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Community and Q&A

Ant Shield at Sill Plate

arnoldk | Posted in General Questions on


I live in Ottawa, Ontario where termites do not live (at least yet) but we do have carpenter ants. I know of a few custom homes which have installed something like this but 99% of the home in the area do nothing.

Is it worth installed some type of termite/carpenter ant shield at the sill plate or am I just over thinking things?

Thank you,

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  1. woobagoobaa | | #1

    We soaked the interior and exterior sill areas (to about 1 foot height) with BoraCare.

  2. Expert Member


    Wooga Gooba has it right. If you allow carpenter ants to set up colonies and forage near the house they will get in. I don't know of any effective shield. Treating the sill area and bottom of the wall cavities with borates is a good idea, as is leaving a clear area around your foundation so you can monitor their movements. They are primarily looking for things that mimic the rotten stumps they like to live in, so exposed foam is a real problem. They like damp conditions, but there is misapprehension that damp is necessary for them to colonize a house. They are quite happy with0ut it.

    1. Andrew_C | | #3

      This is a bit of a peripheral rant, but I just don't get people that landscape with mulch or bark chip around the outside of their house. Putting moist decaying organic matter next to the house is equivalent to rolling out the red carpet for bugs. As Malcolm says, leave a clear area around your foundation.

      1. woobagoobaa | | #11

        Agree re: clear the foundation of all organic matter. We will be putting a crushed stone moat 2' wide around the entire house and likely doing occasional Termidor treatment on the exposed foundation. About 1/3 of our 100 yr old sill had to be replaced due to water/bug issues. I don't plan on doing that again any time soon.

    2. arnoldk | | #4

      I have never heard of anyone having issue with carpenter ants in their house but I am also not in the industry so I reach is limited. I will check out the BoraCare product.

      As for foam, the City has requested we put an frost protection skirt around the house. I am really hoping the City inspector will allow us to use Comfortboard instead of EPS foam shown on the drawing. We worked so hard to avoid any exterior foam for this very reason.


      1. Expert Member
        MALCOLM TAYLOR | | #10


        Living in the rain forest here on Vancouver Island I've unfortunately had to deal with quite a few buildings with extensive damage from carpenter ants. Often in rotten wood, but also in foam, and I don't see a big correlation between foam moisture and infestations. They are perfectly happy to nest in dry foam on the south side of a house (including my own).

        I agree with Bill, a gravel barrier is good idea. On this house anywhere that didn't have a paved area adjacent to the foundation had a strip of gravel bordered by a PT 6"x6" (visible on the right hand side). The owner having had a bad experience in the last house he built. So far so good.

  3. Expert Member
    BILL WICHERS | | #5

    I've never seen carpenter ants nest in dry wood. I have seen them in moist wood. If you take care to detail your house properly so that you don't get water inside any of your framing, that will help. Boracare is good insurnace too. It's sometimes possible to build screening into areas at extreme critter risk. I've sometimes embeded hardware cloth into spray foam to keep out mice, for example. If you are worried about carpenter ants, you need finer mesh -- but stay away from aluminum screen since it will rot away in a short time. Fiberglass screen will last, but the ants can chew through it. Stainless steel screen is the best option, but also the most expensive.

    I second keeping a clear area next to the house. Some people use gravel for this. You can landscape, just make sure there is a good gap between plants and the structure. Make sure the soil isn't built up to wood parts of the home either -- keep some of the masonry foundation as a barrier.


    1. arnoldk | | #6

      Hi Bill,

      There will be about a foot between the lap siding the final grade and I'm considering putting either gravel or sand 8 inches around the perimeter of the foundation.

      Thank you,

      1. Expert Member
        BILL WICHERS | | #8

        Gravel will work better than sand as an insect barrier. Insects can tunnel in sand, but they can’t build anything in gravel. Something like washed pea gravel works pretty well.


        1. arnoldk | | #9

          Noted. Thank you Bill


  4. plumb_bob | | #7

    I recently was at a house where some form of insect (ants assumed but not confirmed) ate away huge amounts of the ICF external foam. The owner only found out when the basement started to flood as a result of the foundation drains being plugged with bits of foam. So...take bugs seriously.

  5. user-2310254 | | #12

    It's my understanding that carpenter ants are primarily nocturnal--although scouts are out all the time. Protecting the perimeter is fine, but it's important to watch out for shrub and tree limbs as the landscaping matures. Anything that touches the house can provide a convenient highway for carpenter arts.

    1. Expert Member
      MALCOLM TAYLOR | | #13


      Once we realized they had established a nest in our house, we surrounded the perimeter with a barrier of borate. They established a new foraging route using the cable from our roof to a satellite dish located on a pole in our yard. Individually they aren't much, but as a group I think they are smarter - or certainly more inventive - than me.

  6. user-2310254 | | #14


    I understand, having battled the critters at my first house. A pest control company recommended borate powder (for inside the walls) along with a perimeter bait the ants could carry back to the nest. This sorta worked, but it was an ongoing battle.

    1. woobagoobaa | | #15

      An on going battle ... so true!

    2. Expert Member
      MALCOLM TAYLOR | | #16


      At my own house, once they had concentrated their forage route on the satellite wire, I was able to leave liquid bait there which I assume they took back to their queen. After several days, following some signal they must have received, they all poured out of the wall at once onto our back patio and died en masse, leaving hundreds of corpses. It was like something out of a science fiction movie.

      1. Expert Member
        BILL WICHERS | | #17

        My guess is the "signal" was that their queen died. As I understand it, the survival of the hive is very, very dependent on the health of their queen. Ants are very devoted little guys!

        Note that the queens are very much larger than the workers, so they are easy to spot if you ever see one.


        1. Expert Member
          MALCOLM TAYLOR | | #18


          That's probably it. I'm still amazed - they seemed to have a switch they could hit and just die off all at once.

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