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Making exterior crawlspace foam more termite resistant

Harlan Bauer | Posted in Green Building Techniques on

I”m building a tiny house in southern Illinois, zone 4, mixed-humid. Dry-stacked CMU crawlspace outside dimensions ~18′ x 18′ with 2″ rigid foam for ~R-10. Since the interior & exterior of the block will be “plastered” with surface bonding cement (SBC), would the following work to inhibit termite entry:
1. Install the foam board with thinset mortar (1/2″ notch) including to the footings?
2. Cover the exterior of the foam with fiberglass mesh from the footing to the top course (bond-beam + rebar) and lapped over into the interior (ie, under the mud-sill) , and the whole thing “plastered” with SBC?

If I’m meticulous with my detailing–owner/builder–the SBC should block all potential termite entry points, no?

Footing drainage via Form-a-Drain; all back-fill with crushed stone to grade; block to extend ~2′ above grade.

Can this be made to work? Cost and time is no issue–ever having to remove infested foam board is!

Thank you!

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  1. GBA Editor
    Martin Holladay | | #1

    First of all, I'm not sure if thinset mortar is going to work as a foam adhesive. I would use foam-compatible adhesive dispensed from a cartridge.

    Concerning your exterior foam detail: remember, you have to satisfy your local building inspector (assuming that you live in a jurisdiction governed by building codes), not just people commenting on Green Building Advisor.

    I live north of the the termite line, so I'm not going to comment on whether your method is going to thwart termites -- but I wouldn't want to bet on your side of this question. Termites are tiny little critters, and all they need is a crack.

  2. 5C8rvfuWev | | #2

    In this area, Harlan, a termite barrier is code -- you didn't mention it, so this is just a heads up. If you're not familiar, it can be aluminum step flashing of a shape you might use at the head of a window, just larger so it laps clean over the top of (here) our foundation. Not sure how that would apply for you.

    Also, you might want to search out foam board that is borate treated.

    In this are, we also have to keep a 3" termite inspection strip open so you can visually see the buggers' mud tunnels if they do go up thataway.

    Fiinally, a non-building solution that seems to be very successful -- check out "Sentricon" (tm) Very few places that use it here seem to have an issue.

    Are you pre-treating the subsoil under your build? that helps a lot. And in the prevention category, be careful not to bury scraps of wood, sawdust, etc w/in 20-30 feet of the structure, and measure foundation plantings so they are a minimum of 3 feet from the house.

    good luck.

  3. Expert Member
    Armando Cobo | | #3

    There are few termite resistant EPS on the market. All foam boards outside the foundation should be protected against construction debris and abuse.
    One brand is AFM Technologies:, also there is an old but relevant study of it:
    Another foam made of glass is FoamGlas®:

  4. Harlan Bauer | | #4

    Thank you for all your responses! More data:
    1. I live in a rural wooded area where there ARE termites--I'm having a large area around the building site bull-dozed of stumps, branches be planted in pasture. The area directly around the house is going to have stone paths and patios over sand, sloped to drain surface water away from the building. White clover is the only thing that's to be planted anywhere near the house
    2. No permits, no codes, no inspectors--it's the middle of nowhere--having said that, I consider code to be bare minimum--I'm shooting for best practice!
    3. Sorry, I took a termite barrier to be a given, but since you bring it up, would it be worth my while to use copper and solder all the seams?
    4. With Sentricon and pre-treating the soil, are these things that can/should be only done by a professional? The nearest authorized Sentricon contractor is 53-miles away from me according to their web site.
    5. I should have been more specific about thinset--I'm planning on testing un-modified, modified and SBC and see if any will get the proper adhesion to the foam board. I'm shooting for full contact to the block substrate--think best practice for setting tile where there is near 100% adhesion to the substrate. I'm basically trying to fully encapsulate the foam board on all 6 sides.
    6. FoamGlas looks ideal but pricey.
    7. I'm not keen on the 3-in inspection strip on the exterior, might I be better off moving the foam to the inside? Pros? Cons?

    Thanks again for all your input!

  5. 5C8rvfuWev | | #5

    Hi Harlan,

    Termite barrier: the seams should be sealed of course. Absolutely. But I don't know what you'd gain by paying for copper.

    Sentricon: it's sold only to "licensed professionals." On the other hand, I'm sure there are other bait systems out there ... maybe you can ask a professional if other possibilities are as good. I dunno. Many local pest control guys like to freelance ... if you do a search, you may find someone who lives closer to you who'd be willing the treat (or provide you with the material).

    The inspection strip is code here. And it's a huge energy drain ... I wasn't clear: foundations here aren't insulated from outside; the foam board is installed interior and that's where the inspection strip is, at the very top of the wall. this is an area where the termites team with the kudzu and eat buildings whole ... a mild exaggeration.

    Perhaps you can check with the agriculture/pest experts at Champaign-Urbana or Carbondale and see what they recommend. They would know how much prevention is needed and what would be overkill.

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