How to Keep Bugs and Critters Out of Your House
Having an airtight house is good in many ways. Last week I wrote about seven of them. And shortly after the article went out into cyberspace, three people emailed me or commented in the article about a glaring omission from the list: keeping bugs and critters out of the house. They were absolutely right. So let me add that reason for airtightness in a separate article.
How do critters get in?
Look at the photo above. Those are camel crickets—also called cave crickets—heading for a hole. If you live in a house with a crawl space or basement foundation, you may have seen these guys inside your house. And you’ve almost certainly been in a bathtub with them just inches away from you.
Bathtubs over crawl spaces and basements nearly always have a huge hole in the subfloor, as you can see above. Camel crickets love dark, damp places, so it’s perfect for them. Next time you take a bath or shower, try not to think about the dozens of them that could be just on the other side of that enameled surface.
So bugs can use the same holes that let unconditioned air into the house or expensive conditioned air out of the house.
Buffer spaces
Bugs and critters can get into your house through exterior walls, of course. But the buffer spaces are likely the biggest sources, especially if you live in an older house that didn’t have to meet any airtightness requirements when it was built.
And don’t think that the bathtub itself will keep you from seeing them. The underside of the tub is often connected to interstitial spaces that allow them to find ways into your bedroom. Not many people wake up with a horse’s head in their bed (as occurred in the movie The Godfather). But those air and bug leakage pathways could put a spider in your bed. I slept with the one below back in 2018 in a motel in South Dakota. (I also slept with a scorpion in Florida one time, but that had nothing to do with air and bug leakage. I inadvertently brought it in after drying sheets under a tree in the yard.)
Of course, the best way to keep buffer space critters out of the living space is to bring the buffer space indoors. You do that by encapsulating the crawl space or attic. It doesn’t mean you won’t have critters, but it does make it less likely.
A caution and an additional benefit
To make your air barrier work for bugs and critters, you may need to take some additional measures. Termites, for example, can tunnel through foam to get to the wood they crave. That’s why foundation insulation usually includes a termite shield in warmer climates.
Likewise, rodents and other critters can chew through foam, caulk, and other air sealing materials, so you may need to add hardware cloth or sheet metal. They also can squeeze through holes much smaller than you might imagine. The video below shows them going through a gap that’s only 14 mm across!
Keeping critters out with air sealing also has a side benefit. You do it without toxic pesticides. That helps with your indoor air quality and keeping children and others safe from accidental exposure to harmful chemicals. See the Cornell page on integrated pest management for more. (Thanks to Armand Magnelli for this link!)
So do some air sealing and you’ll improve your home in at least 8 ways! The 7 I wrote about last week, plus this one.
Allison A. Bailes III, PhD is a speaker, writer, building science consultant, and the founder of Energy Vanguard in Decatur, Georgia. He has a doctorate in physics and is the author of a bestselling book on building science. He also writes the Energy Vanguard Blog. For more updates, you can follow Allison on LinkedIn and subscribe to Energy Vanguard’s weekly newsletter and YouTube channel.
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We renovated a cabin a few years ago which was full of mice. If the holes are big enough for mice, they’re big enough for snakes. We found two 40″+ sheds in the attic.
Good point, John. And if mice are going through the hole, snakes may well be following them for a meal.
Nice article. I like how it connects airtightness and bug control (not just pest spray). One tip I’d add: when you seal up gaps, also use metal mesh or hardware cloth over vents or crawl space openings — critters can chew through caulk or foam but not metal. Also, check places you might forget, like under bathtubs or around rooftop penetrations — bugs often sneak in through those buffer areas.
I can attest to closing up every nook and cranny. On my 1903 Vic, it took many many tubes of caulk and foam and many hours but it was worth it. Combining those with stainless “steel wool” scrubbing pads helps too.
I am still looking for a closed cell foam which I can easily apply to OVERHEAD surfaces without the darn stuff getting all over me, floor, walls, in short everything except what it is supposed to adhere to. Good Stuff is great for horizontal surfaces, sticks to everything that gravity holds it to, but overhead it has an amazing ability to just stick where I do not want it. Any suggestions?
Mice or rats got into my garage under the old garage door. So, I placed bricks inside and outside of the door where there were slight gaps underneath, and I installed Simpson Strong Tie brackets onto the outside of the bottoms of the garage door frames since the concrete was slightly worn away there. I also put stainless steel wool in gaps by the chimney, since I found that steel wool rusted and could stain the siding. Then I put small containers with a few peanuts in them into my garage and basement to signal if there were any rodents coming in — to see if they were eaten. None have been in since. Another suggestion — if setting traps, attach a piece of copper wire to the metal loop on it and tie it to something to secure it in place. About 50 years ago a mouse trap disappeared, and about 20 years ago I found a dried-out mouse or small rat still in it, underneath some shelves in my basement.