The short version
Seattle rodent problems run all twelve months because winter lows near 37F never freeze the population out. The fix is exclusion: close every opening a quarter inch or larger with metal, then trap out what is already inside. Roof rats work Puget Sound attics from above and Norway rats work damp crawl spaces from below, so both ends of the building need attention.
- A quarter-inch hole is a rat entry, and rats chew it larger from there.
- Seattle's 38 inches of rain keeps crawl spaces damp and rodents supplied with water.
- Roof rats nest in attics across Puget Sound; Norway rats stay at ground level.
- Washington does not regulate Old World rats, so trapping needs no permit.
- Deer mice statewide make dropping cleanup a ventilate-and-wet job, never a sweep.
Written for homeowners in single-family houses with crawl spaces or attics, renters in older converted buildings, and anyone managing a small commercial space with a back alley. If you are hearing activity overhead, finding droppings in a garage, or seeing something move along a fence at dusk, this will help you work out what is happening and who should handle which part.
What to look for
Four rodents appear in Washington's state data for Seattle: Norway rats, roof rats, house mice and deer mice. The two rats split the building. Roof rats are the climbers, and the state data places them in Puget Sound attics specifically, arriving over fences, wires, hedges and branches, then entering through a gnawed vent screen or a soffit gap. Norway rats stay on the ground, digging burrows in soft, wet soil against foundations and under sheds and decks. The local advantage they all share is water. With average humidity near 73 percent and rain spread across most of the year, a Seattle crawl space stays damp, and a damp crawl space is shelter and drinking water in the same place. Damp wood is also easier to gnaw, and rat incisors grow about five inches a year, so chewing is not an occasional behavior but a daily requirement. That combination is why a quarter-inch gap does not stay a quarter inch for long.
- 1Running or scratching overhead at night, tracking the same line across a ceiling.
- 2Blunt-ended droppings about half an inch long on a crawl space vapor barrier or garage shelf.
- 3Small pointed droppings in a drawer or behind the refrigerator, meaning mice not rats.
- 4Half-inch footprints or tail drags in dust on a crawl space floor.
- 5Chewed corners on a vent screen, soffit board or the bottom of a garage door.
- 6Fresh burrow openings in the soil next to a foundation, deck or shed.
- 7Flattened, hollowed insulation in an attic bay or under a floor, pulled apart for nesting.
Why it’s worth acting soon
- A pair in a crawl space in September can be a colony by spring, given rat litters of six to ten.
- Chewed wiring under a floor or above a ceiling is a fire risk nobody spots until it fails.
- The CDC lists leptospirosis, rat-bite fever, salmonellosis and tularemia among illnesses rodents spread directly.
- Wet insulation shredded for nests stops working, and heating a Seattle winter gets more expensive.
- Every extra month means more chewed openings, which makes the eventual sealing job bigger.
Treatment options and typical costs
Structural exclusion in metal
Quoted after inspection
Hardware cloth over foundation and attic vents, sheet metal on gnawed corners, proper flashing where a deck or addition meets the wall, and steel wool packed behind sealant at pipe entries. Where a Seattle house sits over a vented crawl space, much of this work happens below the floor and around the perimeter.
- Time
- Set by the number of openings the inspection finds
- Best for
- Any building that has had rodents more than once
Trapping with follow-up counts
Quoted after inspection
Snap traps placed on established runways in the attic, crawl space and interior, then checked until nothing is caught for a full cycle. The catch record tells you where the traffic is and whether the sealing worked, which no bait station can do. Expect several weeks rather than a single visit.
- Time
- Several visits, until a full cycle passes with no catches
- Best for
- Clearing the animals already living in the structure
Crawl space cleanout and vapor barrier repair
Quoted after inspection
Where rodents have been under the floor for a while, contaminated insulation and torn vapor barrier come out, the space is wet-cleaned rather than swept, and new material goes back once entries are closed. Doing this before sealing wastes the money, so ask about the order of operations.
- Time
- Depends on the size of the crawl space and the damage
- Best for
- Heavy droppings or fallen insulation under the floor
Access reduction around the building
Quoted after inspection
Cutting laurel, ivy and branches back from the roof, lifting stored wood off the ground, and securing bins takes away the ladders and the food. Wherever plantings touch the eaves, this is the difference between a roof rat reaching the roofline and not.
