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Community and Q&A

Termite and insect infestations using external rigid foam at the foundation

Ralph Hertlein | Posted in GBA Pro Help on

I am planning on a home in the Cleveland TN area and want to reduce “conditioning costs” to a minimum (<$50/Mo for all but water). I want to use cc slabs (4 – 6″) on the exterior of the foundation (full hight) but have been personally plagued by termite and carpenter ants in every home I have lived in. Short of soaking everything in dieldrin (hard to come by these days but worked beautifully in MO and has some nasty side effects), what is the current recommendation for stopping the critters outside the foam/concrete interface. I have seen that this is still a problem for ICFs (with manfs offering treated ICFs) so I am presuming that this is something that is still in the exploratory phase of development and we would like o start construction this Spring yet… What is the current thoughts please??? Thanks Much, Ralph

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  1. GBA Editor
    Martin Holladay | | #1

    If you are concerned about termites or insects in rigid foam, the first step is to check with your local building department to find out what the local code requires. In many areas of the country, you can't install rigid foam on the outside of your foundation.

    Regardless of your local code, here's my recommendation: if you are worried about termites, install the rigid foam on the interior of your foundation wall (whether you are building a crawl space or a basement). Leave a strip of your foundation wall uninsulated at the top of the wall as an inspection strip; that's where you will look for signs of termite activity.

    The bare, uninsulated portion of your foundation wall will leak heat. This is unfortunate, but it's the price you pay to live in a climate that is warm enough for termites.

    Finally, borate-treated EPS may provide some protection against insects. The best-known brand of borate-treated EPS is Perform Guard. Other manufacturers offer similar products; one is the Poly Molding Corporation.

  2. Lucy Foxworth | | #2


    What if you keep the foam dry by covering it with a layer of EPDM? Would that decrease the risk of termites? How about making a clay cap on top of the foam with bentonite clay, for example? Or perhaps a cementitious covering.

    Thank you. Lucy

  3. GBA Editor
    Martin Holladay | | #3

    Neither of your suggested approaches sound promising to me, but I don't live in termite country.

    If the foam is below grade, "covering" it with EPDM is irrelevant. If it's buried, it will be in close proximity to moisture.

  4. Jin Kazama | | #4

    For personaly knowledge, what is considered to be "termite territory " ??

    They seem to be a plague in USA from all i read ..we don't have any up here in quebec,
    but where does it start to be a problem ??

    We do have very agressive ( short season ) carpenter ants, and even though i was told a few times that they do not like EPS, i can tell you that they do venture within eps and in between joints ...
    But they will only do it if there is a smell on the other side! ( damp wood )

  5. GBA Editor
    Martin Holladay | | #5

    Right now, the termite line is somewhere near the Massachusetts/Vermont border. But I fear that the termite line may be creeping northward...

  6. Expert Member
    Dana Dorsett | | #6

    Backfilling the exterior with clean compacted sand of the right granular size can mitigate termite intrusions fairly well when surrounded by stable soils that won't settle or frost-heave creating gaps in the sand. Using copper flashing as the capillary break and termite shield for the foundation sill at the top of an ICF wall is another measure worth taking. The copper flashing is also a thermal bridge true, but worth it in high-risk areas. (As I understand it, like borates, copper compounds are toxic to the gut flora of wood boring insects, protozoans required for the host insect to digest wood.)

    Carpenter ants/ wasps / carpenter bees are almost always a sign that moisture is getting into the wood and unable to dry quickly. I'm not sure if the same is true for termites (it might be similar, or not.) Errors in flashing, undetected roof-damage/leaks etc are often at least partly to blame.

  7. Milan Jurich | | #7

    Would EPS type IX with the borate-treatment be recommended over XPS rigid? You give up little R-value in return for rigid that has a better chance against termites. Is there a anti-termite XPS product available?

