Inspecting for Animals: Tips for Home Inspectors

By Stephen Vantassel
Contributing Author, National Association of Certified Home Inspector
Project Coordinator, Internet Center for Wildlife Damage Management
Home Inspectors have the difficult job of trying to find out, “What is actually wrong with this building?”  Does the roof leak? Is the plumbing in good working order? Are the electrical outlets operational? But have you ever thought about the presence of wildlife?  You should. For not only shouldn’t a new homeowner not have to pay for a bat removal but learning how to inspect for wildlife will help make you a better inspector.  This brief article can only touch on a few issues involved in wildlife damage inspection. For a more detailed, but basic, introduction, visit our free online course at

1. Think like a mouse

Good wildlife damage inspectors view the world from a mouse’s perspective.  Mice are an important test species because if the house doesn’t have mouse problems, chances are it doesn’t have any other wildlife problems either. Like all animals, mice need food and shelter.  You should suspect that a structure has animal problems if the property had bird feeders, acorn trees or outdoor pets. Look around the property. Is it well kept? Are the wood and debris piles neat and frequently moved? If not, these areas provide spacious accommodations for rodents. Don’t be deceived into thinking the feeders and woodpiles are too far from the house for mice or other animals to reach. It just isn’t true. 

Black and brown speckles of bat droppings.
2. Look for small holes!!

Unlike bugs, mice need at least a ¼ inch opening (about the thickness of a standard pencil) to enter a structure. Please note that hole sizes only exclude possible suspects. Holes don’t conclusively identify which species is using the hole. For example, a mouse can use a squirrel hole but a raccoon can’t.  The following are some signs to look for when inspecting.
• Mice need ¼" size openings and leave rice seed type droppings scattered about. If you touch (gloved hands only) them they will be hard.
• Gray squirrels need a minimum of 1½" in diameter holes, but they’ll typically be about three inches. You may or may not find droppings.
• Bats need at least a 3/8" gap and their droppings will be concentrated below where they roost. Also the droppings will crumble like dust when disturbed.
• Birds need various size holes — one inch in diameter would be a minimum — but you’ll often see the tell-tale white droppings where they enter.
Holes are easier to locate if you start on the outside. Use a powerful flashlight (min. 500,000 candlelight) to illuminate dark areas. You have found a hole, if an area remains dark after illumination. The area remains dark because it lacks the surface required to reflect the light back to you.  Pay special attention to corners, gables, eaves and vents, and any place where two boards meet. Over the years, moisture and heat cause the boards to expand and contract until a gap forms. Animals will exploit these weak areas.
Raccoon den entrance

Get on a ladder and scan the gutter and roof area. (Follow all appropriate safety guidelines for working with ladders) Squirrels like to sit on the gutter and chew through the fascia board, which has been softened by water. Don’t be surprised to find gutters filled with leaves. Scan the roof for feces. Raccoons will often defecate on a roof before entering the attic or chimney.  Avoid disturbing the feces as they potentially carry a dangerous round worm called Baylisascaris procyonis. You can learn more about this worm at
3.  Check out the chimney

Two flues. One on right is uncapped. The left one looks capped but the screen is damaged offering an openning for animals to enter.
Chimneys are a special concern. Don’t take the clients’ word that the flues have been screened. Screening can rust through [see image above].  Homemade screening jobs are usually illegal, as they don’t allow enough clearance. Make sure your eyes do the job. A chimney can have more than one flue. Always inspect a chimney from the top first. Uncapped flues should be inspected for smudge marks and fur (which suggest raccoon presence) and spider webs (which suggest lack of activity). Be advised that even though raccoons rarely enter active furnace flues, it does happen. Although you won’t see or find any animals in most inspections, here are some rules of thumb regarding noises emanating from a chimney:
• Scratching, think squirrel
• Fluttering, think bird
• Chirping, think raccoon
• Grinding noise, think chimney swift (especially if the chimney is not lined with tile).
4. Inspect the foundation

Get on your knees and look for gaps around the foundation sill. Animals, like red squirrels, chipmunks and mice, can enter at ground/foundation level. Entrances will typically be around pipes, dryer vents, broken windows, rotted sills and cracked foundations.  Look carefully for wear or rubmarks around holes ¼" or larger. 

