GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Drying of under slab insulation

DanSilver | Posted in Green Building Techniques on

I am trying to understand moisture absorption of closed cell foam insulations.  I am currently starting to build a house  in Ontario and plan on insulating the under slab with an R20.  I can see that xps, eps and even spray foam have low moisture absorption qualities. What confuses me is drying.  EPS boosts that it dries more readily then XPS,  I see this over and over in many articles.  My question is how does the insulation dry under the ground? I would think that the only reason any of these insulations would get wet is due to hydraulic pressure forcing water into the products, with lack of air or any drying pressure how do they or especially EPS dry?  Can some one clarify this for me?

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.

Replies

  1. Tyler Keniston | | #1

    Dan,
    The 'drying' of EPS might be relevant to walls. Probably not under a slab. EPS is usually more permeable to vapor than XPS. I imagine that's all that's being said.

    Did any of the sources that mention EPS's ability to dry specifically mention sub-slab installations?

    Note that it will be a good idea to have a 'free draining' material (e.g. crushed stone) beneath your insulation, and poly on top of the insulation, prior to the pour.

Log in or create an account to post an answer.

Community

Recent Questions and Replies

  • |
  • |
  • |
  • |