0 Helpful?

Is it necessary to tape joints in under-slab insulation?

I'm putting recycled 4" XPS under my slab. Zone 6. Do the joints need to be sealed with anything? I'll put poly on top, under the concrete.

Asked by stephen sheehy
Posted Aug 11, 2014 9:08 PM ET
Edited Aug 18, 2014 5:57 AM ET

Tags:

5 Answers

Select your preferred way to display the comments and click "Save settings" to activate your changes.
1.

Nope- the taping would have negligible value at best. The amount of thermal bypass air movement under the slab is miniscule, and the poly layer makes it air & water-vapor tight.

Answered by Dana Dorsett
Posted Aug 12, 2014 11:10 AM ET

2.

Thanks, Dana-That's what I hoped was the case. Your explanation makes sense.

Answered by stephen sheehy
Posted Aug 12, 2014 11:19 AM ET

3.

You doing one layer of 4" or 2 layers of 2"? Good to have staggered seams.

Answered by Dan Kolbert
Posted Aug 12, 2014 8:42 PM ET

4.

Dan-we're using 4".

Answered by stephen sheehy
Posted Aug 13, 2014 9:21 AM ET

5.

I used 3" XPS under my basement floor and didn't tape the seams, we did however ensure we taped the seams of the poly vapor barrier extremely well.

Answered by Anthony Hughes
Posted Aug 18, 2014 12:54 PM ET

Other Questions in Energy efficiency and durability

How does efficiency in a mini-split vary over various operating levels?

In Mechanicals | Asked by david jensen | May 3, 16

Smart vapor retarder over open-cell SPF on underside of roof in Zone 4 (Washington, DC)?

In Energy efficiency and durability | Asked by Elizabeth Hilder | May 5, 16

XPS brands: Dow; Owens Corning; Pactiv/Kingspan?

In Energy efficiency and durability | Asked by Bill Daugherty | May 5, 16

Improvement on the Lstiburek Ideal Double Stud?

In Green building techniques | Asked by Burke Stoller | May 6, 16

Insulating behind tower/tub

In General questions | Asked by M S | May 5, 16
Register for a free account and join the conversation


Get a free account and join the conversation!
Become a GBA PRO!