Inspect all the doors. Many times, hatchways and garage doors don’t close tightly. All of these gaps are potential entrances for a crafty creature.

Dirty smudge marks will often appear as the body oils of the creature rub off on the building. Investigate the corners of the house. Squirrels and raccoons climb gutters. Raccoon prints will look like brown smears and scratches will be deep and pronounced. Squirrels, on the other hand, will leave no prints and the scratches will be very fine. If tree branches hang over the roof, don’t be surprised if there are no signs of tracks. Consider all the ways and routes an animal might use to access a house.

5. Moving to the inside of the house

Inside wildlife damage inspections focus on the attic and crawl spaces. Be warned, however, crawling around attics, closets, and roofs is not only dirty, messy, uncomfortable;  it is also dangerous.

As you enter the attic, wear, at minimum, a HEPA filter mask. Attics, being confined spaces, can expose you to dust, insulation fibers and fecal matter that you don’t want in your lungs. Walk on the crossbeams.  If insulation obscures the beams,  use the trusses or move the insulation to help you find the beams.
Carefully inspect the vent screens. Sometimes they look intact from the outside, but an inside investigation can reveal they’ve been pulled away from the edge or chewed through. Turn your flashlight off and look for light entering the attic. If you see areas where the light is shining through, make sure it’s not due to a ridge vent or soffit vents. Modern houses have a lot more vents than older ones. Note all vents before you enter the attic. Mushroom vents are difficult to inspect because the mesh isn’t in plain view. Use your mirror to inspect the integrity of the mesh.
View looking down upon blown in attic insulation. Note the grooves and trails of mice.
Pay careful attention to the insulation. You would be surprised how much it can tell you. Dime to quarter-sized holes are often caused by mice or flying squirrels. Look for trails in the blown and loose fiberglass insulation. Mouse trails will look like someone lightly grooved the insulation by rolling a small rubber ball over the material [see image]. Obviously trails made by squirrels or raccoons will be very pronounced.  Fiberglass, removed from its paper backing, signifies the presence of squirrels. Always, keep an eye out for feces. While mouse feces are usually located under the insulation, there are exceptions.

Finally, if possible, stand up in the attic to follow the roofline down to the soffit area. It’s in these soffit areas that squirrels in my area like to live. Standing is usually the only way to see the soffit area because it lies below the level of the attic floor. If it’s too dangerous to crawl around the attic, try to get a good look at it while standing in a safe place. 
6. Look for signs of past problems

Just as a new paint job on an older car should send up a red flag, so too should the house that has all the preventative steps taken for wildlife. For example, if the house has hardware cloth installed over the attic vents (from the outside), consider that it might have had problems with squirrels or raccoons. In my experience, homeowners rarely take preventative measures. They usually only install what is needed to prevent future problems only after having the problem. Preventative measures that should raise your suspicion include:
• Finding mouse poison (or empty toxicant boxes)
• Vents screened with hardware cloth
• Dryer vents and other exhaust vents screened
• Aluminum flashing (painted or otherwise) installed at the eave level. Usually a squirrel hole was repaired here
• Stainless steel chimney caps
• Wire screening around porches and decks to prevent skunk and woodchuck habitation.
Don’t get overwhelmed with the information presented here. As inspectors, you already have a number of things to consider when inspecting a house. However, if you can incorporate some of these investigative techniques with regard to animals, you’ll have added that much more professionalism to your work and value for your client.

©Stephen Vantassel 2005

About Stephen Vantassel: Stephen Vantassel is the webmaster for the Internet Center for Wildlife Damage Management.  ICWDM provides free, research based information on how to mitigate damage caused by wildlife.  He has published two books, The Wildlife Removal Handbook, rev. ed. and the Wildlife Damage Inspection Handbook rev ed., as well as numerous articles.  Stephen is a regular contributor to InterNACHI and is also available for conferences and workshops. You can contact Stephen Vantassel at .
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