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Is foamboard and stucco to the ground in a pier and beam house a termite risk?

michaelbluejay | Posted in Green Building Techniques on

SUMMARY: I’m contemplating installing foamboard + stucco over existing wood siding, running it all the way to the ground on my pier & beam house, but worry whether this could invite termites.

DETAILS: I want to insulate & encapsulate the area under my pier & beam house, but there’s not enough space under the house to work, and the existing stucco walls aren’t smooth for attaching foamboard even if I could get under there. At the same time, the exterior paint is peeling and likely contains lead, and repainting every X years is expensive and wastes paint if there’s an alternative. So, my idea is to annihilate two birds with one rock and to install foamboard and stucco like so:

(1) Demo the existing, damaged stucco skirting
(2) Install 1/2″ polyiso over the existing lap wood siding, but not over the old skirt area.
(3) Install 2″ XPS at the old skirt area, set in a channel dug 2″ into the ground, with its outside face being in a place with the 1/2″ polyiso on the walls.
(4) Air-seal the top of the polyiso with canned spray foam, and all other seams with housewrap tape.
(5) Install 1×3″ vertical fir strips to the foamboard, but ending 8″ above the ground, so ground-based termites can’t easily sense the wood.
(6) Install metal lathe and stucco.

However, I remember reading that running foamboard to the ground can invite termites somehow. I’m in Austin, TX, climate zone 2, which is a bit humid, but my reading of the local code is that there’s no ban on foamboard to the ground. I installed gutters and am putting in a French drain on the high side of the house to try to keep the soil around the house as dry as possible.

Is my plan sound, or does it suffer from inviting termites, or maybe some other problem?

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  1. GBA Editor
    Martin Holladay | | #1

    The termite threat varies widely from location to location, so you should seek local advice. That said, if termites are a problem in your area, you should probably avoid extending rigid foam all the way to the ground.

    For more information on skirts, see this article: Crawl Spaces vs. Skirts.

  2. michaelbluejay | | #2

    Okay, I'll consult with local pros.

    One thing I'm wondering, though: is the risk that termites are somehow more likely to crawl up the foamboard than the existing stucco skirting? For that matter, they could have crawled up the concrete piers which are only 3" below the house's wood frame on the low side of the house. (I'm currently excavating it to increase that distance.) I'm not understanding what it is about foamboard that makes it a greater risk for termite mountaineering than any other material that links the ground to the house.

  3. Expert Member


    Termites like to tunnel and live in decaying wood. Materials, like foam, that mimic that wood are more susceptible than others.

  4. JC72 | | #4


    Termites need moisture to survive so they build mud tubes when forced into the open air. If you see these little tubes on the piers you'll know that you have/had activity in the area. Of course you can pay a pest control company to treat the surrounding soil and perhaps add some sort of sand (4-inch thick, 20-inch wide layer to be effective) boundary around the outer edge of the house.

  5. michaelbluejay | | #5

    @John, I'd love to add a sand barrier, but according to Texas A&M, 16-grit sand (the only kind shown to work) isn't available commercially in Texas, and I certainly couldn't find a source in my search. But that got me thinking, maybe other materials thwart termites. I found a journal article that showed that termites can build out of damn near anything, including glass beads and bits of copper:

    But while they could build out of salt, they had a real tough time of it. Sam's sells 25 lb. bags of salt for $4.98. (Agricultural feed stores have cheaper salt but it contains things other than salt.) For a 4" deep x 20" wide trench, around an 80-ft. perimeter, I'd need 44.4 cubic feet or $1228 worth, so that's a non-starter. Landscape glass is about half that but still kind of pricey.

    So, maybe pebbles? Too big for termites to build anything out of. I could put landscape fabric under it so they couldn't easily import dirt from under the pebble layer. I might need to go deeper than 4" to keep air from flowing through the pebble layer, ruining my goal of sealing up the skirt. If only 4" deep, pebbles would run around $400 from Home Depot by the bag, less from a landscape supply house.

    Heck, why not just concrete? Let's see them build out of *that*. That would be only around $300, too.

    @Malcolm, if termites are attracted to foamboard because it mimics wood, then it seems I could easily thwart them by gluing aluminum foil to the XPS with foamboard adhesive (DIY foil-faced), and taping the seams and edges with metal tape. I could sink it into the concrete. I'll run that by the local expert.

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