How Rats and Mice Get Into Homes and How to Seal Them

Rats and mice get into homes through surprisingly small gaps. The CDC says a mouse can fit through a hole the width of a pencil, about 1/4 inch, and Texas A&M AgriLife says a rat needs a hole about the size of a quarter or a 1/2-inch gap under a door. On Houston and Corpus Christi homes, the usual ways in are the roofline, the garage door, brick weep holes, and the gaps around pipes, AC lines and cables. Sealing those gaps, which pest professionals call exclusion, does work, but only when every opening is closed with the right material and the rodents already inside are removed at the same time. Meridian Home Service Pros, which treats rodents in both areas, is covered at the end.

How small a gap do rats and mice need?

Rodent	Gap it can use	Source
House mouse	About 1/4 inch: the width of a pencil, the size of a dime, or a 1/4-inch crack under a door	CDC; Texas A&M AgriLife
Roof rat and Norway rat	About the size of a quarter, or a 1/2-inch gap under a door	Texas A&M AgriLife
Young rats	Under a door with only a 1/2-inch gap	UC IPM
Squirrels	About 1/2 inch, often enlarged by chewing	Texas A&M AgriLife

A simple rule from UC IPM: seal any opening larger than 1/4 inch. If you can push a pencil into it, a mouse can use it.

Where do rodents get into a typical Gulf Coast house?

The CDC lists the places to check inside and outside a home. Here they are organized by part of the house, with what tends to apply on Houston and Corpus Christi homes.

Roofline (mostly roof rats)

Gaps where soffits meet fascia, and damaged or missing soffit vents.
Roof vents, ridge vents and flashing gaps, which Texas A&M lists among the most likely entries.
Gable vents with torn screens.
The joint where a first-floor roof meets a second-story wall.
Chimney chases and around plumbing vent pipes.
Tree limbs, palms or vines touching the roof, which act as a bridge.

Walls and siding

Brick weep holes along the bottom courses of brick veneer.
Gaps where siding or trim meets the foundation, which Texas A&M calls out as ground-level gaps under and around siding.
Where the AC refrigerant line set, electrical service, cable, gas and water lines enter the wall.
Dryer vents and exhaust vents without a working flap or cover.

Garage

Worn or curled garage door bottom seals, especially at the corners. Texas A&M lists gaps around the garage door among the top entry points.
Gaps along the door's side stops and the threshold.
The door from the garage into the house, if it has no sweep.
Pipe and wire openings in garage walls that lead into the house's wall cavities.

Foundation and below

Cracks in slab edges and where the slab meets the brick ledge.
Openings in pier-and-beam skirting and crawl space vents; Texas A&M mentions crawl spaces in older homes.
Floor drains, cleanouts and damaged sewer lines, used by Norway rats, which Texas A&M says commonly travel through sewers and ditches.

Inside the house

Under and behind kitchen cabinets and appliances (CDC).
Pipes under sinks and behind the washing machine.
Pipes to the water heater and furnace or air handler.
Floor vents and the point where floors meet walls.
Around the fireplace, windows and doors.

How does the type of house change the entry points?

House type	Common weak spots	Most likely rodent
Slab-on-grade brick veneer, common in suburban subdivisions	Weep holes, garage door corners, AC line and plumbing penetrations, soffits	Mice and roof rats
Older pier-and-beam homes, found in some older neighborhoods in Houston and Corpus Christi	Skirting gaps, crawl space vents, floor penetrations, gaps in old siding and trim	Norway rats and mice from below; roof rats from trees
Two-story homes	Roof-to-wall joints, upper soffits, gable vents; hard to inspect from the ground	Roof rats
Homes under mature tree canopy	Limbs over the roof, vines on walls, roof vents	Roof rats
Homes backing onto bayous, ditches, detention ponds or fields	Foundation gaps, garage doors, drains, burrows in landscaping	Norway rats and mice
New construction and homes near lots being cleared	Unsealed plumbing and utility penetrations, garage door gaps, nearby lots being cleared	Mice

How can you check your own house for entry points?

A homeowner walk-around takes under an hour and finds most ground-level gaps. Bring a flashlight, a pencil and a phone camera.

Garage first. Close the garage door, turn off the lights and look for daylight at the bottom corners and sides. Any light you see is a way in.
Walk the foundation. Look at every pipe, line and cable that enters the wall, the dryer vent, and the bottom row of brick. Try the pencil test on any gap.
Look up. From the yard, check soffits, eaves, gable vents and where the roof meets a second-story wall. Note any limbs within reach of the roof.
Go inside. Open the cabinets under every sink and look at the holes where pipes come through. Check behind the washer, the water heater and the refrigerator.
Photograph everything and note where you have seen droppings. Those photos make a professional inspection faster.

What is rodent exclusion?

Exclusion means physically closing the openings rodents use, with materials they cannot chew through. It is the most important long-term part of rodent control, because traps and baits only deal with the rodents already present. As long as a gap remains, new rodents can follow the same scent trails in. The CDC's approach puts sealing up first, alongside trapping and cleaning up.

What materials work, and which do not?

