Insulating a Foundation

[CadAndy]

Some contractors have suggested or actually
adding styrofoam around and beneath a foundation
for insulation. From what I understand this is
considered a vapor barrier which causes condensation
to build up between the styrofoam and foundation
walls.

Over a period of time especially in colder
temperatures won't this damage the foundation?
I can just see a crack in the foundation and getting
some type of moisture within the crack and then
freezing. That crack might no become a hole or
even a larger crack. Any comments about this method?

 

[Focht3]

Do a Google search on 'geofoam' - I think you will be overwhelmed with the number of hits!

The use of Styrofoam for insulating foundations is actually quite common. Hopefully some others will give you some pointers on the "do's and don'ts" of this material. (My use of geofoam for insulation has been limited to insulating freezers in areas where the water table is pretty deep.)



Please see FAQ731-376 by [blue]VPL[/blue] for tips on how to make the best use of Eng-Tips Fora.

 

[CadAndy]

This looks similar to SuperiorWalls where the
insulation is within the concrete.

This part I understand but when applying
vapor barriers they do not recommend applying
the vapor barrier to the exterior a building.

Thanks for the info though

 

[CarlB]

As Focht3 mentioned, insualting foundations is very common. See

http://www.huduser.org/publications/destech/desguide.html

for a design guide. In slabs and foundations I belive the moisture migration tends to be from outside (the ground) to inside, the opposite of walls in cold weather, so a vapor barrior on the outside shouldn't be of concern.

 

[CadAndy]

I did some more checking into the Vapor Barriers
and it is NOT recommended that you place a
vapor barrier or vapor retarder it most situations.
The ACI 302 committee only recommends a retarder of
0.25 mm thick to protect from moisture. There are
three sites below that will explain it in more
detail.

The last WEB site explains the Vapor retarder in
great depth.

http://www.doityourself.com/hvac/vaporbarriers.htm

http://www.handymanwire.com/articles/vaporbarrier.html

http://www.lafargecorp.com/ttt_vbvr.htm

 

[swBausch]

If the vapor barrier is the only thing between the moist air and the colder area , that is the problem. The windows of your car are a "vapor barrier" that can be as warm as the moist air, or as cold as the outside, depending on the defroster being on/off.


If the vapor barrier is between the insulation and the moist air, that's where it's supposed to be. 'Nuff said.

It may help to draw a diagram of the "cold air",insulation, vapor barrier, and "warm moist air".

There is plenty of dispute regarding the value of vapor barriers. Not as bad as politics or religion, but give it time.

 

[RockEngineer]

Here is some more information from US Dept of Energy on the controversy of insulating or ventilating crawl spaces and insulating slab on grade foundations.

http://www.habitat.org/pdf/ENV8-FoundationAndFloors.pdf