Polystyrene insulation in the basement

[PC1149]

How would you fix this in place?

I am thinking of putting it in first, then framing with metal, followed by drywall.

[Craig_md]

I am planning on doing the same, though with wood studs. There was an article in the Mar 2005 issue of Fine Homebuilding magazine where they suggested this approach, and used expanding spray foam for adhesive. I contacted one of the foam manufacturers and they said any non-solvent adhesive was also fine, in addition to the foam idea. Make sure to use low expansion foam though.

Good luck!

[em69]

Batt insulation is always better for this application since it fills the gap better and it is easier to work with.

Wood studs are preferable to metal.

[Craig_md]

No gaps to fill with this method. The insulation is applied directly to the foundation, and your stud walls are framed in front of it. The sheets of foam are butted up against each other and the joints taped. This method seems to be gaining popularity due to it's mold resistance, etc.

Wood vs. metal, won't get into that, everyone has an opinion.

[em69]

By placing your studs in front of the insulation, you are losing up to 8" of floor space.

[Craig_md]

Not gonna argue with you since you're obviously against this construction method, but with 2" of polystyrene, you lose exactly 2" of floor space over building directly against the foundation. Following other recommendations of holding batt insulation 1-2" off the foundation wall, you're in pretty much the same territory.

With that, I'm out of this discussion! This is one area where everyone has an opinion, and its next to impossible to get anyone to agree, and most methods when done properly work equally well.

[pracklam]

I assume you have a concrete foundation wall. You can get metal "Z" channels and screw to wall between the rigid insulation. This provides a flange for screwing the gypsum board on the interior side

[PC1149]

Sticking the foam to the wall and framing in front should produce a nice air pocket that will act like a thermal blanket.

It's the same idea as leaving a 2" space between the concrete wall and the dry-wall. Except this time the space is between the foam and the dry-wall.

[PC1149]

Where are you putting your vapor barrier?

[em69]

Vapour barrier is always installed on the warm side. Typically, this means installing it over top of the studs on the inside of the room. Then drywall is applied over top.

[Craig_md]

Where are you putting your vapor barrier?

I'm sure this will start a debate also, but the article I referenced in Fine Homebuilding magazine (and also the Building Science Corp. research/website) say that with this method, no vapor barrier is needed. The idea is to allow any moisture to diffuse, thus eliminating trapped moisture and potential mold growth, wood rot, etc. Look for the March 2005 issue of this magazine for the info. I believe the Building Science website also has an article about their recommended methods.

Good luck!
Craig

Edit - PC I sent you a pm with a link to the Building Science article

[TimE]

For fixing in place, I would recommend the right adhesive. There are some adhesives specific for mounting polystyrene to concrete walls, as well as other surfaces. I would strongly recommend using one of those.
I have done this, spacing pressure treated studs between the panels, then attaching the drywall to the studs. The resulting wall (one wall of a stairway) used only about an inch of space into the stairway.

In any case, I would recommend that you double check that what you are planning on putitng up meets code requirements for your area. I know that where I am, they require an R8 average for a basement, and the insulation I used on the stairs only provided R4, but since the rest of the basement was R13, the overall was just fine.