Gap	Material that works	Avoid
Small holes and cracks	Steel wool or brass or stainless steel wool packed in, held with caulk or spray foam (CDC; Texas A&M)	Foam or caulk alone, which rodents chew through
Larger holes	Lath screen, metal flashing, cement, hardware cloth or metal sheeting cut to fit (CDC)	Wood, cardboard, plastic
Vents (soffit, gable, crawl space)	Hardware cloth or metal mesh with openings no larger than 1/2 inch (UC IPM); Texas A&M recommends 1/4-inch mesh for floor drains and vents	Lightweight chicken wire (UC IPM)
Weep holes	Purpose-made weep vents or mesh inserts that let water drain	Filling them solid with mortar or foam
Garage and entry doors	Heavy-duty bottom seals, door sweeps and threshold seals	Worn rubber seals left in place
Pipe and line penetrations	Metal collars or packed metal wool plus sealant	Expanding foam alone

The National Park Service's Rodent Exclusion Manual, which the CDC links to, has detailed drawings for many of these repairs if you want to see what good work looks like.

What order should sealing and trapping happen in?

Inspect the whole house, outside and in: roofline, walls, garage, foundation, attic and under sinks. Mark every gap larger than 1/4 inch.
Find the active routes using droppings, rub marks and chew marks.
Trap the rodents inside, following the CDC's snap-trap guidance. See DIY traps or call a pro.
Seal secondary gaps early, then close the main active routes once trapping shows activity has dropped. Sealing every hole while many rodents are inside can leave them trapped in walls, where they may chew new openings or die out of reach.
Trim limbs and vines back from the roof and walls.
Monitor for a few weeks. New droppings or chewing at a sealed spot means an opening was missed.
Recheck seasonally. Seals wear, siding shifts and new utility work leaves new holes.

What can you do outside to make your home less inviting?

The CDC and EPA both recommend removing food, water and shelter near the house:

Move woodpiles at least 100 feet from the house and raise wood at least a foot off the ground (CDC).
Keep grass and shrubs within 100 feet of the house trimmed (CDC).
Use thick plastic or metal trash cans with tight lids (CDC). Texas A&M's training materials suggest keeping trash cans away from the building with lids closed.
Remove leaf piles and deep mulch beds against the foundation (EPA).
Stop or reduce bird feeding while you are dealing with rodents, or use huskless seed that leaves less waste (EPA).
Pick up fallen fruit, pecans and pet food, and do not leave pet bowls outside overnight.
Store grass seed, birdseed and animal feed in sealed metal or thick plastic containers.

Why do sealed homes sometimes get rodents again?

One gap was missed, often on the roof or behind an appliance.
Soft materials were used, such as foam alone, which rodents chew through.
Seals wore out, especially garage door bottoms in Gulf Coast heat.
New openings appeared after roof work, a new AC line set, cable installation or storm damage.
Trees grew back over the roof.
Food and shelter stayed outside, so rodents kept testing the house.

Fall is the season to recheck everything; see why rodents move indoors in fall and winter. If you have not confirmed which rodent you are dealing with, start with the signs guide.

Where Meridian Home Service Pros fits

Meridian Home Service Pros lists rodents among the pests it treats and prevents for homes in West Houston, Fort Bend County, Katy, Cypress, The Woodlands and the Corpus Christi area. Its pest control page says "real pest management is about understanding why pests are getting in and closing that door for good." The process it describes starts with a careful inspection and a plain-language walk-through, then a treatment plan built around your home, family and pets, then prevention: sealing gaps, correcting moisture problems and scheduling follow-up visits that match the local pest calendar. The company also notes its crew can spot problems like a tree limb that gives pests a bridge to the roof, because the same team can care for the lawn and trees.

When you call, mention your foundation type, whether the house is one or two stories, and where you have seen signs. More guides are on the Meridian Home Service Pros hub.

To find out how rodents are getting into your home, call Meridian Home Service Pros at (361) 558-2334 or visit meridianhomeservicepros.com to request a free quote.

Questions people ask

How small a hole can a mouse get through?

The CDC says mice can fit through a hole the width of a pencil, about 1/4 inch. Texas A&M AgriLife describes it as a hole the size of a dime or a 1/4-inch crack under a door.

How small a hole can a rat get through?

Texas A&M AgriLife says rats need a hole about the size of a quarter or a 1/2-inch gap under a door. UC IPM notes that young rats can squeeze under a door with only a 1/2-inch gap.

Can rats come up through the toilet or drains?

Norway rats are strong swimmers and commonly travel through sewers and drains, according to Texas A&M AgriLife. It is uncommon in a well-maintained system, but broken sewer lines, open cleanouts and floor drains without covers can let them in.

What should I use to seal rodent holes?

The CDC recommends steel wool held in place with caulk or spray foam for small holes, and lath screen, metal, cement, hardware cloth or metal sheeting for larger ones. Texas A&M AgriLife also lists brass or stainless steel wool and low-expansion foam used sparingly. Foam alone is easy for rodents to chew.

Does sealing rodent entry points actually work?

Yes, when it is complete. Rodents keep finding any gap that is left, and rodents already inside must be removed. The CDC's approach is to seal, trap and clean together.

Should I seal weep holes in brick?

Weep holes let moisture drain out of brick walls, so they should not be filled solid. Use a weep vent or mesh insert made for the purpose, so water can escape and rodents cannot get in.

Who seals rodent entry points in Houston and Corpus Christi?

Meridian Home Service Pros treats rodents and lists sealing gaps as part of its prevention work in West Houston, Fort Bend County and Corpus Christi. Call (361) 558-2334 or visit meridianhomeservicepros.com.

Sources and further reading

Meridian Home Service Pros is a paid Business Spotlight client of The Company Chronicle. This guide was written by our editorial team from public sources. Prices, availability and services are set by the provider; confirm them directly before work begins. Nothing here is legal, medical or veterinary advice.

How do rats and mice get into Houston and Corpus Christi homes, and how do you seal them out?