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Community and Q&A

Hiding old foundation vents

KevinEJ | Posted in General Questions on

I’m insulating a crawl space with existing foundation vents (like the picture).

What are best practices to protect from UV exposure and hide the wall insulation visible through the old vents? Would 30# felt last if sandwiched on the interior between foundation and insulation?

If I decide to cover the exterior, plastic foundation covers come up on an image search, but I can’t find anything being sold online. They’re also a bit tacky, I think. Is there a more elegant foundation vent cover solution I’m overlooking?

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Replies

  1. GBA Editor
    Martin Holladay | | #1

    Kevin,
    The best approach is to fill the opening with bricks and mortar, followed by stucco (to resemble the foundation).

    Failing that, a wide variety of materials can be used, including pressure-treated plywood or plywood covered with colored galvanized flashing. Pressure-treated plywood can be painted.

  2. GBA Editor
    Martin Holladay | | #2

    Kevin,
    Q. "Is there a paint that could be applied on the backside of rigid foam (Thermax or XPS) to protect and disguise it where it will show through, leaving the old vents and exterior as is?"

    A. Not that I know of.

    Q. "Foundation is concrete stemwall (plywood formed), no stucco."

    A. I assumed as much. I recommended that the bricks and mortar be covered with stucco, and to choose a stucco product that is about the same color as your concrete foundation. But it sounds like you don't want to install bricks and mortar.

    Q. "To fix rigid foam to stemwalls, do the furring strips need to be pressure-treated?"

    A. No. For more information on this issue, see "How to Insulate a Basement Wall."

    Q. "What's required R-value for the crawl space rim joist area? Same as above grade walls (R21)? Or is the R15 used in the crawl sufficient?"

    A. Most building inspectors would probably be happy to see the same level of insulation as is installed on the crawl space walls, but upgrading to R-21 does no harm. For more information, see "Insulating Rim Joists."

  3. KevinEJ | | #3

    Thanks, Martin.
    1) Is there a paint that could be applied on the backside of rigid foam (Thermax or XPS) to protect and disguise it where it will show through, leaving the old vents and exterior as is?
    This seems easiest if a product exists, but impossible to ever re-coat. The felt sandwich is probably a fire hazard in my forested area. Foundation is concrete stemwall (plywood formed), no stucco.

    2) To fix rigid foam to stem walls, do the furring strips need to be pressure-treated? In zone 5b, with R15 I'm at ~3" of foam, so my screws will have to be pretty long.

    3) What's required R-value for the crawl space rim joist area? Same as above grade walls (R21)? Or is the R15 used in the crawl sufficient?

  4. KevinEJ | | #4

    Martin,
    I haven't ruled out bricks, mortar and stucco; just looking for the most affordable simple solution for the vent disguising/insulation protection.

    Thanks for the helpful articles, I've reread these several times. I'll look into plastic anchors for attaching rigid foam instead of furring strips.

    If I have trouble finding fasteners and go with adhesive, is there a foam adhesive available that will adhere xps/eps to polyiso? Thinking of layering xps/eps under a thinner Thermax sheet on the interior to save money.

    Edit: found THERMAX Recommended Adhesives:
    https://dow-styrofoam.custhelp.com/app/answers/detail/a_id/3329/

  5. Steve Knapp CZ 3A Georgia | | #5
  6. KevinEJ | | #6

    Steve,
    Thanks, I had found that one earlier today searching youtube. Seems a bit complex and sized for a CMU foundation where you're ripping the vents out first. I'm trying to avoid tearing my plastic vents out unless necessary, so really am just looking for a cosmetic cover. I'll probably end up using painted pressure treated plywood stuck on with some pl premium.

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