How to Get Rid of Bats in Your Attic

Bats are the most common attic mammal in much of the eastern US, but the noises and droppings overlap with squirrels, raccoons, and roof rats. Bats are dawn/dusk-active (silent during the day, then a sudden whoosh at sunset). Bat guano looks like mouse droppings but crumbles to dust between your fingers and contains iridescent insect-wing fragments. Squirrel droppings are smooth and oblong. Raccoon droppings are tubular and large. If the noise is daytime chewing or scampering, it's not bats — switch to the squirrel or rat protocol.

From late May through early August in most of the US, female bats roost in attics and give birth to one or two flightless 'pups'. Sealing the entry during this window starves the pups inside, kills them in your walls, and violates state wildlife law (and federal Endangered Species Act in regions with northern long-eared or Indiana bats). You can still INSTALL one-way doors before pup season starts (typically April) or after it ends (early August in northern states, late August in the South). Your state DNR's bat-exclusion calendar is the authoritative source — every state publishes one.

Bats leave the attic at dusk to feed. 30 minutes before sunset on a warm night (>50°F), station yourself with a view of every roofline. Count bats per minute and note which gaps they emerge from — typical attics have 2–6 active exits even when only one is obvious. Repeat for two consecutive nights to confirm. You need every active exit on a map before you proceed; sealing the wrong one traps them.

Daytime inspection (full PPE — Tyvek suit, N95+, gloves, eye pro) to find guano piles and roosting concentration. Guano under a specific roof joist tells you which entry the colony uses most. Also look for urine staining on insulation. Take photos; don't disturb the bats. Note: never approach a bat that lands on the floor — that's a rabies-exposure presentation. If a bat is on the floor or has had contact with anyone, call your state health department immediately for rabies-testing protocol.

A bat exclusion device — a netted sleeve, tube, or check-valve — lets bats squeeze out at dusk but blocks them from getting back in. Install one over every active exit you mapped. Critically: DO NOT seal any other gap yet. Bats will find a second exit if one is sealed too early, and the new exit becomes the new permanent entry point. Leave the exclusion devices in place for 4–7 consecutive bat-flight nights (warm, no rain) before doing the final seal.

Every night >50°F and not raining counts as one 'flight night'. Bats may stay inside on cold or stormy nights; those don't count. After 4–7 consecutive flight nights with the exclusion device(s) in place, watch one final dusk: if you see no bats emerge for two consecutive dusks, the colony is out.

Once you've confirmed the colony is out, remove the exclusion devices and seal every gap on the building — the active exits, every gap you mapped in step 3, and every gap >3/8 inch found during a slow ladder inspection of the roofline. Bats fit through gaps the width of a pencil. Use stainless or galvanized hardware cloth + sealant for any gap larger than a quarter inch; use exterior caulk for finer gaps.

Bat guano accumulates over years and carries histoplasmosis spores. Light contamination (under a few square feet, less than ½-inch deep): wet down with a sprayer first to stop dust, scrape into heavy-duty bags, bag and trash, then vacuum with a true HEPA vacuum (not a shop-vac with a HEPA filter — those leak). Heavy contamination (deep piles, soaked insulation, structural damage): hire a remediation pro. Always wear P100 + Tyvek; never sweep guano dry.

Insulation under a roost is saturated with urine and embedded guano — it can't be salvaged, and the smell will keep drawing bats back next season. Bag and remove all soaked insulation in the affected bays. Replace with fresh fiberglass or blown cellulose to the original R-value. Use this opportunity to add baffles and improve attic ventilation, which discourages future roosting.

Bats are insectivores — a single bat eats up to 1,000 mosquitoes a night. Excluding them from your attic and giving them a bat house 15 ft away keeps the local insect-eating population alive while keeping your house bat-free. Mount on a pole (not a tree), 12–15 ft up, with morning sun exposure, painted dark to hold heat. Best installed in winter or early spring before colony returns.

Each October, after pup season but before bats hibernate, walk the building with binoculars looking for new gaps: settled flashing, popped soffit panels, shrunk caulk lines, new gutter pulls. Seal anything you find. A 30-minute annual ladder lap is what separates 'fixed once' from 'recurring problem'. Save the exclusion-device kit — if a bat finds a new way in, you already have the tools.