Raccoon outdoors on a downspout (C) Daniel FriedmanGuide to Keeping out Bats, Birds, Mice, Rats, Squirrels, Raccoons from your Building

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Animal entry points in buildings:

This article discusses how to find where animals are getting into your building and how to keep them out, including bats, birds, rats, mice, and squirrels and even raccoons. This article series focuses on removing pet or other animal odors from buildings due to pet urine, pet feces, wild animal urine, or even human urine on and around buildings or on clothing and other soft materials.

The little stuffed animals in this photo include a skunk - both were innocent of any pet-crimes, but they had been placed at either side of a basement door jamb to cover stains from basement water entry.

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Suggestions for Finding the Source of Animal Entry Points in buildings

Stuffed animals were hiding building damage (C) Daniel FriedmanArticle Contents

Watch out: in addition to their common role as allergens, animal feces, urine, even hair can offer serious health hazards including from various pathogens: bacteria, viruses, even possibly rabies.

Watch out: also for wild animal bites, bacterial and viral hazards when entering confined spaces where invaders are or have been present. The author (DF) became temporarily ill after (foolishly) working in a "clean looking" crawl space that later he realized had a heavy contamination of fecal and urine contaminated mouse dust. Bat and rodent droppings as well as bird droppings can be a source of a pathogen potentially dangerous to humans, the fungus Histoplasma capsulatum.

Watch out: before sealing up a hole in a soffit or wall where squirrels or bats are entering your building, make sure the animals are not going to be trapped inside where they will be mad, frightened, hostile, even dangerous (like a rabid raccoon), or ultimately dead and another source of stink.

Common Spots for Animal Entry in Buildings

  • Look outside too for Bats, Birds, Rodent Entry Points - if your building has been invaded by bats, rats, mice, squirrels, or other wild animals, you should inspect both indoors and outside for openings or stains and marks that indicate points of entry and exit for those creatures.

    Consult with a pest control professional who may have a practiced eye at spotting where animals are getting into your attic, roof, walls, basement, and who may be able to provide a repellant that will at least temporarily drive them out - alive.

    While there are no bat control poisons currently approved in the U.S., we have found that moth balls (naphtha) are an effective repellent for bats and squirrels, though naphtha odors are also repellent to some humans.

    And a small number of bats (less than 1% of bats are rabid according to the U.S. CDC) and unfortunately in some areas of the U.S. a larger number of raccoons may be carrying rabies. If you see an animal acting oddly, stumbling, or apparently unafraid of humans and very aggressive, stay away and don't get bitten.

    At BUILDING SAFETY HAZARDS GUIDE we discuss handling hazards from pets or other animals that may bite a building inspector.

    Bats in the Building? Our photos, below left and right (courtesy of Paul Galow), show how easy it may be to spot an outdoor point where bats were entering a building: bat droppings were noted on the ground, and stains are noted at the top of the wall just over that point.

  • A good time to seal building openings against bats is late fall when the young have matured and leave their roosts each evening - just make sure they are not at home before you seal a building entry point. Or try installing a "one-way" flap over the opening that will let the bats out but not back in. Leave that in place for a few days or a week, then close it permanently.

Stains from bats on a building wall (C) Daniel Friedman Droppings indicate bat activity at a building (C) Daniel Friedman

Here are two more bat-invasion photographs. You will see that the cupped metal roofing formed a nice opening for bats to enter this home, and again, a telltale collection of bat guano droppings below this very spot. Birds and squirrels also enter buildings at openings like this, as we discuss just below.

Watch out: do not kill bats unnecessarily. Bats are already in trouble in many areas of the world, including some of the 45 species found in the U.S. And we need them. Bats eat large numbers of night-flying insect pests (such as mosquitoes) and are an important part of our environment.

