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

Under-slab insect treatment

hunter_w | Posted in General Questions on

Wondering what the green-building community’s advice is concerning insect control under a slab or crawl space.

I know it is common to treat the soil under the buildings, or at least it used to be.  I didn’t due to general environmental runoff concerns when I built my own house a few years ago (slab on grade).

We have a constant year-round ant problem, despite achieving 0.6 ACH50 air sealing.  It is as though they’ve all decided to get out of the rain by living under our slab.

I work in this field and want to know what I should be doing instead so that my clients aren’t subjected to this.

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. Expert Member


    The biggest problem is foam. I was at an ICF build last summer and watched a trail of carpenter ants each carrying a piece of foam exit the house and wander off into the bush. I couldn't help thinking about houses with foam not only under their slabs, but the load-bearing footings. I've had my own house infested and it wasn't pleasant. They did a lot of damage in hurry.

    The treatment doesn't have to cause concern. Products like Bora-care are fairly benign. New builds should either use treated foam (which unfortunately isn't available in all regions) or have the foam and framing treated before closing in the walls. Spraying the perimeter of existing houses like yours is probably something that needs doing annually.

    As the use of foam has become more ubiquitous there needs to be more discussion about the possible ramifications of using something so susceptible to insect damage. I don't think enough attention is being paid to it yet.

  2. hunter_w | | #2

    Malcom, thanks for the reply. Luckily not carpenter ants. Just the little sugar ants and a slightly bigger variety that don't eat the building, just constantly wander every inch of it looking for food. We use the Terro ant bait, which works for a little while, then they come back. Seems like they are getting immune to it. One batch has been feeding off the ant bait for some time and they keep coming.

    I'll look into Bora-care, etc. I was always just worried about the poison travelling into ground water or runoff and getting beyond into the larger world. Anyone know if this has been looked into anywhere?

    1. Expert Member
      MALCOLM TAYLOR | | #3


      My experience with small sugar ants is while harmless, they seem to be the hardest to get rid of.

      Lots of insecticides leave residues and can contaminate the larger environment, but borate-based ones appear by most accounts to be pretty benign.

      1. hunter_w | | #6

        Appreciate it Malcolm

  3. Expert Member
    Peter Engle | | #4

    The Terro style liquid baits generally also use borate based chemicals, but of course the amount applied is tiny - only the amount the ants consume. unfortunately, they need to consume a lot of bait in order to take out a large colony. The recommendation from the baiting companies to frequently replace the baits and use several of them is probably the best way to go.

    Despite my general aversion to broadcast use of chemicals, I am a big fan of borate treatments and pre-treatments to foam and framing. So long as they are protected from flowing water, the chemicals should stay put for the life of the building. That they provide both insect and mold protection is a bonus.

    So far, no magic bullet for the ants, though. We've got them too, ever since we added exterior foam in a renovation. The baits knock them down, but nothing seems to work forever. This is certainly an area ripe for some grad students to research....

    1. hunter_w | | #5

      Thanks Peter

  4. Peter Yost | | #7

    Check out this GBA blog and whatever Mike Potter may have written recently as part of his university extension work at Kentucky:


Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |