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

Mini crawl space

user-228058 | Posted in Energy Efficiency and Durability on

I have decided to convert a piece of my timber frame barn into living space on my new home.( the barn is there) what I would like to do is elevate a 2x 8 floor above the existing slab. This would hanger onto the existing perimeter grade beam that sits on top of the concrete stem walls. I would set the floor 1.5″ higher than the grade beam to create a thermal break with a narrow ripping of eps. So I would end up with about 10 inches beneath the floor assembly. So I am considering the following options, panelizing the floor and preinstalling sheathing or perhaps some kind off wrap underneath( prior to installing) This would allow me to dense pack the floor from the top creating a unconditioned crawl space above grade if you will. I would block off the opening from the balance of the barn/ garage using a combination of rigid foam and p.t. Lumber. I could install vents here if needed.
Another option would be the same frame assembly with a couple layers of foam directly on the slab and leaving the floor assembly conditioned if you will. Transitioning the foam vertically would require spray foam to make the rim assembly adequately insulated. Another option would be to build up the layers of foam high enough to pour a slab . Say about 6 or 8 inches of foam then 4 inches of concrete, then I would need to insulate the grade beam creating some sort of insulated base trim. This brings me to how to insulate the timber frame. But I will save that for another post…. thanks all in advance.

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. user-6184358 | | #1

    Hi, I don't see how you could meet the building code access requirements for access with a wood framed floor. Unless it is wood sleepers attached to the concrete and foam. I have seen mice get under floors made of wood sleepers. BAD
    I think your idea of the foam and concrete is the to go. If you wanted to reduce the foam you could go with a layer of sand or gravel then foam then concrete. With the concrete you could add radiant heat in the floor.

  2. Expert Member

    I brought up similar concerns with Steve Baczek, who built a house on a short (crawl) space quite similar to what Scott is proposing. Here is a link to the discussion. I don't know if his explanation would fly with most inspectors.

  3. Jon_R | | #3

    EPS foam then plywood (no joists) makes sense to me. Gravel under the foam if you need leveling or more height.

  4. user-228058 | | #4

    Tim, the code issue rises as it is a large amount of square footage even if it is a smallish volume of space.? . Jon , they did a article in JLC with foam and osb as a alternative to a slab. Interesting, I will contemplate this . My first thought is this plywood or osb over foam approach would negate the odd detail of concrete meeting the side of the timber grade beam. I will register for the GBA pro and read the article referenced by Malcom. Thanks all...

  5. wisjim | | #5

    This past summer we raised the floor of our sun room almost 2 feet. It was a couple of steps down from the rest of the house and has a tiled slab floor. We decided that joists would be complicated to insulate and would leave an inadequate crawl space. We found some good used hi-density EPS and filled the space with it, then 2 staggered layers of t&g waferboard subfloor, topped with linoelum tiles. It went together well and we are very happy with the result.

  6. Expert Member

    What is it like to walk on? Does it feel cushioned in a way a framed floor doesn't?

  7. user-228058 | | #7

    Jim, how were you able to identify that the eps was in fact hi density at the reclaimer? I've had more experience using XPS and polyiso. Were you able to visually see a difference in the bead structure or such?

  8. user-6184358 | | #8

    What is a timber grade beam? Is it the wood attached to the concrete foundation?

  9. GBA Editor
    Martin Holladay | | #9

    I vote for installing a horizontal layer of dense EPS, as thick as necessary for insulating purposes or for establishing the desired height, followed by a new 4-inch slab. (A layer of sand could be included if needed for height.)

    If the EPS is thick, installing a plywood subfloor rather than a slab would be tricky, because the needed TapCon screws would be very long. One possible solution would be to install a double layer of 3/4-inch plywood on top of the EPS, staggering the seams. If the two layers of plywood were screwed together, this approach prevents "potato chipping."

  10. wisjim | | #10

    To answer some questions about our new floor, the EPS was obviously denser feeling and finer grained than some regular density EPs that I also had on hand. We could walk on it without making footprints or other markings in it. We covered it with two layers of 3/4" tongue and groove OSB, with joints staggered, fastened together with 1 3/4" screws, so that the OSB is floating on the foam. We like some of the real linoleum products but didn't want to hire a professional to do a center seam which would have been necessary if we used sheet goods, so we used the Marmoleum "click" panels which are nearly 12 by 36 inches (not quite that big due to metric sizing). Using these tiles made it easier to fit around all the posts which meet the floor on three sides of the room. The floor doesn't have any bounce or softness to it and doesn't feel as unyielding or hard as the old tile on slab floor did. It doesn't feel as "bouncy" as the frame floor in the adjoining living room area. We are quite pleased with the way it turned out. We raised the floor over 22" using the foam.

  11. user-228058 | | #11

    Tim, the timber grade beam is a 8x8 white pine beam that sits on a 2x8 p.t. Sill plate. The timber frame tenons down into the timber beam. I believe this style comes from when , in past centuries the foundations were dry laid stone..

  12. user-228058 | | #12

    I realize that polyiso under a slab, below grade is a no no. Curious any comments on using it above grade on this application. I will be doing the double layer of plywood with a vapor barrier above the foam...

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |