In much of Southern California, the rat found in an attic isn’t the same kind that burrows beneath garages. It is the roof rat (Rattus rattus), a lean, long-tailed climber that prefers elevated spaces. Fruit trees, palms, ivy-covered walls, and overhead utility lines give roof rats easy routes onto houses. Small gaps around the roof can provide access to the attic.
Getting rid of the rats is a pest control job. Keeping them out and repairing the damage may also require roofing work. This guide covers both parts: where roof rats get in, what they leave behind, and the order in which to deal with it so the problem does not come back with the first winter storm.
Why roof rats end up in the attic
University of California Integrated Pest Management (UC IPM) guidance describes roof rats as nesting in “enclosed and elevated spaces, such as attics, wall voids, ceiling voids, and cabinets,” and outdoors in trees, shrubs, and dense vegetation such as ivy. They travel along fence tops and overhead utility lines, using their tails for balance, and they will range 300 feet or more for food. A citrus tree or an overgrown hedge next door can attract roof rats that nest in your attic.
An attic gives them what they want: shelter from heat and rain, insulation to shred into nests, and quiet. Once rats have nested in a space, UC IPM notes, the site keeps drawing them back unless it is cleaned out and closed off.
The roof entry points that matter most
Rats need very little room. UC IPM advises sealing every hole larger than 1/4 inch to keep out both rats and mice. On a typical Southern California house, these are the places to check first:
- Attic and gable vents. Screens tear, rust through, or were never meant to stop rodents. UC IPM recommends vent covers made of 1/2-inch mesh in 16- or 18-gauge galvanized wire cloth or expanded metal, and warns against lightweight chicken wire, which rats pass through.
- The eaves of tile roofs. Barrel and S-tile roofs leave a curved opening at the bottom of every row of tile. That opening is usually sealed with a metal or mortar closure, often called a bird stop.If the closure is missing or broken, rats can get beneath the tiles and may find a way into the attic.
- Fascia and the roof edge. Where a fascia board has rotted, or the metal edge flashing has pulled away from it, rats can gnaw a gap into the eave and work their way inside.
- Roof-to-wall joints. Second-story walls, chimneys and dormers meet the roof at flashing joints that open up as the sealant dries out and shrinks.
- Plumbing vents and chimneys. UC IPM recommends screening the tops of plumbing vent pipes more than 2 inches in diameter and fitting chimneys with a spark arrester.
- Rooftop solar panels.The space beneath an array can shelter pigeons and rodents.Nests and droppings can accumulate out of sight, near the wiring beneath the panels.
- Openings for wires and lines. Cable, satellite and air-conditioning lines often enter the house through holes much larger than the line itself.
Then look at the bridges. Tree limbs, ivy, and vines give rats a path onto the roof. UC IPM calls for removing overhanging limbs within 6 feet of the roof (its quick-tips sheet uses 3 feet as the minimum) and for thinning or removing climbing plants such as ivy, star jasmine and honeysuckle on the house.
Signs of roof rats above the ceiling
Roof rats are most active at night, so the first clue is often a sound: scratching or running in the attic or a drop ceiling after dark. In the attic itself, look for:
- Greasy smudge marks where fur rubs along rafters, beams and pipes.
- Shredded or tunneled insulation used as nest material.
- Gnawed wiring. UC IPM notes that roof rats chew the insulation on wires and can cause electrical sparks and fires in attics.
- Tooth marks on wood about 1/6 inch wide, larger than a mouse’s.
- Droppings near nests and along the routes the rats travel.
Outside, watch at dusk for rats moving along fence tops and utility lines, and check fruit and nuts in the yard for gnawing.
Get the order right: remove, seal, then repair
One mistake is sealing entry points while rats are still inside. Trapped animals chew new exits, often through the repairs that were just made, or die in the attic. A better sequence:
- Remove the rats. A licensed pest control operator can trap and remove them and confirm that activity has stopped.
- Seal entry points with materials rats cannot chew.Rats gnaw through plastic, foam, wood, and caulk. UC IPM recommends steel wool, wire screen and sheet metal for closing openings.
- Clean the attic. Contaminated insulation and nesting material are usually removed and replaced.
- Repair the roof. Chewed vents, displaced tiles and damaged edges are covered in the next section.
One Southern California detail: if the house is in a mapped Fire Hazard Severity Zone, replacement attic vents also have to meet the state’s wildfire building rules. Section 504.10 of the 2025 California Wildland-Urban Interface Code calls for vents covered with noncombustible, corrosion-resistant mesh with openings between 1/16 and 1/8 inch, or vents tested to the ASTM E2886 ember standard. That mesh is much finer than the 1/2-inch screen recommended for rats, so a compliant ember-resistant vent handles both problems. The Office of the State Fire Marshal publishes fire hazard maps that can be searched by address.
When rat damage turns into a roof leak
Rats usually don’t chew directly through intact roofing materials. The leaks they cause usually show up months later, when the rain arrives:
- Chewed vent boots and caps. Rubber pipe boots and plastic vent caps are easy to gnaw. Once torn, they let water run down the pipe and into the attic.
- Displaced tiles and torn underlayment. Rats and birds nesting under tile push pieces out of position and tear the underlayment, the layer that actually keeps water out on a tile roof.
- Clogged valleys and gutters. Nesting material, droppings and debris collect in valleys, gutters and roof drains, where they hold water against the roof instead of letting it drain away.
- Damaged edges. Gnawed fascia and loose edge metal let wind-driven rain into the eave.
Timing matters. In Downtown Los Angeles, about 12.4 of the 14.25 inches of rain in a normal year falls between November and March, according to NOAA climate normals. A rat problem found in summer leaves time to repair the roof before the rainy season. If you discover roof damage in December, it may need prompt attention.
If water is already coming through a ceiling, deal with the roof first. A contractor that handles emergency roof leak repair in Los Angeles can find where the water is getting in, cover the opening, and repair the damaged vent, flashing or underlayment while a pest control professional addresses the infestation. Ask for photos of what they find on the roof. They show the damage, and they help the pest control company confirm where the rats were entering.
A fall checklist for Southern California homeowners
- Trim tree limbs back from the roof, and cut ivy and vines off the walls.
- Walk around the house and look at the vents, eaves and roof edge from the ground. Binoculars help.
- On tile roofs, check that the bottom row of tile is closed off at the eaves.
- Check the attic for rub marks, droppings and disturbed insulation.
- Clear valleys, gutters, and roof drains before the first storm.
- Look under any solar array for nesting material.
- If you find damage, have the roof repaired before the rainy season rather than during it.
Roof rats are persistent, but they are opportunists. A roof with sealed openings, no overhanging branches, and fewer nesting spots beneath panels or tiles is harder for rats to access. Treat rat removal, entry-point sealing, attic cleanup, and roof repair as separate steps, in that order. Doing each one properly gives rats fewer chances to return during the winter.
References
- UC Statewide IPM Program, Pest Notes: Rats, UC ANR Publication 74106 (N.M. Quinn), updated June 2025. ipm.ucanr.edu/PMG/PESTNOTES/pn74106.html
- 2025 California Wildland-Urban Interface Code (Title 24, Part 7), Section 504.10, vents. Summary: Town of Paradise, “WUI venting requirements” (2025 code).
- NOAA NCEI 1991-2020 climate normals for Downtown Los Angeles, via Los Angeles Almanac (laalmanac.com/weather/we02a.php).
- Office of the State Fire Marshal, Fire Hazard Severity Zones maps (osfm.fire.ca.gov).
