Quick answer
Pest entry points are the gaps, cracks, holes and openings in a building’s outer shell that insects, rodents and other animals use to get inside, such as gaps under doors, holes around pipes and wires, open vents and torn screens.
Some are only a sixteenth of an inch wide, and finding and sealing them is called exclusion, and it is the main way to keep pests out instead of treating them once inside.
Quick facts
The key facts about Pest Entry Points, with sources:
- Smallest gap for insects
- About 1/16 inch can let insects and spiders in 4
- Seal rule for rodents
- Seal all holes larger than 1/4 inch to keep out rats and mice 3
- Young rats under doors
- Can squeeze under a door with a 1/2-inch gap 3
- Vent covers for rats
- Galvanized metal with 1/2-inch mesh; not chicken wire 3
- Plant clearance
- EPA: keep vegetation, shrubs and mulch at least 18 inches from the house 5
- Best time to seal for insects
- Fall, before insects look for winter shelter 4
Key takeaways
- Most pests walk, crawl or fly in through ordinary openings in the outer shell that you can find, measure and seal.
- Gap size decides which pests fit: about 1/16 inch for insects, 1/4 inch for mice, a little more for rats.
- The most common spots are under doors, around pipes and wires, vents, screens and the foundation line.
- Rodents chew through foam, plastic, wood and caulk alone, so rodent holes need metal or concrete.
- Sealing usually lasts longer than repeated treatment, but it does not remove pests that are already inside, so removal comes first.
What counts as an entry point
An entry point is any opening from outside to inside that a pest can fit through. Some are obvious, like an open door or a torn screen, but most are not: a gap where a cable enters the wall, a missing strip of weatherstripping or a crack where the siding meets the foundation is enough.
Pest professionals talk about the “building envelope”: the outer shell of walls, roof, foundation, doors and windows. Every place a pipe, wire, vent or duct passes through that shell is a planned hole, while every crack, worn seal or damaged board is an unplanned one, and pests use both.
The CDC’s rodent checklist shows how many there are. Indoors it lists cabinets, closet corners, fireplaces, appliance backs, pipes under sinks, dryer and floor vents, utility lines, attics, crawl spaces, floor drains and the line where floor meets wall.
Outdoors it adds roof edges, eaves, soffits, vents, the foundation line and holes for utility lines 1.
Sealing these openings is called pest exclusion, and it is the long-term answer to most of them.
How pests find and use entry points
Pests do not find gaps by luck; each one follows cues of warmth, scent and shelter that lead it to the shell of a home.
- Drawn by warmth, food or shelter. Many insects gather on warm south- and west-facing walls in fall as they look for a place to spend the winter 4.
- Follow edges. Mice and rats prefer to run along walls and foundations, where they soon meet any gaps at the base of the house.
- Climb. Openings high on the house matter too, because roof rats and house mice are good climbers that reach eaves and roof vents 32.
- Squeeze or chew. A mouse can fit through a hole about 1/4 inch across 1, while rats chew plastic, foam, wood and caulk to widen a gap 3.
- Settle in voids. Once inside, pests use wall voids, attics and crawl spaces to nest, often far from the gap where they entered.
- Yard and plantsShrubs, mulch and woodpiles near walls give cover
- Foundation linePests travel along the base of the house
- Gap found1/16 inch for insects, 1/4 inch for mice
- Inside the shellWall voids, attics, crawl spaces
- Living spaceKitchens and bathrooms with food and water
Each stage is a chance to stop pests: clear the yard edge, seal the gap, then deal with anything already inside. Source: [4] [1] [5]
Common entry points and the pests that use them
| Entry point | Typical pests | Usual fix (per source) |
|---|---|---|
| Gap under exterior doors | Insects, spiders, mice, young rats 43 | Door sweep that touches the ground; tight threshold 43 |
| Holes around pipes, wires, cables | Mice, rats, cockroaches, ants 1 | Steel wool plus caulk for small holes; metal or cement for large 1 |
| Foundation cracks | Mice, rats, ants 2 | Metal or concrete for rodents 2 |
| Attic, roof and crawl space vents | Rats, mice, insects 3 | Galvanized 1/2-inch mesh for rodents 3 |
| Torn window screens | Flying insects 5 | Repair or replace screens 4 |
| Floor drains | American and Oriental cockroaches 6 | Screens on floor drains; keep water in traps 56 |
| Eaves, soffits, siding gaps | Roof rats, fall-invading insects 34 | Repair damaged sections 4 |
| Chimney | Rats and other animals 3 | Spark arrester cap 3 |
| Packages, birdseed and dry goods | Pantry pests and hitchhikers 54 | Check items before bringing them in 5 |
The last row is a reminder that not every entry point is a hole, since German cockroaches and bed bugs often arrive in bags, boxes and secondhand furniture.