Watch out: Histoplasmosis (from bat droppings) is an infection caused by inhalation of Histoplasma capsulatum. In people with compromised immune system this can be a particularly dangerous infection, potentially fatal if not treated. See also granuloma, iritis, lung nodules. More information is

Entry point for bats at a building (C) Daniel Friedman Droppings indicate bat activity at a building (C) Daniel Friedman
  • Birds in the Roof Structure or attic may be entering through a hole they managed to peck in a roof overhang or soffit such as shown in our photo at below-left (courtesy of Paul Galow).
  • Birds in the Attic at infestation levels may be obvious if you spot bird dropping stains such as those shown on our photo (below-right).
Bird entry point into a roof overhang(C) Daniel Friedman Bird dropping stains on an attic beam  (C) Daniel Friedman

Watch out: Cryptococcus infection (cryptococcosis): (from bird droppings), at primary risk are people with compromised immune system but normal adults can also be infected by inhalation of Cryptococcus neoformans, leading to a form of meningial encephalitis. Cryptococcosis is a fungal disease caused by Cryptococcus neoformans or Cryptococcus gattii.

Most people do not get sick with cryptococcosis, but some people are more likely than others to get this disease. For these people, cryptococcosis can cause serious symptoms of lung, brain and spinal cord disease, such as headaches, fever, cough, shortness of breath, and night sweats. Cryptococcus neoformans is found in bird droppings. More information is

Dead mouse odor (C) Daniel Friedman
  • Also check for dead animals in building attics, crawl spaces, wall or ceiling cavities and in duct work or air handlers or chimneys.

    Animal odors in buildings can occur when an animal such as a mouse or rat has died in a building cavity.

    A dead animal smell has been described by our clients with a wide variety of terms ranging from a vague noxious stink that seemed to vary with humidity to a sweet sickly smell.

  • Dead animals or even insect nests in building plumbing, especially building vents, can also produce unexpected sewer odors - see Septic and Sewer gas odor links discussed below.

    Rodents, especially in the HVAC system such as air ducts, may also be a bacterial or Hanta virus hazard.

Are There Squirrels in the Attic?

Our photos below show a stunning nest project built by squirrels in the attic of a 1960's home in New York. The squirrels entered through openings in the home's aluminum soffit covering, tore up fiberglass insulation, and built the mounded nest in our photo at below left. Squirrel droppings on attic insulation are shown in our second photo, below-right.

Bird entry point into a roof overhang(C) Daniel Friedman Bird dropping stains on an attic beam  (C) Daniel Friedman

Below at left we show another sign of squirrel invasion of an attic: leaves brought into the attic to add to insulation as a nesting material.

One of our favorite squirrel invasion indicator photos provided by a reader is shown at below right. When squirrels nest or simply hide in an aluminum downspout, the sound or smell of the squirrel can be enough to drive some dogs mad as they try to tear their way into the squirrel's hiding place (below right).

Bird entry point into a roof overhang(C) Daniel Friedman Bird dropping stains on an attic beam  (C) Daniel Friedman

Advice for Keeping Mice and Rats and Squirrels and Raccoons out of Your Home

Skunk on the Vassar Golf Course (C) Daniel Friedman

Pest control experts recommend several simple steps that will discourage mice and squirrels from moving into your building as they are inclined to do particularly at the beginning of cold weather:

  • Housekeeping: clean up spilled food, seal food in rodent-proof containers
  • Garbage: garbage and trash cans should be made of metal and kept closed; clean up any spilled garbage around your trash cans both indoors and outside.

    Watch out: be sure your garbage can lids fit securely - raccoons are very good at opening them up to explore. And never corner a racoon indoors - you will be sorrier than the raccoon will be when you're bitten. (Not to mention the occasional rabies worry).

Our photo above shows a skunk rummaging on a golf course. If you see a skunk meandering in daylight stay well away - stay away any time for that matter. This skunk was found dead two days after its photo was taken, probably due to rabies. .

