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Vertical foam on inside of basement walls - termite pathway?

Last Post 23 Aug 2010 08:45 PM by Houseinthewoods. 8 Replies.

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Houseinthewoods User is Offline

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Posts:17

21 Aug 2010 05:43 PM
We just looked at a spec house that is supposed to be Energy Star + certified. The basement walls are poured concrete, and the basement has a walk-out on one side. We're located in Missouri, just south of Kansas City. The builder used 2 inch XPS on the inside of the poured walls, from the top of the basement slab down 24 inches. The bare foam is visible around the edge of the floor slab. While I appreciate the use of perimeter insulation, I'd worry about termites burrowing through the foam to reach the framing. This foam is going to be completely covered with finish materials. Is this a valid concern? The builder said it wasn't a problem (of course...)

Alton

Veteran Member

Posts:2164

21 Aug 2010 07:55 PM
If the foam has been treated with borate then I would not be too concerned. I think Missouri would be a good state to use Thermomass technology since the foam is protected by a wythe of concrete on each side.

Residential Designer & Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period . 334 826-3979

jonr

Senior Member

Posts:5341

21 Aug 2010 09:17 PM
I'd guess that the foam isn't treated. But I expect that there is some termite poison that could be applied to the top edge.

Alton

Veteran Member

Posts:2164

21 Aug 2010 10:29 PM
Spraying the foam with present day chemicals would work for awhile. Since we can no longer use Chlordane (Chlordan) to prevent termites, we really do not have long lasting poisons that I know about. Although borate is not considered a poison, termites can not tolerate it and can not build up a resistance to it like some current treatments. If one uses borate treated foam, then care must be taken that not too much is washed out by rain before it is covered. Years ago we used to sprinkle Roach Prufe (main ingredient is boric acid) on top of the bottom plate right before the fiberglass insulation was installed. This was primarily to prevent roach infestation but I understand it also offered some protection against termites. Paul Harvey used to advertise it to be used against roaches.

Residential Designer & Construction Technology Consultant -- E-mail: Alton at Auburn dot Edu Use email format with @ and period . 334 826-3979

Houseinthewoods User is Offline

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Posts:17

23 Aug 2010 03:03 PM
The builder used plain Dow Styrofoam blue board. Dow's documentation does not mention any kind of insect deterrent in this. Dow does have a product specifically for this application: STYROFOAM™ BLUEGUARD™ insulation is a termite-resistant extruded polystyrene foam insulation specifically designed for insulating foundations in areas with termite activity. STYROFOAM BLUEGUARD insulation contains the Preventol* HS100 insecticide, which protects the foam from termites and other wooddestroying insects. The insecticide is confined within the plastic of the foam matrix of STYROFOAM BLUEGUARD insulation during the manufacturing process, ensuring it will remain intact for the life of the insulation. This is not a surface treatment. It will not wash off or leach away. Preventol HS100 is deltamethrin. The app note says you should wear gloves and long-sleeve shirt when handling it. It sounds like this would be a great way to provide some termite protection for the life of the structure. I think I'd specify this if we decide to have this guy build us a house... Thanks!

Bob I

Veteran Member

Posts:1435

23 Aug 2010 05:32 PM
The foam is a thermal break so that the slab does not lose heat through it's connection with the foundation, so from that standpoint the builder is correct and building according to current building science. As to whether termites can get to it; do they /will they burrow deep enough so they can get under the foundation? Have termites been a problem by accessing a basement through cracks? (we haven't seen termites this far north yet, so I don't have experience with these guys). I've always been under the impression that they access houses via the foundation that is above grade - is this not the case?

Bob Irving<br>RH Irving Homebuilders<br>Certified Passive House Consultant

Dana1

Senior Member

Posts:6991

23 Aug 2010 06:25 PM
Posted By Bob I on 23 Aug 2010 05:32 PM The foam is a thermal break so that the slab does not lose heat through it's connection with the foundation, so from that standpoint the builder is correct and building according to current building science. As to whether termites can get to it; do they /will they burrow deep enough so they can get under the foundation? Have termites been a problem by accessing a basement through cracks? (we haven't seen termites this far north yet, so I don't have experience with these guys). I've always been under the impression that they access houses via the foundation that is above grade - is this not the case? I'm not sure how deep they'll go in your neighborhood but they can go pretty deep- even a few tens of feet. In the warmer parts of southern US they tend to colonize within 5-6 feet of grade, but many basement slabs are about that deep but they can & will dig deeper. Sand termite barriers are often specified to extend 8' below grade. (I have a neighbor in the extermination biz- when I get him going I get no end of extraneous data on wood eating insects. :-) )

Bob I

Veteran Member

Posts:1435

23 Aug 2010 08:15 PM
So how about sealing off that foam by gluing down a metal barrier over the foam?

Bob Irving<br>RH Irving Homebuilders<br>Certified Passive House Consultant

Houseinthewoods User is Offline

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Posts:17

23 Aug 2010 08:45 PM
Posted By Bob I on 23 Aug 2010 08:15 PM So how about sealing off that foam by gluing down a metal barrier over the foam? That seems like a good idea, but I think it's too late. We were in the house again yesterday, and the finish carpenters are done and the woodwork is painted. I'm sure they are planning on covering the bare foam with carpet. They will have to hold the tack strip back a ways from the baseboard, since the foam is exposed past the baseboard. This may not be a big deal, but it seems risky to me. The builders are a couple of young guys, and they are really trying to do the right thing from an energy point of view. Very few builders around here give a damn about energy efficiency.