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Old 01-21-2014, 06:35 PM   #1
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Basement question

Finishing my basement and planning spray foam for the exterior walls. In Cleveland the frost line is about 3 feet, if that's the case why not just foam the top 4 feet if the wall and leave the bottom 5 feet bare cinder blocks since those would be insulated from the outside by the soil?

I know I will get bashed but please be easy on me, I'm trying to learn here. Why does the whole wall need insulated and not just the top few feet?

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Old 01-21-2014, 06:57 PM   #2
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It's not about frost depth. I'm not sure where you are located, but I doubt you'd ever see 3 feet of frost where you are and if so not for long. Here, code dictates we go 48" down to be below frost & I've never seen frost below the first 3-4" of soil.

In any case, you are looking to keep heat in and cold out, so to to do that efficiently, you need to insulate the entire wall. Since you're in the basement, you should use closed cell foam as open cell absorbs moisture like a sponge.
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Old 01-21-2014, 07:01 PM   #3
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That's a good question. In Ontario it used to be code to only insulate to the frost level but a few years ago they changed it to the entire height of the basement. Then a couple years after that they upped the R value from 12 to 20. It is better and the more insulation the better.

If you are going through the trouble of doing the top bit then the whole thing is that much better. It shouldn't cost you too much more. I've seem people spray the floors too. Foam is good at blocking out the moisture from the cinder blocks. Make sure all you electrical and plumbing is done first because it is a pain to do after.
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Old 01-21-2014, 10:16 PM   #4
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Thanks! I know if I use the diy green stuff my 1500 sq ft of wall space at 1" thick will cost about $1800. Going to get a quote or 2 from a pro and if it's not much more I will go that route. Any idea what a pro company will charge and how this they will shoot it? Thanks!!!
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Old 01-22-2014, 06:36 AM   #5
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SPF pricing is all over the place.

Get a couple of quotes and know that the SPF quality from a full rig should be better than the froth paks by far.
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Old 01-22-2014, 05:47 PM   #6
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IMO, insulate the whole wall; as snow/ice melts and follows your foundation wall down, making it the same temp as the melt water, or surface water;

Granted, the earth is warmer the lower you go; 6' down it is +-10-11*F warmer than grade temps;

You certainly don't require the same amount of R-value as above/just below grade. If the wall/slab is at 55*F you would still lose R-value by warming it to room temp rather than have it start warmer right away as the foam is there and thick enough to insulate showing 70* rather than losing R-value to gain the 15*.

Another consideration is the fb would stop warmth from leaving at the slab/wall joint, a little hit in resistance;

Notice the figures for different depths of perimeter slab insulation;

The heat loss in most basements is enough to warm the footings enough to not have frost heave; http://www.buildingfoundation.umn.ed...timum-main.htm

The DOE has to set a limit or design for insulating basements. If SPF, the installer could coat that wall portion with less; as long as the cavity insulation makes up for it to meet minimum code, check with local AHJ.

PS. if with a walk-out basement the slab/lower wall could still be at winter temps during the spring weather (due to 2 month lag from being earth-tempered) giving condensation there;
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