  8. Ralph Hertlein | | #8


    Don't like your response but that is what I expected (nothing personal mind you)

    I have fought the little creatures in MO, GA and now expect them in TN. I have had them destroy a wall inside a garage that was treated by drilling the perimeter of the garage slab. They tunneled on the underside of the slab to reach the perimeter wall 8' inside the garage. Have also had them penetrate a 10" foundation wall through a stress crack below a treated section outside a foundation. They are persistent if the are anything.... Nature creates some great life forms...

    I do suppose then that the only real way to slow them is to assure that any wood close to a concrete wall or floor is to assure that the moisture content is below some threshold - would you have any idea on that? <19% or <10% or???? I am guessing that the wood/moisture combo is the attractant?

    Short of not using wood for construction - with the laws on the books today, is there anything that I could treat the dirt with to slow them a bit?


    Thanks to everyone for your comments/input. Natures recycling is too efficient if you ask me...

  9. John Klingel | | #9

    Have you talked w/ a local bug killer? Synthetic pryrethroids are deadly on ants, and may work w/ termites, too. The ants carry the stuff back to the nest with them instead of dying quickly, as apparently happens to them w/ borates. A pro bug killer friend of mine told me about the pyrethroids. One treatment was wicked on our carpenter ant invasion. I'd call one in your area(a bug killer, not a termite).

  10. Expert Member
    Dana Dorsett | | #10

    You don't need high density Type-IX EPS to insulate residential slabs or foundation walls- even Type-I is sufficient from a structural point of view under a 4" slab though Type-II is often the minimum density allowed by code. There are borate-loaded versions commercially available for ant & termite control.

    The moisture content of the wood has to be fairly high to make it attractive to most carpenter ants or wasps/bees, and if the moisture content is kept under 15% infestations of wood boring ants is all but unheard of. I'm not sure if that's always the case with termites- some termite species may tolerate wood that dry, but lower moisture is always better.

    Larger roof overhangs to limit direct wetting of siding/windows and correctly lapped wide flashing on doors & windows helps. Keeping plumbing & drains out of exterior walls where minor leaks might go undetected is also good practice.

    In new construction building with at least 6" of compacted stone under slabs & footings as a capillary break, and using EPDM or metal capillary breaks between the footing and walls in an ICF keeps the concrete from constantly wicking ground moisture up. (Capillary draw is powerful, and can pull moisture up several 10s of vertical feet if the footing is always wet and the wall coverings are somewhat vapor retardent.)

    In wood framed building in TN using building stackups that don't need interior side vapor retarders keeps summertime buildup of moisture in wall cavities lower since the air-conditioning can extract most of it. Insulating stud cavites with "sulfate free" cellulose that uses only borates as fire retardent also keeps the structural wood drier by buffering much of the moisture in the insulation. The borate fire retardents have similar anti-ant/ant-termite gut-flora toxicity. While termites are unlikely to move through the insulation (preferring to bore through wood, which is their lunch, unlike ants who don't need to eat wood, using primarily as a fortified nest), it will mitigate direct against ants and wood boring bees/wasps, and indirectly against termites by lowering the moisture content of the wood. There are cellulose formulations with higher borate content designed specifically for ant control out there too, but if you keep the wood dry standard borate-only goods would suffice.

    Masonry & stucco siding raises the moisture content of wood sheathing, making it more prone to insect attack. Using wood or fiber cement siding back-ventilated using mesh-type rainscreen materials keeps the sheathing drier and limits the traffic pathways into wood. (The Obdyke "Rainslicker" products are dead-easy to install under most types of siding. The 6mm or 1/4" goods are good enough for most applications, but if you don't have big roof overhangs the 10mm or 3/8" stuff is better.)

  11. Expert Member
    Malcolm Taylor | | #11

    Dana, I don't know where the correlation between Carpenter Ants and moisture came from but it isn't correct. They will nest in dry foam and bore through seasoned framing lumber that is well below 15%. Any material, such as foam, that mimics the dry, decaying stumps they prefer to nest in is susceptible to damage. I have seen severe infestations in south facing walls in the middle of summer where the framing and foam were warm to the touch. Untreated foam, especially now that builders have begun using it in situations where it forms part of the load-bearing structure can have very serious consequences.

  12. Lucy Foxworth | | #12


    I don't think anyone has talked much about stone material as a termite barrier. The types I researched online are made from rock and ground to a size that is too big for the termites to move, with spaces between that are too small for the termites and too hard to chew.

    In Australia this termite barrier is called BTB - basaltic termite barrier and in Hawaii, it's called GranitGard.

    I doubt it is easy to find in Tennesee though.


  13. Expert Member
    Dana Dorsett | | #13

    Malcom- ants may sometimes bore through dry wood, but they won't nest in anything but damp wood over 15% moisture content, wood that has more often than not been attacked by fungus. I was calling it out from memory, but looked it up due to your prompting- there are plenty of internet sources on the particulars, including sources citing 15% as a typical threshold. (eg: )

    Of course you can't believe everything you read on the internet, eh? :-)

    Some species of ant's seem to favor picking apart EPS beads (I've observed this with picnic-coolers), not just carpenter ants, but I'm not quite sure what that's about. (EPS beads as faux ant eggs, maybe?) I've seen EPS well-tunneled & traveled, completely riddled by carpenter ants, but never seen an actual nest in EPS- only found the queens & quantities of egg in wood. I'd be curious to see evidence that they actually nest in EPS if you can find an online reference(?).

    One of the guy in my office lives in an EPS core stress-skin post & beam house from the late 1980s, and while it's clear they use the EPS for tunneling in a superhighway system, the nests are always found in the structural timbers. (IMHO it's not a particularly well-built house from a flashing and moisture rejection POV, with plenty of issues undercutting it's thermal and moisture performance.) If they're in fact capable of nesting in EPS it might affect his ant-abatement strategy. DO TELL!

    Lucy- compacted sands of the right granular size are reportedly sometimes successful in the US (thought I'd mentioned it), but as you point out, whether finding local expertise on those methods may be tough.

  14. Expert Member
    Malcolm Taylor | | #14

    Dana, I wonder if there re regional differences in carpenter ant behaviour? Here in the PNW rainforest they are ubiquitous, but most active in the hottest part of the summer when they swarm and send out winged scouts to start new colonies. I often find their nests in the foam sheets insulating T and G ceilings which are somewhere between warm and hot with no moisture present. Perhaps at some point in the year there was a higher level to attract them to the location in the first place, but they sure don't move if things are dry during the majority of their tenure. To expand their nests I have seen them completely remove the double top plates between two studs, which at the time must have been under 6%. My experience has been the opposite of yours - that they will tunnel through sound wood but usually nest in the foam. I wish they wouldn't. They do so much damage before you detect them and it is almost invariable in a location where access in a problem. Thank God we don't have termites up here!

    Edit: All the nests I've found have been in Styrofoam SM.

  15. Jin Kazama | | #15

    I've seen alot of XPS horror pictures in google doing a simple search in images using " carpenter ants styrofoam " ... scary

    Can't seem to find any within EPS though, but i can confirm that they like to dig in it!!

    What about "peel stick" membrane covering the exterior insulation down to the footing ??
    Doesn't it keep the termites/ants away ??
    I don't see why i would install any insulation without some kind of membrane on it below grade,
    but it seems that some still do it from pictures...

  16. Expert Member
    Dana Dorsett | | #16

    Most visible ant activity will be during the warmer temperatures in any climate (they're cold-blooded critters after all) The moisture resident in roofing EPS under a not-so-permeable felt/shingle layup may make it a nicer place for them to hang out(?), but while I've seen ant-tunnels in roofing foam (both EPS and iso) in New England, the actual nests involved punky roof decking.

    Thanks for making the point- this discussion has prompted further conversation with my co-worker with the ant-riddled stresskin house, and is likely to adjust his detection & remediation strategies.

    So far I haven't had to deal with termites in my area, but they're close enough to hear them munching...:-) When I lived in the pacific northwest (western WA) I only encountered them a couple of times, but one was a house-condemning structural disaster. (They had to demolish the house and start over- donating the termite riddle wreck for local fire-department practice. :-( I wasn't there for the re-build.) I'll take carpenter ants over termites ANY day, but mayhaps I should be careful what I ask for!?

