The short version: five items handle nearly every gap on a house. Exterior-grade caulk for cracks, copper mesh or steel wool for holes around pipes, a can of foam for big voids, a garage door bottom seal, and door sweeps. The one rule that separates a seal that lasts from one mice chew back through: never fill a rodent-sized hole with foam or caulk alone. Pack it with metal mesh first. This page is the how. We cover why sealing beats spraying on its own page.
This is the doing guide, not the case for it. If you want the reasoning, the argument that a sealed wall protects a home better than a wet one, that lives on why sealing beats spraying. Here we skip straight to the parts list, the gap-by-gap walk, and how to make each fix hold in a valley that bakes caulk in summer and cracks it in winter.
The five-item sealing kit
You do not need a truck full of supplies. Almost every opening on a house falls to one of these five, all available at any Treasure Valley hardware store.
- Exterior-grade silicone or polyurethane caulk. For cracks and seams up to about a quarter inch. It flexes with the house and shrugs off sun and cold better than cheap latex.
- Copper mesh or stainless steel wool. The workhorse for holes around pipes and wires. Rodents cannot chew through the metal fibers, and copper will not rust and streak the wall.
- Expanding foam. For filling large voids and dead air, always packed over mesh where a rodent could reach it.
- A garage door bottom seal. The single highest-value part on this list, because the garage door is the widest gap on most homes.
- Door sweeps and weatherstripping. For the daylight under and around every exterior door.
Add a roll of quarter-inch hardware cloth and a few weep hole covers if your house has open vents or brick, and the kit is complete.
Where the gaps hide
Do one slow lap of the foundation with the flashlight, low and close, checking these in order. On a house, pests come in low and near utilities far more than through a wide-open door.
- Utility penetrations Every place a pipe, spigot, gas line, electrical conduit, cable, or AC line-set passes through the wall. These are the number one structural entry point, because the drilled hole is almost always bigger than the pipe. Check the dryer and bathroom exhaust vents too, where the flap often no longer closes.
- The sill and foundation seam The long horizontal line where the wood framing sits on the concrete foundation, and the joint where the siding starts. Settling opens hairline gaps here that run the length of the house.
- Weep holes and vents The small openings along the bottom course of brick and the louvered foundation or crawl space vents. These stay open on purpose, so they get screened, not filled.
- The garage The bottom seal, the side and top weatherstripping, and the service door. On most Treasure Valley homes the garage is the entry room, so give it the most attention and see how to pest-proof your garage for the full version.
- Doors and windows Worn door sweeps, gappy thresholds, torn screens, and the often-forgotten door between the garage and the house.
- Up high Roofline soffit gaps, fascia joints, and the spots where cable or satellite lines enter under the eave. Easy to forget from the ground, and a favorite route for mice that climb.
Match the fix to the gap
The trick is using the right material for the size and type of opening, so it holds instead of popping loose in a season.
- Hairline cracks and seams: a clean bead of exterior caulk, tooled smooth so nothing can pick at the edge.
- Round holes around pipes: pack copper mesh or steel wool firmly into the gap, then cap with caulk or a pipe collar. This is the standard fix and it beats foam alone every time.
- Large voids and rough openings: mesh first, then expanding foam, trimmed flush and covered once cured so sunlight does not chew it back apart.
- Weep holes and vents: stainless weep hole covers or a piece of hardware cloth cut to fit and secured over the opening. Never caulk these shut.
- Under doors: a new sweep set so it just kisses the threshold, plus a fresh garage door bottom seal at the widest gap of all.
The rodent rule
Here is the one thing that separates a professional-grade seal from one that fails in a month. A house mouse squeezes through a gap the size of a dime, roughly a quarter inch, and a rat needs only a half inch, about a quarter coin. More important, a mouse will chew a small gap into a big one, straight through foam, wood, drywall, and soft plastic. So any opening a rodent could use gets metal in it: copper mesh or steel wool, packed tight, before you caulk or foam over the top. The metal gives them nothing to gnaw and nowhere to gain a purchase. Skip this step and you have sealed the hole against insects but left the door open to mice. If you are chasing an active mouse problem, pair this with the trapping and monitoring in rodent control and the full plan in how to keep mice out of your house.
Not sure you found every gap? A trained eye catches the ones a flashlight misses.
Get a Free Quote →Mistakes that undo the work
A few common errors turn a good afternoon into wasted effort.
- Caulking weep holes and vents shut. It traps moisture in the wall and starves the crawl space of airflow. Cover, do not seal.
- Foam without mesh in a rodent gap. It looks finished and buys you about two weeks before a mouse tunnels through.
- Sealing a hole with something living behind it. If a wall void has an active nest, trap or clear it first, or you trap the problem inside where it dies and smells.
- Ignoring the top of the house. Soffit and roofline gaps are out of sight, and climbing mice and wasps use them all the time.
- Doing it once and forgetting. Recheck the wear points, sweeps, weatherstripping, and cracked caulk, once a year.
Sealing is one pillar of a bigger routine. See how it fits with moisture, yard, and food habits in the home pest-proofing checklist.
Sealing questions
What is the best material to seal gaps against mice?
Copper mesh or stainless steel wool packed tightly into the gap, then capped with caulk or foam to hold it in place. Rodents cannot chew through the metal fibers the way they gnaw through foam, wood, or plastic alone. For gaps around pipes this combination is the standard exclusion fix. Copper mesh is worth the small premium over steel wool because it will not rust and stain the wall.
Can I just use expanding foam to keep pests out?
Foam is fine for filling large voids and blocking airflow, but not on its own where rodents are a concern, because mice chew right through it. Pack the opening with copper mesh or steel wool first, then foam over it. Foam also breaks down in sunlight, so any bead exposed on the exterior should be trimmed and covered with caulk or a proper cover once cured.
Should I seal the weep holes in my brick house?
No. Weep holes are the drainage and ventilation path for the wall cavity, and caulking them shut can trap moisture and cause real damage. Use purpose-made weep hole covers or stainless mesh inserts instead. They let the wall breathe and drain while keeping out wasps, mice, and the spiders and box elder bugs that shelter in the gaps.
How do I find entry points I cannot see?
Two tricks. In daylight, stand inside a dark garage or basement and look for pinpoints of light coming through the wall, which mark open gaps. At dusk, run a flashlight along the foundation from outside and watch for shadows at pipe penetrations and the sill line. Following an actual pest trail, like an ant line or the greasy rub marks mice leave, points you straight at the opening they favor.
Is sealing a house a one-time job?
Mostly, but not entirely. A good seal lasts years, yet houses settle, caulk cracks in the Treasure Valley's temperature swings, and door sweeps and weatherstripping wear down. Walk the perimeter once a year, ideally in early fall before rodents move in, and touch up what has opened back up. The big penetrations rarely need redoing, but the wear points do.