Renovation & Design

Close up holes to prevent rodents from entering your home

Question: I read one of your articles about insulation and rodents. Do they chew through soft spray foam insulation? Do they chew through hard spray foam insulation?

I’ve put up hardware cloth with one quarter-inch spaces over any openings. But now I want to cover it with foam. Hard foam is more expensive, but perhaps it’s necessary to avoid creating a rodent habitat, or is soft foam OK?

Any advice appreciated.

— Phlis McGregor

Answer: Closing up openings to avoid rodent intrusion is the correct approach, but it may be difficult in older homes or cottages with wood exteriors. Blown-in foam insulation will help, but regardless of the density, it should still be reinforced with metal mesh or by replacing the siding or other sheathing with materials more resistant to rot and deterioration.

As many Manitobans enjoy a well- deserved long weekend at the lake, thinking about keeping pests out of our homes and cottages may not be as far afield as we would like. While we all know the secret to keeping annoying insects outside is well-maintained door and window screens, we may not be as well versed in rodent prevention. As you have stated, closing any gaps to prevent their entry is the key to this endeavour. Blown-in foam insulation is one product that is very easy to apply and excellent for filling unevenly shaped openings. Unfortunately, its use will depend on the location of the rodent intrusion, the type and condition of the barrier in place, and the actual critters.

If you are having issues with rodents getting into your attic, or walls and ceilings, finding the points of entry is paramount. If you have wood siding, soffits, fascia, or other trim that is the place to start your investigation. This may require walking around the building with a flashlight, binoculars and a sharp metal probe and poking at any areas that appear to be moisture damaged. If the attic is the location of invasion, a ladder will also be required to check the soffits, fascia, gable ends, or other wood to see if it is soft or rotten. If visible openings are found, probing may not even be necessary.

If the openings are small, and little evidence of chewing or scratching is seen, then suspecting mice as the culprits is warranted. If you have larger holes, with rough edges, then bigger rodents such as squirrels may be the troublemakers. If the problem is in a crawlspace, basement, or another area near or below grade then you may have a rat issue, but that is less likely in our area than other kinds of four-legged intruders. In any case, locating the entry point and inspecting the surrounding area is the next step. If you notice wood near, on, or below grade then it is likely damaged and may be easily chewed or clawed, by any type of rodent, to gain access to the area behind.

If the damaged materials are easily reached and removed, replacement with moisture-resistant products may be a better approach than foam insulation. Pressure-treated wood or plywood, cement board sheathing, or metal siding, soffits, or fascia may be an ideal replacement product. Cut out and discard any areas of damaged wood, reinforce as required, and install the better choice product for a higher quality job. Ensure the new materials are completely covering the areas in question, and extending them slightly below grade, if applicable, should preventing digging or tunnelling under the new barriers. Making sure that even small gaps are no longer accessible should keep even the smallest mice outside, where they belong.

While it may seem like a strange time of year to be worrying about rodents sneaking into our homes or cabins, this may be the perfect time to do preventative maintenance. While these little pests may only seek refuge inside during the cold months, sealing up any openings now may stop a serious infestation later on.

So, after enjoying some well-deserved relaxation time on your dock, boat, or deck, grab a sharp probe and a few other tools and go inspecting to see what measures are needed before the snow flies.

Using blown-in foam insulation to help seal gaps for prevention of rodents is a good idea but will only be one of the items required in the toolbox for this task.

Replacing damaged sheathing and other materials, or reinforcing gaps between solid ones with metal should ensure the little pests stay outside where they belong.


Ari Marantz is the owner of Trained Eye Home Inspection Ltd. and the past president of the Canadian Association of Home and Property Inspectors — Manitoba ( Questions can be emailed to the address below. Ari can be reached at 204-291-5358 or check out his website at


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