  17. Expert Member
    Malcolm Taylor | | #17

    Dana, My bemusement at finding carpenter ants in the roofs of projects I was renovating turned into something a bit more personal when they infested the band of SM that runs around my own house at the second floor rim joists. The colony moved on after each of my attacks to destroy another section of foam before I finally got rid of them. The whole West Coast laid back vibe disappears pretty quickly when you hear hundreds of little jaws crunching in your walls!

  18. Jin Kazama | | #18

    Malcolm: please explain " SM "

    Why were the ants trying to nest in there ?? any wet wood was found at this place ??

    What is normally used as a wall climbing barrier for ants/termite ?
    i've never seen anything used here in Quebec, but i recall reading about insect flashing method
    or something around here ..??

  19. Expert Member
    Malcolm Taylor | | #19

    Sorry Jin, I abbreviated the full name down from "Styrofoam SM". The ants are everywhere here and will nest where ever they find suitable material - in this case foam. Like rodents they also seem to appreciate a heat source and are often found in walls directly behind electric baseboard heaters. Unlike termites they don't have a food source in the house so you can usually spot their foraging trails going to and from their nest. I suspect it would be very hard to flash or seal the exterior tightly enough to stop them getting into a house. On one project I worked on, after the pest control had surrounded the building perimeter with insecticides, the ants found another route out along the telephone cable and down the pole at the road.

  20. Jin Kazama | | #20

    Wow your carp ants are agressive!!
    I didn't cut much trees on my land around my house,
    so i have alot of ants because of the forest still intact
    i sprayed some nasty stuff my father gave me the first 2 years ..which is illegal now i believe here.
    But i got some ants trying to get in every summer since then.

    I'll try and find the flashing product i've seen in the past when i get some time.

    What about peel and stick ?? do ants and termites eat through that or not ?
    if we can at least make sure they don't go up the wall and or inside the exterior basement insulation, gives us a better chance.

    This problem will need to be adressed if exterior foam insulation is going to be the norm in the coming years...nobody wants their investment ruined by insects, and the fact that they tunnel/nest in the insulation removes the "durability" advantage of many insulation boards.

  21. Stephen Martinson | | #21

    Have you thought of using mineral wool boards instead of foam for the foundation walls?

  22. Hein Bloed | | #22

    Here a report in a German newspaper about ordinary garden ants nesting in a PH EPS foundation.,15189134,20943954.html

    The house wasn't 2 years old and consequently demolished. Watch the video.
    These wheren't termites or carpenter ants, just the ordinary common black garden ants.

    There is only 1 method to protect underground EPS foam against insects: fine stainless steel mesh. This is wrapped around the EPS and should last for generations. Used in France, Switzerland and other places.

    The alternative to plastic foam would be foamed glass.

  23. Jin Kazama | | #23

    Hein: why demolish the hole house ?? ///2 years old Passivhaus ?? geee
    hope the insurance covered that !

    Can you link the SS mesh product??
    interesting idea to use a mesh ... are ants a big problem in deuthscland and around?
    Down to what depth is the mesh installed ?

    is it ok to use mineral woold boards undeground ?

  24. Ronnie Allen | | #24

    I have personally seen ants bore through a EPDM roof. I wouldn't depend on it or any roofing membrane as stop for insects.

    We had a persistent leak on a hospital in Baton Rouge. Ballasted EPDM 0.060, I swept the rock back over a large roof area to inspect for myself. As the EPDM was drying in the sun, I noticed a bunch of small spots on the EPDM that remained wet. (Giveaway for the leak spots). Each was a small hole. I cut back the EPDM to find ants everywhere within a soaking wet EPS insulation. I don't think the ants eat the EPDM, but they certainly weren't allowing the membrane to stop them in the pursuit of where they were going.

    This isn't a common problem for roofs but it does happen and it is something I now look out for.

