If the droppings you found are closer to the size of a raisin than a grain of rice, you're almost certainly looking at rat feces in the attic, not mice. That difference matters. Rats leave more waste per animal, they soak their runways with urine, and they chew through things mice can't.
Confirm it's rats, keep bare hands and faces well away from the droppings and urine, and deal with the rats and their entry points before anything else. Then the visible waste gets wet-cleaned and any insulation they've nested in or soaked comes out. How much that is depends on what the runways look like.
Rat droppings are big enough to measure against a coin
Rat droppings run roughly 1/2 to 3/4 inch long, several times the size of a mouse dropping. The shape tells you which rat you probably have:
|
Roof rat |
Norway rat
|
|
|---|---|---|
|
Dropping size |
About 1/2 inch |
Up to about 3/4 inch |
|
Dropping shape |
Slender, pointed at the ends |
Thicker, capsule-shaped with blunt ends |
|
Where it lives |
A climber: attics, roof voids, trees, upper walls |
A burrower: crawl spaces, basements, ground level, though it climbs |
|
How it reaches the attic |
Tree limbs, power lines, roof edges and vents |
Up wall voids and plumbing chases from below |
In practice, roof rats are the rodent most crews expect to find in an attic, especially in warmer and coastal regions. Norway rats do turn up, usually because they've climbed through the structure from a crawl space, which means the entry point you're looking for may be at ground level.
Freshness tells you whether the colony is still active. Fresh droppings are dark, shiny and soft. Older ones turn dull, gray and crumbly. A mix of both usually means ongoing activity.
Where rats leave their mark, and what else to look for
Rats are creatures of habit. They run the same routes every night, usually along an edge: the top plates where the roof meets the walls, along rafters and purlins, and the path between their entry point and their nest. Droppings concentrate along those runways and around the nest.
Look for the other signs too:
- Rub marks. Dark, greasy smears on framing where their bodies brush the same spot night after night.
- Gnawing. Rats chew constantly to keep their teeth in check, and wiring, duct jackets, PVC and framing are all fair game. Have an electrician look at any chewed wiring before the attic is closed up again.
- Flattened runways. Insulation along the eaves compressed into a trench, often stained yellow.
- Food caches. Pet food, nuts, fruit pits or birdseed stashed near the nest.
- Noise. Scratching and scurrying at night, often right after dark.
Rat urine is the bigger health concern
Droppings get the attention, but on rat jobs the urine is often the bigger problem. Rats urinate along their runways, and that urine soaks into insulation and framing.
Leptospirosis is the disease most associated with it. According to DC Health's leptospirosis fact sheet, it spreads through direct contact with the urine of infected animals, occasionally through food contaminated with infected rat urine, and occasionally by breathing in sprays of contaminated fluid. That's a strong argument for gloves, eye protection and covered skin, and for never pressure-spraying a urine-soaked area.
Hantavirus comes up on every rat job, and the details are more specific than most people think. The CDC's hantavirus risk-reduction recommendations tie the serious US form of the disease to native wild rodents such as the deer mouse, cotton rat and rice rat, rather than to the roof and Norway rats that usually move into attics. Norway rats can carry a related virus, Seoul virus, which has turned up in rats in the US, although the same report notes that human illness from it is largely confined to Asia. Nobody can tell which rodent left a pile of droppings, or whether it was infected, so the same wet-cleanup precautions apply in every rat attic.
Rats make a bigger mess than mice, and the insulation shows it
A rat colony concentrates its damage. Instead of fine tunnels through loose fill, you get packed, urine-stained runways along the eaves, large nests of shredded insulation and debris, and heavy droppings around both. That pattern shapes the removal decision:
- Droppings on the surface of clean insulation can be wet-cleaned and picked up.
- Runways and nest areas almost always have to come out, because urine has soaked down through the material.
- Activity across the whole attic, or a smell of urine at the hatch, usually means a full strip-out.
The CDC's rodent cleanup guidance sets the ground rules for the visible waste: never sweep or vacuum droppings or urine dry, soak them with disinfectant or a fresh bleach solution and let it sit, pick them up wet with paper towels, and double-bag dead rats and nests. Insulation contaminated with urine and droppings gets bagged and removed.
What changes on the removal day for a rat job
Rat jobs are heavier than they look. Insulation from urine-soaked runways is damp and dense, so a bag hits its weight limit well before it looks full. For that material we recommend our PRO-450 Super Duty bag: it carries our highest weight rating for a 75 cubic foot bag at 450 pounds and has the lowest dust of anything we make. Fill it lighter than you would with dry insulation, and swap bags as soon as one starts to go tight. On whole-attic jobs with lighter, drier material, the rest of our insulation vacuum bag range gives you options by fabric and size.
Dress for contamination, not for a clean retrofit. Our Microvek microporous coveralls provide a barrier against hazardous dusts and light liquid splash, which matters when you're kneeling on wet, stained runways. Bag them with the job waste when you're done.
And make sure the rats are actually gone before the first bag fills. Cleaning while the colony is active just gives them fresh insulation to nest in.
Order the bags before you pull the first runway
Contaminated rat jobs nearly always need more bags than a clean attic of the same size, because packed and damp material bulks up. Set the condition to packed or wet in our free bag calculator when you size the order, then call us at 404-354-6268 (we answer 24/7) if you want to check your order. RAM ships every US order free, the same day.
Frequently Asked Questions
How can you tell if rat droppings are fresh?
Fresh droppings are dark, glossy and slightly soft, while older ones are dull, gray and crumble when touched with a tool. A useful check after trapping is to wet-clean one section of the runway and look again a few days later; new droppings on the cleaned patch mean rats are still using it.
Do rat droppings in the attic mean rats are in the walls too?
Often, yes. Rats travel between floors through wall voids, plumbing chases and gaps around pipes, especially Norway rats coming up from a crawl space. If droppings are concentrated near the top of an interior wall, the route probably runs straight down through it.
Is it safe to leave old rat droppings if the rats are gone?
No. Old, dried droppings are exactly the material that turns into dust when someone later works in the attic, and urine-soaked insulation keeps smelling for as long as it's there. Cleaning up after exclusion is part of finishing the job.
Can rat feces in the attic be cleaned with a household vacuum?
Don't use any vacuum on loose droppings. The CDC warns that vacuuming or sweeping rodent waste can put contaminated particles into the air. Wet the droppings with disinfectant, let it soak, and pick them up with paper towels. Insulation removal vacuums are for extracting the insulation itself, after the visible waste has been dealt with.
Do roof rats and Norway rats need different cleanups?
The cleanup is the same, but the follow-up differs. Roof rats usually come in high, so exclusion focuses on the roofline, vents and overhanging branches. Norway rats tend to climb up from below, so the crawl space and foundation need checking before the attic is reinsulated.