Rats in the Attic: Signs, Risks and What to Do

Signs of rats in the attic

Look through the attic hatch with a strong flashlight. Signs include:

• Droppings along joists, on top of ducts and near the eaves
• Runways: flattened paths and tunnels through the insulation
• Nests of shredded insulation, paper or fabric in corners or near the eaves
• Gnawed wires, flex duct jackets and wood
• Dark rub marks on beams and rafters where rats squeeze past
• A sharp ammonia smell from urine

Sounds are the other clue. The county says rats are most active at night, so the noise usually starts after dark and is loudest in the late evening and before dawn.

How rats get into San Diego attics

San Diego roofs have a few weak points that come up again and again:

• Barrel tile roofs without bird stops, which leave open tile ends at the eaves
• Gable vents and soffit vents with torn or rusted screens
• Gaps where a second-story wall meets a lower roof
• Dead valleys and joints between old and new rooflines on homes with additions
• Gaps around solar conduit and AC line sets that pass through the roof
• Shrunken fascia boards on 1950s and 1960s ranch homes

Branches, palms and vines that touch the roof make all of these easy to reach. The county advises trimming vegetation at least 4 feet from the roof.

The damage they cause

The county notes that rats can cause structural damage or house fires by gnawing on walls and electrical wires. In attics they also:

• Soil and flatten insulation, which cuts its insulating value
• Chew through flex HVAC ducts, so the AC cools the attic instead of the house
• Leave urine stains that can show through ceilings
• Bring fleas and mites, which can move into the living space

If you see chewed wiring with bare copper, have an electrician check it.

How to get them out

The order matters:

• Trim branches and vegetation back from the roof
• Find and seal most entry points, leaving the main active one open
• Set snap traps along the runways in the attic, with the trigger facing the path
• Check traps daily and remove catches with gloves and disinfectant
• When catches stop for about a week, seal the last opening
• Watch for fresh droppings on the cleaned area to confirm they are gone

Sealing everything at once can trap rats inside, where they chew new holes or die in the attic. Avoid poison bait in the attic. Under AB 1788 and AB 2552, most anticoagulant baits can no longer be used at homes in California, and a poisoned rat that dies in the insulation is hard to find. See how to get rid of roof rats.

Cleaning the attic afterward

Once the rats are gone and the house is sealed, clean up. The CDC says not to sweep or vacuum droppings or nesting with a regular vacuum. Small areas can be wetted with a bleach solution of 1 part bleach to 9 parts water, soaked 5 minutes and wiped up with gloves on. A heavily soiled attic usually needs a crew with respirators and an insulation vacuum, plus new insulation. See attic and crawl space cleanup.

When to call for help

Call a provider if you cannot reach the roof safely, if the attic is too tight to move through, if you find chewed wiring or ducts, or if catches keep coming after two weeks. Ask for a written list of entry points and separate prices for sealing, trapping and cleanup. See rat control.

What to do tonight

If you hear rats overhead tonight, you do not need to go into the attic in the dark. Make sure the attic hatch is closed tight and that there are no gaps around it, recessed lights or the attic fan where a rat could drop into the house. Close the doors to bedrooms if the sound is above them. Put pet food and fruit bowls away. Then, in daylight, look outside for branches touching the roof and check the roof edge from the ground for missing bird stops or torn vents. Write down where the sounds were loudest. That is where the runway and nest probably are, and where traps should go first.