paddling around barefoot?
Those are hard questions to answer since the answers are not numbers or dollars.

If you can still get equipment in there, it won't take long with a rented breaker and a loader to yard that all out. Can you lower the grade more? Get some more headroom while you're at it.

It will be really hard to keep that existing concrete from being damp, especially in summer. Nothing like a warm, dry floor beneath the feet.

I would lean toward a new slab, but then it's not my money.

Couple or three inches of polyiso and vapor barrier beneath and around the edges. Pex tubing according to heat loss calculations. That WILL add up to some real money. It could be finish troweled well and painted for a low budget treatment that could be improved upon later. If you could lower the floor level while you're at it that would be a real coup.

My $.015

I think the lower level will have a big role to play, not the least of which is a nice view while loading the boiler. I have a jackhammer and a loader. And I even have a place on the property where I could use the slab as fill. There is one other complication, there are clay tiles that go through the slab every 4 ft from the uphill side of the house to the lower. Given the amount of water that moves through them, there must be springs or something uphill of the house. I removed an inground pool over the winter on the downhill side of the house that was blocking all the drainage and causing severe water issues on the lower level. Between the excavation and the 9 4x6 ft windows, the lower level is now bone dry. I didn't even notice that the sump pump was dead until I went to lend it to a friend of mine. I prefer gravity over pumps every day of the week.

That is where I keep coming back to maybe the best thing to do is nothing. Let passive solar do its thing in the winter and also expose enough of the propane tanks to heat the space directly. Then have a cover that can go back over the tanks in the summer when they are just warm for dhw. The big question is how much heat is really lost through the slab and does even a minimal insulator like pergo and area rugs put a good enough dent in it where it isnt worth it to do more.

 

[SolarAndWood]

The exterior of the foundation? or cut the slab back and do it on the inside? Do you have to go below the frost line or just below the slab?

 

[velvetfoot]

I was thinking of acid staining the concrete and using area rugs.

 

[SolarAndWood]

I was thinking of acid staining the concrete

I like that look and actually wanted to do that all the way through the house. Works well with passive solar, nice way to distribute heat, bombproof with the kids and dogs, etc. My wife gave me a lot of leeway in the design of the house which ended up pretty modern. However, she wanted hardwood floors and traditional windows. Seemed like a reasonable compromise.

 

[velvetfoot]

I guess then you could roll them up if you didn't like it.

 

[SolarAndWood]

The rugs definitely come out during the summer. That slab keeps the lower level nice and cool and cleans up easily. I don't think I'll even bother dropping AC ducts down there.