Example: matching gap size to the pest
This example uses only published measurements. It shows why one gap can be fine for a rat but open to an ant, and why the fix depends on the pest you are keeping out.
| Gap you measure | What can fit, per source | What it means for the fix |
|---|---|---|
| 1/16 inch under a door | Insects and spiders 4 | A door sweep or weatherstrip is enough; rodents cannot fit |
| 1/4 inch around a pipe | House mice 12 | Use chew-proof steel wool or wire with caulk, not foam alone 12 |
| 3/8 inch wide crack | House mice can pass openings this wide 2 | Seal with metal or concrete 2 |
| 1/2 inch under a door | Young rats 3 | Fit the door tightly and seal the threshold 3 |
| Larger hole at a vent | Rats and mice 3 | Galvanized cloth or expanded metal with 1/2-inch mesh 3 |
Illinois Extension suggests a practical test: lie on the floor with the lights off, and if you can see daylight under a door, insects can get in 4.
For rodents, the pencil test works, because a mouse can pass any hole a pencil fits through 1. Our rodent exclusion planner lists the materials for each gap.
Where entry points show up on paperwork
On a pest inspection report, entry points are often marked on a sketch of the house or listed with photos. It should give the location, the size of the gap and the recommended fix, because a report that says only “seal entry points” without saying where is hard to act on.
On a rodent control quote, exclusion work is often a separate line from trapping, and it may list the number of openings, the materials (steel mesh, sheet metal, concrete) and whether the work is guaranteed. Our rodent control service page explains how trapping and sealing fit together.
On a termite or wood-destroying organism inspection, the language changes, because inspectors note wood touching soil and conditions that give termites a path, not just holes.
Why sealing entry points pays off
Benefits
- It stops pests before they arrive, so fewer pesticides are needed inside.
- A metal or concrete seal keeps working for years without reapplication.
- Sealing for pests also blocks drafts, which helps comfort.
- It works against many pests at once: the EPA lists screens, weatherstripping and caulk as basic prevention 5.
Trade-offs
- Finding every gap takes time, especially high openings used by roof rats 3.
- Sealing a home with pests still inside can trap them, so removal comes first or at the same time.
- Some small insects pass through standard window screen; closing windows during their season is the only sure block 4.
- Pests also arrive in packages, firewood and used furniture, which no seal can stop 5.
What sealing cannot do
No house is perfectly sealed, because homes need vents for air, drains for water and doors that open. The goal is to make openings too small for the pest you face, not to make the shell airtight.
Sealing also cannot stop pests that come in with people or with the things they carry. Bed bugs ride in luggage, cockroaches in grocery boxes and pantry pests in birdseed and dry goods 4. For those pests, checking items at the door matters more than any caulk.
The wrong material also fails fast. UC IPM says plastic screening, rubber, vinyl, foam and wood will not stop mice 2, and rats chew caulk and foam too 3.
What drives the cost of sealing entry points
We do not list prices, because they vary too much by home and region to state fairly, but the cost drivers are clear.
The number and height of openings matter most, because ground-level gaps are quick, while roof-line gaps need ladders or lifts and take longer. Material comes next, since sheet metal and concrete cost more than a door sweep but last longer against rodents. Access matters too, since crawl spaces and finished basements add labor.
Some companies include exclusion in a rodent plan; others price it as separate work with its own guarantee. Ask what is warranted and for how long, and read the cost guide to see how quotes are built.
Lifespan depends on material. Metal and concrete seals last as long as the surface they are attached to, but door sweeps and weatherstripping wear out with use and need checking.
How entry points are found and sealed
A professional exclusion job follows these steps. No permit is usually needed, but work on gas lines, electrical service or chimneys may involve other trades.
- Walk the outside. Start outdoors and check the roof line, eaves, soffits, vents, siding, foundation line and every utility entry 1.
- Walk the inside. Then move indoors and check under sinks, behind appliances, closets, attic, basement and crawl space 1.
- Look for signs. Grease rub marks, droppings, gnawing and daylight are the clues that show which gaps pests are actively using.