- Time
- One visit, repeated yearly
- Best for
- Properties with hedges or trees close to the house
Prices are typical published ranges. Ask what’s included before you compare quotes.
Bathroom vanities hide the same plumbing gaps as the kitchen. A quick look with a flashlight shows droppings or rub marks long before you see a mouse.The crawl space is usually the whole story.
From a Norway rat's point of view there is no better address on the block. Getting in is easy because crawl space vents are the weakest part of most foundations. Original screens rust, get bent by a lawnmower or simply have a quarter-inch mesh gap at one corner, and rats enlarge what they find. Once under the floor they follow plumbing and duct penetrations up into wall cavities, which is how a crawl space problem becomes a kitchen problem. What to do about it is unglamorous. Every vent gets covered in hardware cloth screwed and washered rather than stapled, every pipe and duct entry gets closed, the vapor barrier gets repaired, and drainage gets fixed so the space is not holding water. Then trapping clears what is left underneath, and the follow-up counts tell you whether the seal actually held. In a Seattle house with a crawl space, the rodent problem often lives in a space the owner has never entered. A vented crawl space under a heated floor is warm on top, sheltered from 38 inches of annual rain, and lined with fiberglass insulation that tears into perfect nesting material.
Roof rats in Puget Sound attics.
Hedges grown into the eaves, trees reaching over rooflines, utility lines, fences and ivy climbing a wall all work as ladders, and a roof rat will use any of them. At the top they look for the usual weak points: a gable vent with torn screening, a gap where two roof planes meet, a soffit corner that never got closed properly, a dryer or bath fan termination with a broken flap. None of these are visible from the ground, which is why a homeowner can seal a whole foundation and still hear running overhead. The access reduction matters as much as the metal. Cutting branches back several feet, stripping ivy off walls, and thinning hedges that touch the roof removes the route rather than the animal. Do the pruning first, because a rat that can no longer reach the eave has to find another building, and there is usually an easier one nearby. Washington's state data singles out Puget Sound attics as roof rat territory, and a look around a Seattle yard at dusk shows why.
A metal vent cover with a working flap keeps mice out all winter. Plastic flaps crack in the cold and get chewed open.A working calendar for a city with no freeze.
Fall brings the peak, and the pressure carries on through the wet months. Saturated soil pushes burrowing rats toward drier shelter under floors and into garages, and cold nights around 37F make a heated structure attractive without ever forcing a die-off outside. Spring is the discovery season. You open the shed that has been shut since October, or crawl under the house for the first time in months, and you find the droppings. That is the moment to remember the ventilate-and-wet cleanup routine rather than reaching for a broom, and to book the exclusion work while the weather still cooperates. Places with hard winters get one clean autumn spike. Seattle gets a long soft one, so the useful way to plan is around rain and daylight rather than temperature. Late summer and early fall are the repair window. The ground is at its driest, crawl spaces are workable, roofs are safe to walk, and pruning can happen before the wet arrives. This is when sealing should be done, and it is also when the outdoor population starts testing buildings ahead of the rain.
What a first visit should cover.
Then upward: eave and soffit gaps, gable and attic vents, exhaust terminations, and any hedge, limb or cable offering a route to the roof. You should end with a punch list of openings and the material proposed for each, a trap plan with placements and a return schedule, and a clear statement of what is not included. If the visit produces a monthly price and a couple of stations by the driveway, ask what part of the building it actually changes. A good first appointment is mostly inspection, and most of it happens in places you would not choose to go. Outside, expect a full circuit at grade: foundation vents, hose bibs, gas and electrical entries, garage and service door clearances, basement window frames, and the seams where a deck, porch or addition meets the original structure. Then the low space. Under the floor is where droppings, rub marks, footprints and shredded insulation show the actual routes, and where daylight through a gap is easy to spot from inside but invisible from the yard.
Renters, landlords and shared buildings.