  25. Hein Bloed | | #25

    @ Jin Kazama:

    The house was demolished after the terminator used overdoses od pesticide to kill the ants, the people in the house got sick.
    During demolishion the demolishen team lifted the base plate and got to the EPS infested with ants, still alive.
    Here it became clear that they had tunneled quite a lot and the house would have become instable anyhow, like building on drifting sand.

    The latest I've heard about the case that the terminator doesn't want to pay for the demolishion, blaming the structure was already instable anyhow.

  26. Hein Bloed | | #26

    To protect a plastic foam against insects the stainless steel mesh as used for windows and doors can be used.
    It is wrapped around the entire insulation.
    Laid out on the hard core, the EPS placed down and then the mesh being folded up and over the sides. Like wrapping a parcel.

    Foams have the disatvantage that they contain air. Animals gnawing the foam do not have to dispose the remnits outwards, as a soil-tunnel digging rabbit would do for example.
    The shredded foam offers enough space (the air) to simply store the gnawn EPS particles within the tunnels.
    So no or very little traces of tunneling activities can be found outside.
    Secret miners - so to say.

  27. Hein Bloed | | #27

    Ronnie Allen wrote:

    "I cut back the EPDM to find ants everywhere within a soaking wet EPS insulation."

    You have to tell this the DIYers, they don't believe in EPS becoming soaking wet - even in underground installations........
    It's my experience as well, the stuff takes up water over time. And loses therefore a good deal of it's thermally insulating properties.

  28. Jin Kazama | | #28

    Wow you guys are all scaring me .. i hate those carpenter ants !!! and my personal house is EPS/ICF :p

    Ronnie Allen : are you sure that ants can dig EPDM ?? maybe the holes were there before and they only used it ?
    how small were the holes? cause i don't see a ant going through a closing slit of epdm easily ...

  29. Hein Bloed | | #29

    EPS-recycling by the blue ants (wink-wink)

  30. Ronnie Allen | | #30

    @ JIn - I am positive it was from the ants. I am not saying though that the ants were attracted to the EPDM or the EPS. I know of another roof the company I worked for was having an issue with them as well. The holes were very small, but large enough to allow water through to leave the small wet spots as the EPDM the rest of the EPDM was drying.

    @ Hein - I would say they could ask any commercial roofer. EPS and Polyiso both becomes completely saturated with water if they under a leaking roof. They can become so heavy with water, that they crumble when you try to pick them up.

  31. Jin Kazama | | #31

    OK OK RONNIE ! i get it!! ( refferring to the triple post :p )

    I seriously don't understand how a ant can dig in a such resilient matter that is EPDM rubber membrane .... incredible! but at the same time ..very scary !

    Were the ants attracted by some wet wood under all of that ?

    I can't believe they dig in the EPDM because they wanted to make a nest there...

  32. Jin Kazama | | #32

    So what exactly is considered to be the correct metal flashing for near ground vertical walls to prevent ants to climb the walls ??

  33. Ronnie Allen | | #33

    Sorry about the triple post, I didn't do that. I am not sure about the cause of the ants. I got the hospital maintenance guys I was working with to check out what I found. They got some extermination work done and I sent a service crew out to replace the area. I also believe the ants entered the roof some other way and bored out, but not sure.

    You could always call an EPDM manufacturer, (Firestone, Carlisle), and get their input as well.

  34. Jin Kazama | | #34

    Ronnie : i will call Firestone, been using their products alot, and i will be using them in the future
    and this probem concerns me because carp ants are everywhere around here...

  35. Jin Kazama | | #35

    Ronnie: my FBP rep asks me if we can provide him with a picture, would it be possible ????

    If not, could you please give me a quick resume of the situation where u saw ants dig through the membrane ?? he would discuss with hq and see if they received feedback about this etc...

    In an way, i am interested in knowing more about this issue as carp ants are present locally, and i intend to use EPD over insulation in the next years ...

  36. Tony Fleming | | #36


    We recently addressed this question when we did a deep energy retrofit that included wrapping the house in thick rigid foam and applying FP-ultralite foam panels to the exterior of the concrete foundation. We live in NE Indiana…land of many lakes, wetlands, and subterranean termites. Our house was built in 1890 and a couple of places showed signs of having had termites decades ago. We worked with a pest control company to identify the most likely pathways for termite infestation and design our solution.

