I'm endlessly revising my perimeter footing insulation project and need to know: how far below grade do subterranean termites tunnel? These would be normal subterraneans, not formosans. For some reason, my search-fu is failing and I cannot seem to find this information anywhere online.

  • 1
    If you are planning to use the insulation as a barrier for termites, you may be fighting a lost battle. I believe your best bet is to seal the foundation to the framing, and seal the framing against termites before the insulation goes on, otherwise the insulation will be a freeway to your framing, as you may know already.
    – Jack
    May 19 '14 at 3:39
  • No, I'm planning on using a termite-impenetrable material, such as metal or 16-grit sand, and I'm hoping to discover how deep it needs to go. The insulation will be protected behind this barrier. Finally, a termite inspection gap above the footing insulation but below the cladding will be left uncovered.
    – iLikeDirt
    May 19 '14 at 13:44
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    If you are in the US, call your agricultural extension office. They will know, or know who knows. In other parts of the world, the equivalent resource may be university affiliated.
    – user23752
    Aug 3 '14 at 20:11

According to this paper from the University of Nebraska, they can go up to 20 feet in the ground:

Subterranean termites are ground-dwelling social insects living in colonies. The two species found in Nebraska have similar habitats. These termites have the ability to adjust the depth of their colony (nest) in soil depending on temperature and moisture requirements. The colony may be 18-20 feet deep in the ground.

http://digitalcommons.unl.edu/cgi/viewcontent.cgi?article=2159&context=extensionhist (PDF Link)

The paper goes on to say that the species they observed are local to Nebraska, however I think it demonstrates these things can dig deep, probably deeper than you can make a barrier. Other less-reliable sources cite depths up to 40 feet.

  • Certainly that is likely enough to change tactics altogether. The OP should put insect proofing on the outside of the structure.
    – wallyk
    Aug 4 '14 at 4:24

I've been in the pest control & termite industry for 33 years, all the literature & continuing education Books say the main nest could be 20-40 ft Below the soil level.


Dig and see where the water level. They can not go beyond that pount.

  • Hello, and welcome to Home Improvement. Thanks for the answer; keep 'em coming. And, you should probably take our tour so you'll know the details of contributing here. Mar 5 '20 at 21:54

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