If you rent, keep a record. Dated photos of droppings, notes on what time you hear activity and where, and a written request are far more effective than a phone call. Ask specifically for exclusion at the building envelope, meaning the crawl space vents, the foundation and the roofline, because that is the work a tenant cannot do and the work that ends the problem. If you own the building, the sequence saves money. Seal the shared envelope first, then trap unit by unit, then deal with the garbage and recycling area, which may be a shared enclosure that feeds the whole population. With median home values around 850,000 dollars in Seattle, the cost of hardware cloth is small next to chewed wiring, wet insulation and repeat service calls across several winters. In a converted house or a small apartment building, rodents move between units through the same crawl space, stair chase and plumbing runs that serve everyone, so a trap line in one unit usually redirects the traffic instead of ending it.
What affects the price
- Crawl space clearance and whether standing water or a torn barrier makes it slow going.
- How many foundation vents, hose bibs and utility penetrations need custom metal work.
- Whether roof rats are involved, which adds ladder work at the eaves and vents.
- Amount of contaminated insulation to be removed and replaced under the floor or overhead.
- Slope and access, since a house cut into a hillside is harder to work around than a flat lot.
- How many follow-up trap checks are included before the job is called finished.
📊
What's your biggest concern about rodents?
When to call for help
And call when steady trapping has not brought the numbers down, which almost always means an open route is replacing what you remove. Call if you find burrows outside, since Norway rats range well past your lot line. Get help when the crawl space is involved, because working in a damp, low space with contaminated insulation is unpleasant and needs proper protection. Get help when the sound is coming from above a ceiling, since roof rat entries are usually at height and finding them means a ladder and an attic crawl.
What you can do yourself
Set snap traps flush against a wall where you see droppings, check them daily, and a small kitchen mouse problem often resolves without outside help. Washington does not regulate Old World rats, so nothing stands between you and a trap line on your own property. Cleanup is also a homeowner job if you follow the rule: ventilate thirty minutes, wet with bleach solution, wait five minutes, wipe with paper towels, and never reach for a broom or a vacuum. Deer mice live throughout Washington and the state health department ties them to one to five hantavirus cases a year, so this is worth doing properly in a shed or garage. What is worth paying for is the sealing, especially anything under the floor or above a ceiling. Those are the spaces where entries hide and where a partial job leaves the route open. Trapping is fair game for a homeowner and often works.
Rodents in Seattle
Summer highs around 76 degrees and a winter that only drops to about 37F mean the outdoor population never crashes, which is why Washington's state data treats rat activity here as a year-round matter rather than a season. The state has also made the legal picture simple: Old World rats are unregulated, and killing them is unrestricted, so nothing delays a homeowner acting quickly. The animal that changes the safety math is the deer mouse, which lives throughout Washington and carries hantavirus. Seattle sits at about 175 feet of elevation in a Marine West Coast climate, and for its 749,000 residents the building detail that matters most is often what lies under the floor. A house over a vented crawl space gives Norway rats warm, dry shelter directly under a heated floor while the yard outside takes 38 inches of rain a year.
Local research
Rodents in Seattle, WA: what the public record shows
Before you compare quotes, it helps to know which rodents actually live in Washington, when they are busiest around Seattle, and what the state figures look like. Everything below links to the agency or university page it came from.
Rat litter size
Old World rats are not regulated; killing is unrestricted.
WDFWRat entry hole
Footprint about 1/2 inch long; incisors grow 5 inches a year.
WDFWRodent species recorded in Washington
- House mouse (Mus musculus) — Enters at 1/4 inch; 5-10 litters per year; eats about 200 small meals a night.
- Norway rat (Rattus norvegicus) — Burrowing rat of basements, sewers and ground floors; tail shorter than head plus body.
- Roof rat (Rattus rattus) — Climber of attics and trees in warm and coastal regions; tail longer than head plus body.
- Deer mouse (Peromyscus maniculatus) — Primary U.S. hantavirus carrier; lives throughout Washington and the interior West.
When rodents are busiest around Seattle
Year-round; roof rats in Puget Sound attics.
