Do I Really Need a Three Inch Termite Inspection Gap?

That little gap separating your rim joist from your foundation block. Do you really need it? The answer really depends on where you live. Some localities require a termite gap to conform to building code.

Other places, don’t. But even if you live in a locale that does not require a termite inspection gap we recommend that you put one in regardless if you are able, and especially if you live in a region in which termites are known to be an issue (which is most places).

How Do Termites Travel in Crawl Space

But first what is a termite gap used for anyway? Well, to understand this you need to know a bit about termites and how they travel. Termites live and thrive in cold and damp places. They dislike light and avoid it at all costs. This is because, compared to their cousins, the ants, termite’s bodies are soft and fleshy – they lack the tough dark outer covering of chitin that ants typically have that protect them from the suns rays.

Termite bodies are often white or translucent and are easily damaged by the sun’s rays. Due to this fact, termites either wait until it’s dark to expose themselves, or they find a way to extend their lair by building tunnels.

Termite Tunnels in Crawl Space

Most often the case is that when termites are trying to establish themselves in the wood materials of your home they need to cross the space between the ground of your crawlspace or basement floor, and the wooden materials above such as your floor joists or rim joist. Crossing this expanse for a termite is risky because it leaves their soft vulnerable bodies exposed to light rays and predators.

To protect themselves termites will typically try to establish a network of tunnels spanning from their lair below ground and into the wood materials above. They do this by chewing up bits of dirt and mud and other materials and regurgitating it to form a sort of plaster or clay from which they form their tunnels.

These tunnels are the visible signs that tell the inspector that you have a termite problem. And normally without the termite gap you wouldn’t see the tunnels.

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16 thoughts on “Do I Really Need a Three Inch Termite Inspection Gap?”

  1. Hey Bro,

    It seems like by putting plastic on the crawlspace wall, even with a 3″ gap at top, it invites termites to nest behind the plastic and potentially find cracks in the block leading to the wood structure. This activity would not be noticed as it would be occurring out of human site behind the plastic.

    Sincerely trying to avoid unintended consequences. Thanks, Daniel

    1. Great statement, keep in mind you don’t have to take the plastic up the wall more than 12 inches but you must fasten it to the wall per code if you are closing the crawl space. We take it further up the foundation walls because moisture can penetrate and even flood the plastic in certain areas. Since we do it this way, local states with termites require a termite gap for the viewing of activity you described.

  2. Hi, good video, thanks for the info. If I leave a termite gap in a crawlspace built with CMUs where the sill plate doesn’t cover the entire CMU, how do I cap the CMU wall to seal moisture from coming up out of the CMU ‘holes’? Do you carry a product for that? Or should I use treated lumber and attach it to the top of the CMU wall with construction adhesive?

    1. Thank you and great question. For those reading your question a CMU is a Concrete Masonry Unit (similar to Cinder block wall). You can certainly use pressure treated wood although we typically us a termite resistant foam board with spray foam when addressing that situation.

  3. Hello, thank you for your videos! We are currently DIYing our crawlspace and wondering about the gap between the top of the cinder blocks where the wood sits on it. We can visibly see sunlight from outside and it’s about 1/4 to 1/2 wide. Can we use Great Stuff to close this gap? We have a French drain and a sump pump.

  4. Recently bought a house with an encapsulated crawl space with great headroom (about 4 feet). Called an exterminator to ask about termite warranty (had one for years at previous house). The guy said the sill is uncovered per code (good) but they would need to remove a 4″ strip of the insulation near the bottom of the wall, to treat and to inspect ensuring termites don’t go up the walls behind the insulation. Does this ruin the encapsulation? Have you ever heard this before?

    1. In my opinion it does ruin the encapsulation and we have not had a pest control company recommend this that I am aware of. I have not seen that as code requirement so may just be their company policy. I would suggest a second opinion and if you get same answer, that may be a local code requirement but seems like an odd thing to require. Sorry and hope that helps.

  5. Any suggestion on what to do about the cold air coming in with the 3 inch termite inspection gap? Our house is freezing since we encapsulated and removed the subfloor insulation, which the guy suggested…

    1. Have you tried air sealing sub-floor penetrations and the sill plate gap? Check pest control company to make sure you don’t void their warranty on sealing sill plate gap. Hope that helps.

  6. Houston Patrick

    Hi Michael. Thank you for your Youtube videos. I have approx 7 yrs left on a 10 year termite plan after my house with a crawlspace was treated for termites in July 2020. I understand about leaving the termite gap to allow for termite inspectors to see any possible termite channels. What, if any, are the cons (related to termites and termite warranty plans) with insulating the rim joist, especially with the use of foam board and caulk and/or spray foam around the edges of the foam board?
    Thanks again for all your videos.

    1. Hi Houston, unfortunately your pest company can set their own rules on what is or is not covered under warranty if the crawl space is encapsulated. We have some pest companies that will void a termite warranty if plastic is located anywhere on a foundation wall, although code says 3 inches is acceptable for a termite gap. I would certainly ask them for guidance on how to proceed so you do not void that warranty. Hope that helps.

  7. Hi Michael,

    We recently had a company do our encapsulation. The owner (who performed the assessment) said they’d run vapor barrier up the wall part way and then apply foam board insulation over it. Instead,, the finished product is foam board (R10) on the cinderblock walls and the 20 mil vapor barrier running all the way up the foam board and taped off at the top with waterproof tape. Is this an issue for moisture or termites? The vapor barrier is not sealed against the foam board other than being taped at the top.

    Thanks so much for all the helpful info on here and YouTube!

    1. We have had instances where we installed foamboard and vapor barrier the same way on a stone or brick wall. It is not the ideal situation but it is effective. If it was a block or concrete wall, we would typically take the plastic up-and-over the foamboard and attach it directly to the wall.

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