Open petfood invites mice and rats indoors (C) Daniel Friedman

  • Pet food: we found that storing open bags of cat or dog food invited mice into the same area, a problem solved by keeping those large pet food bats in a small metal covered garbage can. We also stopped leaving pet food in bowls overnight.
  • Seal Building openings: as we discussed above about bats, look outside for openings into the building such as at soffits or roof eaves, especially near overhanging or close tree branches (squirrel highways), and close to the ground look for openings into the basement at vents, windows, or building sill plates and siding bottom edges.

    Seal these when you won't be trapping animals inside. We have read that mice can enter a building through openings as small as 3/8"!.

Snow time means thinking too late about heating costs

Trim shrubs at least a foot away from the building walls; we prefer 18". This also reduces the attractiveness of the building to insect pests such as termites and carpenter ants.

If your home is in an area where Norway rats are a problem, keep low growing shrubs away from your building walls entirely as those rats burrow under them, especially Junipers and Taxus.


If your building odor complaint source is found to be outdoors, see URINE ODOR REMOVAL at BUILDING EXTERIOR.

Also see URINE ODOR REMOVAL in CLOTHING This article describes bacterial/enzyme based cleaners that may be extra effective in removing human or animal urine odors from clothing, diapers, bedding, towels, etc.


Raccoons in the Attic: A Christmas Story

Raccoon outdoors on a downspout (C) Daniel FriedmanThe following story is true, only Laura Waterman's name has not been mentioned.

Dan and Laura were snuggled up reading in bed on a cold Poughkeepsie January night. Suddenly overhead they heard

SMACK! rattle, rattle, rattle, rattle, rattle, rattle, roll. Something or someone was in the attic! Now they heard the sound of little clawed feet scampering across the attic floor just over their heads. The home, built in 1900, was a neo-Victorian with a large walk-up attic wherein were stored the usual detritus, old rugs, suitcases, trunks, broken lamps, bicycle parts, and other who-knows-what. Some animal, maybe more than one of them, was smashing something around in the attic. What the hey?

Dan tiptoes over to the door at the bottom of the attic stairs in his pajamas. He leans an ear against the cold red-varnished wood. Cold air leaks out of the attic and rolls across his bare toes adding to the chill of the sounds of intruders above.

SMACK! rattle, rattle, rattle, rattle, rattle, rattle, roll. More scurrying about, excitedly running to and fro across the wooden attic floor.

Trained in several forms of combat and three martial arts, Laura nevertheless cowers in their bedroom doorway.

"Don't open that door!" she advises in a voice quavering with emotion. "I'm telling you, for god's sake, don't open that door!"

Dan remembers having recently freed a real estate agent who'd been shut tight into the attic of another New York home by Dennis the Menace, the first and last child of her clients. Dennis slammed the attic door shut and ran downstairs, hopped into the family car, and Dad drove them away. The agent was later heard shouting out of a third floor window. "Soooomebody, Get me outa here!" It took some hammering, prying, and some gouging scarring of the door to get her out.

Dan grimaces in thought. He is glad that their attic door too can be difficult to open.

SMACK! rattle, rattle, rattle, rattle, rattle, rattle, roll. More scurrying. SMACK! rattle, rattle, rattle, rattle, rattle, roll. SMACK! rattle roll, roll, roll, smack rattle, roll.

Dan leans harder on the door to be sure it is latched tightly and inspects the lock.

"We'll check up there tomorrow when whatever it is has gone out for water" he concludes.

SMACK! rattle, rattle, roll, rattle, SMACK! rattle, rattle, rattle, roll, roll, roll. More scurrying, this time they hear nasty little feet scampering about, maliciously tearing paper, and gleefully rolling things about on the floor. Only the sounds of human giggling and laughter were missing.

By dawn the smacking, rattling, rolling and scampering had subsided. The intruders were asleep. Or they had gone out for breakfast at the convenient and always-open Poughkeepsie Diner dumpster. Dan knows about the dumpster because his dog Katie made a beeline for it whenever she ran away.

