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

Convenient ignition barrier for EPS in crawlspace [edited]

John Ranson | Posted in Energy Efficiency and Durability on

I’m looking at putting 5.5″ of EPS on the concrete walls of my 4.5′ tall dry, conditioned crawlspace. The crawlspace is for utilities only, and will not be finished. It holds my air handler, ducts and plumbing. The crawlspace is accessed through a 2’x3′ (approximate) opening in the house floor. I was planning on attaching the EPS with adhesive.

Here’s my conundrum: What’s an good solution to meet the ignition barrier requirements for EPS foam in a crawlspace? I can get the EPS foam delivered precut to fit through the crawlspace opening and fit the wall height exactly. Cutting 3/8″ drywall, getting it through the opening, and moving it around in the crawlspace sounds like a pain. Is there a better solution?

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.


  1. Jon R | | #1

    Can you use a much easier "ignition barrier"?

  2. John Ranson | | #2

    Yes, I can use an ignition barrier.

  3. John Ranson | | #3

    I've updated the post to make it clear that I only need an ignition barrier. I'm still not sure of a good solution. The intumescent coatings that I've seen are only approved for spray foam.

  4. Expert Member
    Michael Maines | | #4

    John, if you fall under the IRC building code, as most places do, you can probably use one of the methods under R316.5.4, items 3.1-3.6. I would guess that 1 1/2" mineral fiber (rock wool or fiberglass) would be the simplest for you:

  5. Jon R | | #5

    I hate to see anyone use XPS, but Foamular XPS supposedly has an ignition barrier rating.

  6. John Ranson | | #6

    I don't think XPS is an option where the air in the crawlspace is exchanged with air in the rest of the house.

    1. Jon R | | #8

      Good point - either no ventilation (ie dehumidifier) or supply only ventilation would address that.

  7. Expert Member
    Dana Dorsett | | #7

    It might be cheaper/easier to just use a fire-rated polyiso (such as Dow Thermax) rather than generic EPS.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |