Stone foundation - dirt floor basement... insulation?

lil_geekDecember 18, 2006

Has anyone insulated a stone foundation, dirt floor basement? A friend of mine (with a new house) suggested the spray foam insulation. I wonder if anyone has done it in an OLD house. It is supposed to be insulating AND protect from moisture.

I know the cost is more then anything else... but the other options is leaving the basement uninsulated and I wonder what that will do to the heating costs over time!

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Your basement isn't heated right? If it isn't it shouldn't cost that much in heating costs. Heat rises so the heat you pump into your living areas would go up, not down. Insulating your attic would most likely save you more money than insulating your basement. Also basements are insulated by the dirt so they stay the same temp. pretty much year round.

I WOULD NOT insulate the stone foundation with something that protects from moisture (on the inside). I would be afraid of water getting in and then getting stuck inbetween the rocks in the little spaces and instead of finding a way out freezing and causing damage.
Now, I am not saying this theory is correct, but I always think, if the moisture is getting in (from the outside walls) then it is most likely best it has a way to get out (maybe the inside walls)
If you want a moisture barrier maybe seal the outside and not the inside and prevent the moisture from getting in, in the first place.

    Bookmark   December 18, 2006 at 5:08PM
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First, you should be thinking about getting a vapor retardant layer down on the dirt of the floor. You are likely getting tons of moisture vapor rising from the soil. If you sealed up the stone foundation (not a good idea for other reasons) that moisture would get stuck inside your home, including inside your walls.

The first insulation task in an old house is getting attic insulation down. Then the next step is to do a heroic effort to seal up small infiltrating leaks around windows, doors, trim, etc. Depending on your plans for the walls, the next step is to consider what if any wall insulation you can install.

Finally, you might want to consider some under floor insulation between the first floor joists. However at this stage you need to think about whether reducing heat lost through the floor would result in your water pipes, drains, etc., freezing. These installations cana be protected but sometimes you have to make a compromise.

Now if you are mostly concerned about air infiltration through the exposed (and leaky) stones you might consider putting an infiltration barrier under the first floor joists. But for complete blocking of infiltration you also need to think bout sealing off air getting into your walls at the sills, this is more difficult (just picky, fussy work mostly) to do than the floors.

For the parts of the cellar that are subsurface and below the frost line, the earth keeps your cellar walls warm naturally as the earth pretty much stays at 55F, year round.

I have read about some concerns about direct sealing (ie with foam products) exposed field stone foundations because of the risk of damage to stones due to frost.



    Bookmark   December 18, 2006 at 6:54PM
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The heat escaping from your house is keeping frost from penetrating the stone foundation and heaving the stones. Never insulate a stone foundation so that it becomes as cold as the winter outside.

If you eventually want to insulate, the proper place for this insulation is outside. The spray foam is excellent, as it also protects from air infiltration. It does need to be covered with something, such as stucco, to protect it from sun deterioration.

Right now, your airy foundation is also keeping a lot of moisture from rising into your house, by blowing it away. Only seal and insulate your basement in combination with concreting the basement floor, to seal out moisture that rises from the dirt.

Molly has given good advice. Your best and first heat-keeping $ are spent in insulating the attic and in sealing all the cracks that allow cold drafts into your house. Fortunately both procedures are relatively cheap, as is laying plastic over the dirt in your cellar.

    Bookmark   December 19, 2006 at 8:19AM
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My friend had Her stone wall insulted with foam sheets and looks like stucco. It is glued to outside. They also put this black like tar stuff on outside for moisture. For temp she put plastic on dirt floor. But next summer having cement poured.

    Bookmark   December 19, 2006 at 8:57PM
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I was pretty skeptical. But the site I was reading was talking about protecting from water as well so I thought I would ask.

Attic is well on it's way to being insulated and the main floor is actually pretty draft free. The biggest cold factor we notice is on the floor on the first floor. I think we will try vapour barriering the floor and insulating the pipes and work at the sills.

Sort of an aside.... we noticed there are old 'windows' covered in with brick (not mortered and below grade on the outside)... woudl it help in the summer to attempt to dig them out and let some air flow?

    Bookmark   December 20, 2006 at 11:57AM
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Some of the advice above is completely contrary to current best practices. I'm aware this is an old thread, but a search pointed me here so I thought I'd mention this for the benefit of any other new visitors.

I would encourage anyone to spend some time researching. You'll find lots of conflicting advice, but in my experience the information available at is superior and backed up by actual scientific theory and research.

Here is a link that might be useful: Building Science Information

    Bookmark   December 21, 2010 at 2:13AM
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As one of Clint Eastwood's characters famously said, "Opinions are like a**holes. Everyone has one."

Here's how Building Science Corp.'s Dr. Lstiburek treated the rubble foundation on his own home.

    Bookmark   December 21, 2010 at 10:59AM
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Moisture in basements can come from a variety of sources. One of the ways we've dealt with it is to run a dehumidifier that self empties into a floor drain. It's made the basement much more usable.

    Bookmark   December 21, 2010 at 6:39PM
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Great site. There is a lot more on that site than repairing rubble foundations or as we say up here, field stone foundations.I saved it to my favorites and will spend a lot of time perusing it

    Bookmark   December 21, 2010 at 7:00PM
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One of the ways we've dealt with it is to run a dehumidifier that self empties into a floor drain.

I've used that method too. I grit my teeth every time I got the electric bill. I don't consider it a long-term solution.

    Bookmark   December 21, 2010 at 8:24PM
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been there done that i had the same prob in an old log home i used to have. we started with a full sheet of 6mil poly vapour barrier over the dirt floor after a week i could see alot of water droplets caught underneath it, after that ROXUL batt isulation between the joists and another layer of 6mil poly stapled up against the joists did the trick.

    Bookmark   December 30, 2010 at 5:34PM
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I've done it successfully with 2" of closed-cell polyurethane spray foam when there is not a serious water penetration problem and the stonework can be made clean and tight. The code required protection of the foam is not fire-rated; it is only a "thermal barrier" to avoid outgasing and smoke from the foam during a fire and is normally required to be 1/2" gypsum wall board. The use of intumescent paint must be shown to prevent the foam from reaching a certain temperature after 15 minutes of exposure to fire. Don't leave foam plastic insulation exposed; it's a killer.
Since you are insulating the basement you obviously intend to use it so you need at least a 3" think concrete slab over a vapor retarder membrane. Insulation under it would be a bonus which is usually only required by code in multi-family dwellings. It's OK to lower the sub-surface as long as the bottom of the foundation wall and central piers are not undermined.

If you have water infiltration issues use Worthy's link.

The temperature of the earth outside may be increased a few degrees by the unheated uninsulated basement but the only part of the earth that must be protected from freezing is directly below the bottom of the foundation wall but the wall should be deep enough to be protected.

Worthy is right about opinions.

    Bookmark   December 31, 2010 at 10:59AM
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