- Remove pests first. Trap or treat the pests already inside before closing their exits, so they are not sealed into the walls.
- Seal by size and pest. Steel wool with caulk or foam for small rodent holes; metal, cement or hardware cloth for larger ones 1, and caulk and sweeps for insect gaps 4. See caulking for pest prevention and door sweeps.
- Trim the edge. Prune limbs away from the roof and pull plants and mulch back from walls 35.
- Check again. Recheck every seal after a few weeks and look for new gnawing or droppings that point to a missed gap.
Stay safe at heights and around wildlife
Roof-line work needs proper ladders or a professional crew. Do not seal openings where bats or other wildlife may be inside; trapping animals in walls is cruel and can be illegal. If roof rats use overhead utility wires, UC IPM advises calling a pest professional or the utility company 3.
Keeping entry points closed
- Check door sweeps and weatherstripping each fall; replace any that let light through 4.
- Look over every window screen each spring, before you open the windows for the season.
- After any new cable, satellite or plumbing work, check the new hole in the wall, because installers often leave it unsealed.
- Walk the foundation line twice a year for new cracks or gnaw marks.
- Keep shrubs, vines and mulch pulled back from walls; the EPA suggests at least 18 inches 5.
- Keep floor drain screens in place and drain traps full of water 56.
The light test
With the room dark, look for daylight around doors, pipes and vents. Illinois Extension notes a gap as small as 1/16 inch can let insects and spiders in 4.
Signs pests are getting in, and when to call
Call a licensed company if you notice:
- Droppings or gnaw marks near pipes, vents or the base of walls.
- Scratching in walls or the attic at night, which can mean rodents above ground level.
- Insects clustering on sunny walls and then showing up indoors in fall 4.
- Ant trails that lead back to a single crack or electrical outlet.
- Openings high on the roof line that you cannot safely reach with a ladder.
If you hear animals in the attic during spring or summer, it may be a nursing mother with young, so leave the hole open and call a wildlife professional.
Rules that can apply
Federal. No federal law sets how a home must be sealed against pests. The EPA’s Citizen’s Guide (August 2017) lists screens, weatherstripping and caulking as basic prevention steps 5.
State and local. Housing codes in many cities require rental units to have intact screens, sound walls and freedom from pests, but the wording varies by place. Check your local code or housing agency.
Wildlife law. Bats and some other animals have state protection, and several states set times of year when exclusion from roosts is not allowed. Our bat exclusion page covers this.
Licensing. Sealing alone does not need a pesticide license, but any company applying pesticides as part of the job must be licensed by the state. See how pest control licensing works.
Entry points vs harborage vs conducive conditions
| Term | What it means | Example | Fix |
|---|---|---|---|
| Entry point | An opening pests use to get inside | Gap around a dryer vent | Seal it (exclusion) |
| Harborage | A place pests hide and nest | Cardboard boxes in a garage | Remove clutter (sanitation) |
| Conducive condition | Anything that helps pests survive | A leak, open food, wood touching soil | Repair or change it |
| Food and water source | What pests eat and drink | Pet food left out overnight 1 | Store and clean up |
Inspection reports often mix these words, but the fixes differ, because entry points get sealed while harborage and food are removed through sanitation.
Myths about how pests get in
- Myth Spray foam keeps mice out.
- Reality UC IPM says foam, plastic, rubber, vinyl and wood will not stop mice; use metal or concrete 2.
- Myth A mouse needs a big hole.
- Reality A hole about 1/4 inch, the width of a pencil, is enough 1.
- Myth Chicken wire is good enough for vents.
- Reality UC IPM says rats pass through lightweight chicken wire; use galvanized 1/2-inch mesh 3.
- Myth Only ground-level gaps matter.
- Reality Roof rats and house mice climb, so roof vents and eaves count too 32.
- Myth Window screens stop every insect.
- Reality Some tiny insects pass through standard screen; Illinois Extension says closing windows is the only sure block when they are active 4.
How climate changes which entry points matter
The gaps are the same everywhere, but the season when they matter shifts with climate. In cold-winter states, Illinois Extension advises sealing in fall, as days shorten, because box elder bugs, lady beetles and stink bugs look for winter shelter on warm walls 4.
Where roof rats are common, high openings matter more, because UC IPM notes roof rats climb and their entry points take longer to find 3. Check the seasonal calendar for when pests in your region start moving.
