How to Seal a House Against Pests: Exclusion Materials and Where They Go

October 09, 2026 · Regional Pest Guide Team · pest-prevention home-exclusion

Find the Gap Before You Buy the Material

A pest problem that keeps coming back is usually an entry-point problem, not a treatment problem. Mice can flatten their skulls and squeeze through a gap about a quarter inch wide, roughly the width of a pencil. Rats need closer to a half inch. Ants and other crawling insects use smaller openings still: hairline cracks in mortar, the gap where a dryer vent meets siding, the quarter-inch reveal under a garage door.

Before buying any sealing material, walk the exterior and note what kind of gap you’re dealing with. A pipe penetration needs a different fix than a foundation vent, and a foundation vent needs a different fix than the gap under a door. The four sections below sort by gap type, not by pest, because the same half-inch hole around a hose bibb lets in mice, ants, and the occasional spider.

Steel Wool and Copper Mesh for Pipe and Wire Penetrations

Anywhere a pipe, cable, or conduit passes through an exterior wall, there’s usually a gap left over from the original installation. These openings are often less than an inch across, which makes them easy to miss and easy for a mouse to use.

Steel wool packed tightly into the gap works because mice won’t chew through it; the fibers aren’t rigid enough to collapse under their teeth but are too sharp to gnaw past comfortably. Copper mesh does the same job and holds up longer outdoors since it doesn’t rust. Pack either material in firmly enough that it can’t be pulled free from the outside, then caulk over the top to keep water out. Skip plain fiberglass insulation here: it insulates but doesn’t resist chewing, so it slows a rodent down for an evening at most.

For a broader walkthrough of where rodents find these openings room by room, see winterizing your home against rodents.

Hardware Cloth for Vents, Weep Holes, and Foundation Gaps

Larger openings, foundation vents, crawl space access doors, weep holes in brick veneer, call for something stiffer than mesh. Quarter-inch hardware cloth, cut to size and screwed or stapled over the opening, blocks rodents while still letting the vent or weep hole do its job of moving air and moisture.

Chicken wire isn’t a substitute here. The gaps in chicken wire run an inch or more, wide enough for a mouse and in some cases a young rat. Hardware cloth with a true quarter-inch grid is the material that actually matches the gap size you’re defending.

Garages get skipped in this step more than any other area of the house, because the gap between a garage door and the slab often isn’t noticed until droppings show up along the wall. A full garage-specific checklist is here: how to rodent-proof your garage.

Expanding Foam and Caulk: Two Different Jobs

Foam and caulk get treated as interchangeable, and they aren’t. Expanding foam fills volume: use it for gaps deeper than about a quarter inch, around larger conduit runs, or behind siding where you can’t see how far back the opening goes. Standard foam does swell enough for a mouse to chew a new path through it once it cures, so for rodent-specific gaps, look for a foam labeled as pest-block or rated for rodent resistance, or back it with steel wool first and foam over that.

Caulk is for surface-level cracks, not volume. Use exterior-rated silicone or polyurethane caulk on hairline gaps in siding, around window and door trim, and where two building materials meet and create a seam. Caulk alone won’t stop a mouse through anything wider than a pencil lead, but it closes the smaller cracks that ants, and in warmer climates certain roaches, use to get past the siding.

Perimeter trails along a foundation are usually ant activity rather than rodent activity, and the fix is sealing the crack line, not treating the soil. For the broader set of exclusion and monitoring tactics for ants specifically, see ant control strategies.

Door Sweeps and Garage Gaps at Ground Level

Exterior doors settle over a few years, and the gap at the bottom grows past the quarter-inch threshold without anyone noticing until cold weather pushes pests indoors looking for warmth. A door sweep, a strip of rubber or brush fastened to the bottom of the door, closes that gap without affecting how the door opens and closes.

Garage doors need a different product: a bulb-style weatherseal along the bottom edge, rather than a sweep, since garage doors don’t swing the way entry doors do. Check the seal at both ends of the door track, not just the center. Gaps at the corners, where the seal meets the track, are a common miss and a common entry point.

Where to Start This Fall

If you only have time to seal one thing before the weather turns, start with whichever gap is largest, since that’s the one giving the widest range of pests access at once. For most houses that means the garage door seal or a foundation vent, not the smaller pipe penetrations. Work from largest gap to smallest, and recheck the work after the first hard rain, since caulk and foam both reveal gaps they missed once water finds them.

For a full rundown of what else to check as temperatures drop, see your fall pest prevention checklist, region by region.

🏡 More from EPM Labs: