Basement insulation and air sealing question

I am insulating an existing basement. Assuming that the exterior drainage issues are taken care of, here's what I would like to do.

Floor
1. Lay 1"EPS foam on the slab, tape the seams.
2. Place 1/2 inch plywood subflooring, screw down with concrete screws.
3. Place cork flooring.

Walls
1. Attach by adhesive, 3.5" of EPS foam on the CMU walls, tape the seams.
2. Frame a wall to attach drywall by using 2x lumber
3. Drywall.

The part I am not so sure about is the tape between the seams of the EPS foam. Does it need to be good tape like Siga or does just need to hold the foam together? The goal is to make the envelope relatively tight 1.5 ACH 50. I think I have the airtight layer of the above grade framed portion and also the joint between the basement and the wood framed structure figured out. How much do I need to worry about the CMU walls and the concrete slab being airtight?

Asked by Roger Lin
Posted Thu, 03/21/2013 - 22:23

Tags: Green products and materials

1.

Roger,
First of all, EPS is hard to tape unless it has foil facing.

Second, you don't have to worry too much about air leakage through your CMU wall. Even if you don't manage to get airtight seals between your EPS panels, it doesn't matter very much.

Third, if you want to address the (small) thermal penalty caused by the seams, you can install your EPS in two layers, and stagger the seams of the two layers so that the seams aren't continuous all the way through.

Answered by Martin Holladay, GBA Advisor
Posted Fri, 03/22/2013 - 06:03

Edited Fri, 03/22/2013 - 06:04.

2.

Martin,
Yes, from my experience EPS is a pain to tape. That's right, I could do it in a staggered fashion. Great tip.

Thanks
Roger

Answered by Roger Lin
Posted Fri, 03/22/2013 - 09:23