Laura waited. Dan waited. Mara was still sleeping in her own bedroom - they'd shut her door too.

After the humans had eaten their own breakfast (from the refrigerator not the dumpster) they took a walk around the house outside. Close inspection showed an open board on the under-side of the left rear roof soffit, lots of soot smudges, and a short leap-distance away, the huge old oak tree near the corner of the house.

They waited some more. Listening against the attic door: silence. Nobody really wanted to open the door but finally, carefully Dan and Laura ease open the door. Then, thinking some more, they close and go back to the kitchen where they gather their biggest pots and pans.

Throwing open the attic door and shouting "BEAT IT YOU BUMS" they bang the pots and pans together. BANG! CLANK!

The pans become lopsided, the pan handles bend and two pots are ruined. So is their hearing. Some neighbours are on the verge of calling the sheriff but they don't. But the attic is empty of intruders. Most likely the attic was already empty before Laura and Dan even started all that bang-clank foolishness.

Next they tiptoe up the attic stairs to see an amazing sight: there are sooty racoon footprints everywhere. Everywhere! The attic has been ransacked.

Scattered about the floor are two dozen bright, shiny green, red and gold Christmas ornaments that the raccoons have found irresistible. Ornaments are everywhere. A Christmas miracle, not one ornament has been broken broken. They're dirty, though. How could this be? The Christmas ornaments had been stored in a cardboard box that was itself at the bottom of a pile of other stored items. The raccoons had found the box, opened it, taken out the ornaments, and initiated a smack, rattle and rolling ornament festival on the attic floor.

Laura begins picking up the fragile blown glass bulbs, pyramids, Santa-Houses, stars, and whatnots. Together they replace the ornaments back into the compartmented box.

Thinking about the raccoons and that the soffit is still open to intruders, Dan opens a large chest, lifts out its contents (old wedding dress, towels with frayed edges and holes, bathing suits worn by his parents in 1939, shoes and a faded Confederate flag from Richmond). He places these aside. The box of ornaments is placed in the bottom of the chest and the chest is then re-filled with the rest of its contents. The heavy cover is closed. There's no lock.

After some sweeping-up they close the attic door and put a couple of bricks against it from outside.

"Tomorrow we'll borrow Art's 40-foot ladder and nail up that soffit", Dan offers. Laura smiles and looks doubtful. It's still cold outside. Mara, home from school passes the attic door and asks "Hey Dad, why are all those bricks leaning against the door"?

After a quiet dinner they read, then retire to read some more. (Any other possible activities that they might have pursued will not be discussed in this raccoon field report). Reading. Reading. There is no TV. They don't have a TV, but Mara's teachers don't believe that and accuse her of being sassy.

SMACK! rattle, rattle,rattle, rattle, rattle, roll !! Scurry, scurry, scurrying feet. SMACK! rattle, rattle, roll. SMACK! SMACK! SMACK! rattle, rattle, rattle, rattle, rattle, roll. More scurrying.

"You have to be kidding me!" Dan exclaims. He and Laura run barefoot out the back door to the barn. From there they carry all of the spare bricks from the barn back upstairs and pile them against the attic door. It takes four trips. Then they wait for morning.

The second morning they again enter the attic. More sooty footprints. The raccoons had not a moment's trouble sniffing out the box of ornaments where it had been hidden. They must have teamed up - surely it would have have taken at least two of them, maybe four, to open that old storage chest. Once opened by PROST, the Poughkeepsie raccoon ornament smacking team, the chest quickly yielded up its old wedding dress, towels with frayed edges and holes, bathing suits worn by his parents in 1939, shoes and the Confederate flag from Richmond - these have been tossed aside and the box of ornaments has again been taken out, opened, and its contents served-up to all four corners of the attic.

Again not one ornament has been broken. But this time one of the raccoons from Poughkeepsie has peed on the Confederate flag from Richmond.

