GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Copper barrier for termites?

user-1119003523 | Posted in General Questions on

I’ve been considering the various ways I can address subterranean termite issues as I work on re-siding my house.

 Currently, the house sits on 6×6 sill beams, some of which have been rotted from weather exposure or damaged by termites. The house foundation wall extends consistently 30” above ground level.

 In addition to protecting the sill beam, I’m also using 2” of rigid foam under my siding and I want to make it especially hard for termites to get to.

 At this point, I plan on soaking the wood structure at least 12” above the foundation with Boracare.  At the bottom of the siding and foam, I’ll have a drip cap.  Rockwool insulation with a protective surface will cover the outer foundation wall below that.

I can apply an elastomeric coating / Drylok to the foundation and sill to protect it from water intrusion, but the only additional termite barrier I can think of would be copper flashing under the drip edge between the bottom of the siding and the top of the foundation wall insulation.

 But that poses a problem – how do I splice flashing, since I can’t wrap my entire foundation in a continuous strip? Given that termites need 1/64” of an inch to find their way through, it makes me question the value of copper flashing as a whole. I’d hate to have to try to solder the laps together…

i did read somewhere that butyl tape is especially effective, so maybe an asphalt membrane spanning the sill and at least the top of the foundation wall instead will do.

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. PLIERS | | #1

    This goes against everything GBA stands but I think insulating on the exterior with rigid foam is too risky in a termite zone. I would focus on insulating from the interior. Termites like rigid foam no matter what chemical warfare you use on it, they will find a way. If anything at the bare minimum keep rigid foam off anywhere near ground level.

    Of course i’m not an expert, but with proof termites were an existing problem I would be extremely cautious.

    1. Expert Member
      Michael Maines | | #4

      Many of us at GBA don't believe in using foam any more than absolutely necessary; the reasons include occupant and installer health and negative environmental impact. I would add the potential for insect infestation to the list.

      1. user-1119003523 | | #6

        What, exactly, is the risk to installers / occupants when rigid foam is applied to the exterior sheathing?

        Given that I’ve not seen evidence of them in 15 years with the regular abatement we do, I’m really not terribly worried about an infestation. This is just another layer of protection for it.

        1. Expert Member
          Michael Maines | | #7

          I meant in general. Breathing and eating foam dust is not good for you (or for other living things), foam is flammable to varying degrees, used improperly it can lead to mold, etc.. Rigid is safer than foam sprayed on site.

  2. user-1119003523 | | #2

    Rigid foam on the exterior is non negotiable, I’m afraid. I haven’t seen evidence of termites in 15 years, and so long as the perimeter abatement is maintained, I’m not really worried. The foam stops 30” above the ground at the top of the foundation wall, in any case..

    Really, I’m much more concerned about protecting the sill at this point, but a lack of a physical termite barrier for the sake of the foam does concern me.

  3. gusfhb | | #3

    Well, you can solder copper. One of those cartoon big soldering irons.

  4. Expert Member
    Michael Maines | | #5

    The main reason for "termite flashing" isn't to stop them but to force them to make mud tunnels to get around the projection, which can be easily seen upon inspection, and a cue to get a pest control professional on site. It doesn't have to be copper; any durable metal will work.

    I have had copper water table flashing fully soldered but it's a major project and expense, and with temperature-related expansion and contraction, it's not as simple as just overlapping and soldering the pieces. I don't know for sure but I doubt termites would get through an elastic sealant such as Big Stretch, so I'd be inclined to seal the overlap with something like that.

    As far as I know, Boracare only works when the insects chew the wood, so only treating the bottom 12" may not be enough.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |