Extruded Polystyrene Insulation

In previous posts the advice I was given was to use Extruded Polystyrene Insulation in my basement walls.

I see at the big orange box store they have 3/4 -2x8 FOAMULAR Extruded Polystyrene Insulation with an r value 0f 3.8. Can I double this up to give me more insulation and r value or or is there no extra value in place two sheets between the wall studs?

They also have 1 1/2 FOAMULAT INSULPINK extruded polystyrene on sale, but Im not sure what the difference is between the two products and if this is exactly what products were that you guys advised me to get.

Thanks

Tom

Generally R-values are additive; I would expect the 1 1/2" stuff to have an R value of about 7.6. I'd prefer the 1 1/2" myself if I had that much space to fill, to eliminate cutting and pasting. An important consideration in installing this stuff is to be sure there are no gaps around the edges (next to the studs, etc.) which would allow air to leak around the insulation.

If you go to a full-service lumberyard, you can probably find foam in any thickness you wish. Pick the one that give you the insulation factor you want or need. You may find that paying someone to foam-in-place comes out about the same price, and then you'd not have any gaps at the edges, around outlet boxes, or pipes.

The other way not to get gaps, in a basement situation, is to glue it to the walls & then frame inside that.

Today I got a email from Ownes Corning that stated they recommend that I do not use polystyrene in a below ground application, but did not specify why. I sent a reply back for more information, but have not heard back yet.

ctkeebler said:

Today I got a email from Ownes Corning that stated they recommend that I do not use polystyrene in a below ground application, but did not specify why. I sent a reply back for more information, but have not heard back yet.

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are you sure they are not refering to outside below grade ?

My question to them was about interior below grade. Ill copy the email they sent and post it here.