The humans now understand. This event is going to continue until the raccoons get tired of it or until Dan nails new plywood onto the soffit.

Jewish people ought not to store Christmas decorations. What are they doing with them anyway?

Animal Feces & Urine Detection & Clean-Up

Reader Question: how do I clean up bat droppings & bat urine in our cabin?

We discovered a huge colony of bats living under the roof of our log cabin. I used a black-light (see UV LIGHT BLACK LIGHT USES) and found bat urine on all the main beams in the house as well as all the walls in the cabin. I have had restoration people tell me it could be cleaned and others said no all the wood is going to have to be replaced who is telling the truth? I have read that bat urine is 70% urea which would seem very strong. We believe they have been there for 6 years. - S.S. 8/12/12


It is nonsense to replace structurally sound wood because of bat urine or other surface contaminants. What makes sense to me is to clean the area thoroughly, including HEPA vacuuming and perhaps use of a sanitizer; when the wood surfaces have dried your remediator may want to apply a sealant to give maximum odor control - it's the same process used after a post-fire remediation in a building or after a mold cleanup. More about odor control in buildings that have been peed-on or in is

If there are wood beams or members that need to be treated and that are exposed in the occupied space, you can use a clear sealant so as to maintain the natural wood look, though the surfaces may become satin or glossy in finish.

To keep bats out of the cabin you'll want to find and screen off openings through which they have been entering. Look closely, as bats can enter a home or its attic through surprisingly small passages.

Bats are important to protect and preserve insofar as possible, though I agree we don't want them inside our homes. You might want to consult with local bat experts about installing one or a few bat houses or refuges in trees nearby.

Watch out: Histoplasmosis (from bat droppings) is an infection caused by inhalation of Histoplasma capsulatum. In people with compromised immune system this can be a particularly dangerous infection, potentially fatal if not treated. See also granuloma, iritis, lung nodules. More information is

Reader Question: can I use peppermint oil to repel squirrels or other animals?

I have heard that peppermint repels squirrels - is that true? - Anon 9/23/12


You might indeed want to try peppermint oil Anon, as a number of animal repellant products do indeed contain peppermint oil, such as some deer and cat repellants. There are mixtures for similar applications mix oils of peppermint, geranium, sage, lavender, eucalyptus, lemongrass etc.

But our research into common preparations whose effectiveness has been tested as a squirrel repellant shows some different suggestions. I've included details just below.

Watch out: some folks use mothballs as an animal repellent. Using mothballs for animal repellant is an illegal pesticide application and can cause other building odor or even health problems.

There are other specific animal repellent sprays and products sold at home and garden suppliers, often targeted to specific animals: coyote urine, for example. I've also tried pouring a bit of ammonia (or bleach but never BOTH at once) onto an area on a walkway or stair where a cat kept urinating.

List of Common & Effective Squirrel & Rodent Repellant or Rodent Aversive products

For rodents, which would include squirrels, some prepared products and specialty chemicals or preparations sold as repellents include:

  • Andrographolide
  • Aversives
  • Bitterants
  • Capsaicin oleoresin - found very effective even at low concentrations [9][10]
  • Colocynth
  • Denatonium Benzoate Bitterant (extremely bitter, used in a variety of products)
  • Denatonium saccharide
  • Natural and synthetic bitterants
  • Nonivamide
  • Trans-capsaicin
  • Castor oil, habanero pepper extract and white distilled vinegar have been used as a DIY spray and also are found in some patented squirrel repellant products

Return to Mold/IAQ Action Guide: What to do about mold, mildew, and other indoor allergens an environmental testing guidance website explaining what to do about mold, mildew, and other indoor allergens.


Continue reading at GOPHER HOLE DAMAGE or select a topic from the More Reading links shown below.


Or see BLACK STAINS from ANIMALS for a description of the cause and cure of various types of stains caused by pets or other animals in buildings.

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ANIMAL ENTRY POINTS in BUILDINGS at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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