How do rats and mice get into the attic?
Through openings in the house: vents with weak or torn screens, gaps at the eaves and roof, and holes where pipes and wires come in. Many get in low, through the crawl space or garage, and climb up inside the walls.
Rodents don’t need a big hole. They need a gap they can squeeze through or chew a little wider, and a reason to come in, like warmth, shelter and food nearby.
How small a hole can a mouse or rat fit through?
A mouse can fit through a hole about 1/4 inch wide, the width of a pencil, according to the CDC. Rats can squeeze under a door with a half-inch gap.
UC Integrated Pest Management recommends sealing every hole larger than 1/4 inch to keep out both. That is why a proper job closes the small gaps too, not only the obvious holes.
Where are the most common entry points?
These are the openings we check on every inspection. The CDC lists most of the same places.
- Foundation and crawl space vents. Old screens rust, tear or get pushed in.
- Roof and gable vents. Easy to reach for roof rats and squirrels.
- Eaves and soffits. Gaps where the roof meets the walls.
- Roof gaps. Spots where roof lines meet or flashing has pulled away.
- Pipe, wire and AC line entries. Gaps around anything that passes through a wall.
- The garage. Gaps at the corners of the garage door and openings that lead into the walls.
Can rats climb walls and get on the roof?
Roof rats can. UC IPM calls them more agile and better climbers than Norway rats, and notes they often run along utility lines and fence tops at night.
Trees and ivy close to the house give them an easy path to the roof. This is common in leafy Bay Area neighborhoods, from Menlo Park to older streets in San Jose. Trimming branches back from the roof helps, but the openings still need to be closed.
Can rodents get in through the crawl space or garage?
Yes, and it is one of the most common routes. Rats and mice get under the house through a weak foundation vent, then follow pipes and wall gaps up toward the attic.
The garage is similar. A gap at the corner of the door is enough for a mouse, and from there the walls lead everywhere. That is why we never inspect only the attic. If rodents have been living under the house, the crawl space may need cleanup too; see crawl space cleaning.
What do you seal the openings with?
Galvanized steel mesh, putty and concrete. Rodents chew through soft materials, so we use materials they can’t chew through.
UC IPM warns that rats can chew through plastic, wood and caulk, and recommends galvanized metal mesh over vents instead of lightweight chicken wire. Our approach follows the same idea: mesh screwed over vents and openings, putty to close the edges and gaps around pipes, and concrete where the opening calls for it. You can read more in why we seal with mesh.
How can I check my own house for entry points?
Walk around the outside of the house in daylight with a flashlight, then check the garage. You won’t find everything, but you will get a good idea of what is going on.
- Look at every foundation vent. Screens should be whole, tight and free of rust holes.
- Look up at the eaves, the gable vents and the roofline for gaps, chewed edges or loose screens.
- Check where pipes, wires, the gas line and AC lines go into the walls.
- In the garage, look at the bottom corners of the door and along the base of the walls for daylight and droppings.
- Note branches, ivy or fences that touch the house.
Roof openings and the inside of the attic are harder and riskier to check yourself. That part is what the free inspection is for.
Why does sealing work better than traps alone?
Traps remove the rodents already inside. Sealing stops new ones from coming in. You need both, in that order.
If you only trap, the openings stay open and the next rats move in. When every way in is sealed first, the traps only have to catch the ones left inside. We set traps after sealing (snap traps for rats and mice, live traps for larger animals like raccoons and squirrels) and come back at least two weeks later to check them.
Can rats get back in after the house is sealed?
Not through the openings that were sealed with mesh, putty and concrete. New gaps can still appear later, so it is worth knowing what to watch for.
Most new openings come from other work on the house: a new cable or solar line drilled through a wall, a roofer lifting the edge of the roof, or a vent screen removed and not put back. If you hear noises again after work like that, call us. Rodent proofing comes with a warranty, written on your invoice, and the office can walk you through what it covers.
What we see on real jobs
On inspections around Mountain View and the rest of the Bay Area, the entry points are rarely a surprise, but there are almost always several:
- Foundation vents with rusted or torn screens.
- Gaps around pipes and AC lines where they enter the house.
- Openings at the eaves and roof, often close to trees.
- Earlier patch jobs done with soft materials that have been chewed through.
We photograph every opening we find, so you can see each one before the work starts. Book a free inspection, and we will check the attic, crawl space, garage and the outside of the house and send a written quote the same day.