Rules that apply in Washington
For context, nationally
- 1/4 inch (the width of a pencil) — Smallest gap a mouse can enter. CDC
- 890; 35% fatal; 94% west of the Mississippi — Hantavirus cases reported since 1993 (through 2023). CDC
Sources: Hantavirus; WDFW; CDC; Pest Notes: House Mouse; Pest Notes: Rats. Figures are quoted as the source prints them. How we check our sources
Simple ways to keep rodents away
- Cover every foundation vent with quarter-inch hardware cloth and check the screens each fall.
- Cut hedges and branches back several feet from the roof so roof rats lose the bridge.
- Fix crawl space drainage; standing water in a wet Seattle winter is a rodent water supply.
- Fit a proper sweep on the garage door so no half-inch gap remains at the bottom corners.
- Store firewood off the ground and away from the wall, not stacked against the siding.
- Screen dryer and bath exhaust terminations, which are common overlooked openings at the eave.
- Keep bird feeders away from the house or take them down when you see droppings.
- Walk the perimeter in September, before the fall push, and again in spring.
Before you call, sketch where you have seen droppings or heard noise and measure any gaps you found. It makes the first visit faster and the quotes comparable.Did you know?
A rat's footprint runs about half an inch long, which makes tracks in crawl space dust easy to read.
The CDC has recorded 890 hantavirus cases since 1993, and 94 percent of them occurred west of the Mississippi.
Rodents pass illness along indirectly as well, with plague, Lyme disease and murine typhus riding the fleas and ticks they carry.
Questions people ask
Why do Seattle houses get rats in the crawl space?
A vented Seattle crawl space sits under a heated floor, holds insulation that shreds into nesting material, and needs only one damaged vent screen to let rats in. Norway rats burrow in the soft wet soil outside, then move in through the gap they find at grade. If your house has one, the crawl space is often the driest warm place on the property in a city that takes 38 inches of rain.
How small an opening has to be sealed?
Rat incisors grow around five inches a year, so gnawing is constant. Use metal mesh, flashing or mortar, because foam alone gets chewed through. A quarter of an inch. Washington's wildlife agency describes that as the entry hole size for a rat, which then chews it larger, and the CDC uses the same quarter-inch figure for mice, comparing it to the width of a pencil.
Do I need a permit to kill rats in Washington?
You can set traps on your own property at any time of year. Pesticide products are a separate matter and are regulated regardless, so ask any provider what they intend to apply and where. No. WDFW states that Old World rats, meaning Norway rats and roof rats, are not regulated and that killing them is unrestricted.
Is it a rat or a squirrel above my ceiling?
Rat droppings are blunt-ended and about half an inch, and you will often find a greasy rub mark where they cross a rafter or top plate. WDFW notes rat footprints run about half an inch long. Timing separates them. Squirrels are active in daylight and quiet at night; roof rats start after dark and run into the small hours along a repeated route.
How fast does a rat problem grow here?
Washington's wildlife agency puts rat litters at six to ten young after roughly three weeks of gestation, with the young breeding themselves at three to four months. Seattle winter lows average 37F, so nothing thins the outdoor population between generations and a small autumn problem becomes a much bigger spring one. Fast, and without a winter pause.
How do I clean up droppings safely?
Glove up, spray the droppings with a bleach solution of about a cup and a half per gallon, let it soak five minutes, and wipe up with paper towels. The CDC is explicit about never sweeping or vacuuming, since both throw dried particles into the air where you are breathing them. Open the space and stay out of it for thirty minutes, then work wet.
Should I worry about hantavirus?
The Washington State Department of Health reports one to five cases a year and notes that about one in three people diagnosed have died, with infected deer mice living throughout the state. Exposure comes from disturbing droppings in a shed, cabin or garage that has been closed up, which is why the wet-cleanup rule exists. Take it seriously in outbuildings rather than the kitchen.
What should a quote actually list?
It should also state how many follow-up trap checks are included, whether crawl space or attic cleanup is in the price or extra, and what happens outdoors if there are burrows. A monthly bait-station price with no repair work in it is a subscription, not a solution. Specific openings and the material used to close each one, not a single line reading exclusion.
Nearby cities
Related guides
Sources (6)
The facts in this article come from the public sources listed above. Every home is different, so ask the company you talk to about pricing and what’s included. Published by Rodent Exterminator · Updated October 11, 2026 · How we write these guides