When entry points matter to you, and what to do next
If you see a few insects in fall, do a light test and fix the door sweeps, screens and small cracks yourself before cold weather arrives. If you see droppings, hear scratching at night or find fresh gnaw marks, call a professional to remove the rodents and seal with metal or concrete.
When you get a quote, ask for a list of openings with locations, the material for each and how long the seal is guaranteed. Ask whether trapping comes first, too. Our guide to choosing a pest control company lists more questions, and the recurring pest control page explains how ongoing service checks seals over time.
Quick decision guide
If you only see insects and the gaps are small, use sweeps, caulk and screens. If you find rodent signs, remove the rodents and then seal with metal or concrete. For high or hard-to-reach gaps, or wildlife inside, call a pro.
Questions about Pest Entry Points
What are the most common pest entry points in a house?
The most common entry points are gaps under exterior doors, holes where pipes and wires pass through walls, foundation cracks, attic and crawl space vents, torn screens and gaps at eaves and soffits.
The CDC also lists dryer vents, floor drains and the line where the floor meets the wall. Packages and firewood bring pests in too.
How small a hole can a mouse get through?
A mouse can get through a hole about 1/4 inch across, roughly the width of a pencil, according to the CDC and UC IPM.
UC IPM adds that house mice can squeeze under gaps about 1/4 inch tall and through openings 3/8 inch wide. That is why all holes larger than 1/4 inch should be sealed.
How small a gap can insects get through?
Gaps as small as 1/16 inch can let insects and spiders in, according to University of Illinois Extension. That is about the thickness of a coin, and a simple test is to look for daylight under doors with the room dark; if light shows, add or replace a door sweep or weatherstripping.
What should I use to seal holes against rodents?
Use materials rodents cannot chew. The CDC suggests steel wool held in place with caulk or spray foam for small holes, and metal sheeting, cement, hardware cloth or lath screen for larger ones.
UC IPM recommends galvanized metal with 1/2-inch mesh over vents. Foam, plastic, rubber, vinyl and wood alone will not stop mice or rats.
Is spray foam good for keeping out mice?
Not on its own. UC IPM lists expanding foam among the materials that do not work for plugging mouse holes, and it says rats chew through foam and caulk as well.
Foam can hold steel wool in place, which is how the CDC suggests using it, but for a lasting seal against rodents you need metal or concrete.
When is the best time to seal entry points?
For insects, fall is best, before they look for winter shelter, according to Illinois Extension. For rodents, seal any time you find gaps, but remove the rodents already inside first. Avoid sealing roof-line holes in spring and summer without checking for wildlife, since a mother animal may have young inside.
Do I need to remove pests before sealing entry points?
Yes, in most cases. Sealing a home with rodents still inside can trap them in the walls, where they may die and smell or simply chew new holes, so professionals usually trap or treat at the same time as sealing, then recheck. Never seal openings where bats or other wildlife may be inside.
Can pests get in through drains?
Yes. Penn State Extension names floor drains as a way in for American and Oriental cockroaches, and it advises screens over floor drains and water in every drain trap. The EPA also suggests screening floor drains. Run water in rarely used drains now and then so the trap stays full.
How far should plants be from my house to keep pests out?
The EPA’s Citizen’s Guide suggests keeping vegetation, shrubs and wood mulch at least 18 inches from the house. UC IPM advises pruning dense plants at least 2 feet from buildings and trimming tree limbs away from the roof so rats cannot reach it. Remove vines like ivy from walls where possible.
Sources
- U.S. CDC, How to Seal Up to Prevent Rodents, retrieved .
- UC Statewide IPM Program, Pest Notes: House Mouse (Publication 7483), retrieved .
- UC Statewide IPM Program, Pest Notes: Rats (Publication 74106, updated June 2025), retrieved .
- University of Illinois Extension, Tips for keeping pests out of your home (2023), retrieved .
- U.S. EPA, Citizen’s Guide to Pest Control and Pesticide Safety (August 2017), retrieved .
- Penn State Extension, Common Urban Pests: Identification, Prevention, and Control, retrieved .
Expert review
Written by the HyrePest Research team. Not yet reviewed by an outside expert. We say so rather than imply a review that has not happened; see our editorial policy.
How the numbers were checked: Gap sizes, materials and inspection locations follow the CDC seal-up page, UC IPM Pest Notes on the house mouse and rats, and Illinois Extension.
Where UC IPM gives two different limb-clearance figures, the page does not state one. Plant clearance is from the EPA Citizen’s Guide. No prices or products are given.
Suggest a correction. We fix errors and say what changed.