    The key location to protect is the hidden surface between the foam and the concrete. We ended up designing a 2-part flashing system that literally would force any termites that might tunnel up behind the foam out to the surface. The key element is a J-flashing that wraps around the top of the foundation foam panel at about the sill elevation. The long leg of the “J” is adhered to the concrete with a continuous double bead of silicon adhesive (the pest control operator said that termites will not go through silicon), while the short leg extends back down the front of the foam panel. Any termite tunnels in the foam or on the foam-concrete interface are literally redirected
    back to the outside where they are visible.

    A second modified “Z” flashing rests directly on top of the J flashing and wraps around the rigid foam that is applied to the house sheathing. One leg (~6” high) is adhered to the sheathing with the same silicon adhesive (also stapled to hold in place while the adhesive cured), the second leg passes under the foam (and directly on top of the Z flashing below, sealed with more adhesive), and the third leg bends vertically downward over the top of the J flashing. The Z flashing mainly protects the bottom of the polyiso and helps drain any bulk moisture that might get into the wall assembly outward, but it also serves as an extra termite barrier.

    This process sounds like a lot of work but it was actually rather easy and took about a day to make and install. Our flashing consists of standard white aluminum flashing and was bent on site using a regular metal brake (you could also have this done inexpensively at any machine shop). The photo shows the installed flashing before any foam panels were applied.

    Your first step is to identify which species of termite(s) you are at risk from. Subterranean termites are the most common in temperate latitudes, but other species, such as Formosan termites, come into play in the south and near south. Different species have different requirements viz moisture, light/darkness, wood, etc. Beyond that, excellent drainage away from the foundation is essential for any system of insect protection. Note also that subterranean termites need moderate soil moisture to get to the foundation, but once they construct their tunnels on your foundation, the moisture content of your home’s components is irrelevant.

    Hope that helps.

  37. Derek Roff | | #37

    Regarding stainless steel mesh to protect buried foam from insects: Stainless steel is highly corrosion resistant when it has sufficient, continuously renewed contact with oxygen to form the protective oxide layer. Oxygenated water is fine, but stainless steel bolts can corrode in damp or immersed situations, where there is no air or water exchange. I'm not sure fine stainless steel mesh can be counted on to remain intact, in a damp, buried situation, such as under a building slab or foundation.

  38. Expert Member
    Malcolm Taylor | | #38

    Derek, that is a real concern. With something as small as ants I don't see how any on site protection of foam could be effective. The only viable solutions I can imagine are either encapsulation at the manufacturing stage by some sort of coating or incorporation of insecticides again during manufacture.

  39. Jin Kazama | | #39

    Do carp ants dig in Polyiso ? i have not found a single picture on google showing ants in poly boards...

  40. Hein Bloed | | #40

    Regarding stainless steel mesh:

    There are different types of stainless steel.
    Read the label.

  41. Ralph Hertlein | | #41


    Thanks much for the details and I think I can understand (I am a visual guy and need the picture or cross section... can't seem to find so if you can send directly - appreciated).

    It sounds as if you have had much fun trying to stop insects.

    I am now experienced multiple times over and am approaching the view that Mother Nature wins every time - just how much is the only question.

    Also the crushed granite seems to be a better solution as the only way to fight Mother Nature is to use her "ways." I will look into that as I hate leaving the thermal mass on the outside. I have designed several passive solar addition elements and the mass means quite a lot in all seasons if done right to mitigate the internal temp swings.

    As far as the ants - they are worrisome to say the least but the key to all of this (from my view) is to control the moisture flow mechanically even if it takes a bit more time) so that the food chain is reasonably controlled.

    That is my other concern - in a super insulted double wall - do I seal it totally and hope for the best or do I calculate to create a dual breathing envelope in the hopes the climate in TN does not alter too much over the next 30-40 years...?

    Again - thanks to everyone for all the great insights!!

    Nothing replaces the combination of knowledge AND experience


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