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

Fastening details – deck ledger to insulated slab

user-5293988 | Posted in Green Building Techniques on

I am designing an insulated Monolithic Slab. I plan to install 4″ of Roxul comfort board beneath and around the perimeter of the slab.

Does anyone have experience attaching a deck ledger to a slab (or stem wall) that is insulated with Roxul? Or is it advisable to place a higher density product beneath the ledger to avoid compression which may happen with the Roxul Comfortboard?

What type of fasteners are recommended for this application? Would a standard wedge type concrete fastener like a red head work?

Other solutions?

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. GBA Editor
    Martin Holladay | | #1

    Michael,
    First of all, it's hard to imagine a situation where a deck ledger would be attached to the perimeter of a slab. It sounds like the deck would end up too close to grade.

    That said, your best solution is to support the deck on independent footings.

  2. user-5293988 | | #2

    Martin,

    My plan is to leave the top of the grade beam & slab at 10" above grade. This will give me room to have a 2x6 ledger.

    I am trying to stay away from Independent footings for two main reasons:

    1 - interfering with horizontal roxul insulation as per fpsf guidelines
    2 - detailing the water barrier atop the insulation sounds hairy (to ensure water drains toward the perimeter drain at the outer edge of this horizontal insulation)

    From what I observe, an attached deck or porch is a fairly common feature to many buildings and is a great way to blend inside/outside space.

  3. Expert Member
    MALCOLM TAYLOR | | #3

    Michael,
    If you want to connect the ledger through exterior insulation I'd suggest offset supports such as Maine Deck Brackets. One caveat is that they are made of aluminium so you would need to provide some barrier (a piece of membrane?) between them and the concrete, and select the anchor material carefully.

    When a deck is going to be that close to grade, I either make it a patio, or if wood is the preferred finish I construct the deck on a bed of gravel with no ledger, beams or posts, so that the whole deck is load bearing.

  4. user-5293988 | | #4

    Malcolm,

    Thanks for the tip about the deck brackets - that solution shows potential. I like the idea of keeping the framing and decking spaced away from the building to facilitate drying.

  5. Expert Member
    MALCOLM TAYLOR | | #5

    Michael,
    There are a few variations on the same idea. The Remote System uses blocks of PT wood.
    http://www.cchrc.org/docs/best_practices/REMOTE_Manual.pdf

    Good luck with your build!

  6. user-5293988 | | #6

    Thanks for the link Malcolm.

    There are many great photos and diagrams for attaching ledgers through thick foam to a building to a rim or band joist.

    Recently I came across this diagram of using anchor bolts to attach a ledger with an icf system..although the diagram doesn't have any insulation between the framing and the concrete. Maybe I could use the embedded anchor bolts and pass them through either some pt blocks (as in the remote system) or some high compression XPS or CompacFoam before going through the ledger.

  7. Expert Member
    MALCOLM TAYLOR | | #7

    Michael,
    Either might work. The only solution that will probably be accepted without an engineers stamp is the Maine Bracket. All the rest are going to need some professional input at some point, so it's a bit of a guess what they will be comfortable specifying.

  8. EthanT | | #8

    I am very curious about Michael Iacona's CompacFoam ledger detail mentioned above. Is there any way to save it from the error code currently displayed?

  9. GBA Editor
    Martin Holladay | | #9

    Ethan,
    I tried, but I can resurrect the image. It seems to have "illegal characters" (spaces) in its title.

Log in or create an account to post an answer.

Community

Recent Questions and Replies

  • |
  • |
  • |
  • |