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IdahoBob 08-27-2009 05:52 PM

Ants Destroying Ridgid Insulation
During a remodel a couple of years ago, I installed rigid poly-iso (the yellow stuff) insulation board over the tops of the exterior walls because there was no room to install R-38 batts and allow a air space above the insulation. Recently, I started to notice fine yellow dust on the deck below the soffits.

Upon removing a soffit panel, I found an infestation of common black house ants (not carpenter ants). The little buggers had been tunneling away in the insulation board and setting up housekeeping there.

I removed the insulation board and sprayed with pesticide. Now I need suggestions of what replace the poly-iso with. I have seen references to borate treated insulation board but have not been able to find a source for it.

Has anyone had this problem and found a solution?

flyboy 10-05-2009 11:40 AM

I do not have a solution for you but I have had the same problem in the past. Bugs really seem to like polysio insulation.

I have been told that foil facing is a deterrent but I have no way to verify this. For what it is worth, I also have styrofoam insulation and have not seen as much evidence that the bugs go for it.

A professional that does spray foam may have some means to mix in borate when blowing foam. I do not think the commonly available insulation boards (i.e. what is available at H.D.) have any insecticide. I have never seen any product marketed as such.

Let me know if you find a solution.

IdahoBob 10-06-2009 09:52 PM

UPDATE on Ants and Rigid Insulation
It got worse before it got better.:furious: I found that not only had the little buggers (actually identified as Odorous House Ants - Tapinoma sessile) had not only attacked the Poly -iso but had burrowed into some expanded poly styrene (the white stuff) Funny thing is the white stuff, called R-Tech and manufactured by INSULFOAM ( is labeled as Insect Resistant" at least to Termites and Carpenter Ants. I guess my ants couldn't read the labels.

I agree that the foil facing may be a deterrent but, in this case, the edges were exposed and they entered that way leaving the foil completely intact. Perhaps wrapping the cut edges with foil tape might work.

In the end, I had to pull it all out of the soffits as well as some sandwiched between 2x window and door headers in a 2x6 wall.:censored: I then had an exterminator come in and spray everything and gas the attic. For the next week there were dead ants everywhere:thumbup: I don't think I am exaggerating when I say I swept up thousands of them everywhere inside and out. So far no more sightings and I am putting things back together but not using ANY foam insulation strictly fiberglass.

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