Sealing a 1920s Detroit Bungalow Basement Against Mice and Rats

Why are older Detroit bungalow basements so open to mice and rats?

Older homes carry many small openings from decades of settling, repairs and added utilities. A full basement with a masonry or block foundation, an old coal chute and a wood sill plate gives rodents several low routes in. The age of the house does not cause the problem; the gaps do.

Detroit has a large stock of bungalows and two-family flats from the 1910s to the 1930s, many with full basements. That is a general description, not a promise about your house, but it points to a pattern worth checking. Foundations built from block or rubble can crack along mortar joints. Wood sill plates settle and shrink. Coal chutes, once used for deliveries, were often left behind when homes switched to gas or oil. Every utility added in later decades, such as cable, gas, a dryer vent or a new water line, meant another hole in the wall.

Seen from a mouse's side, a basement is the warmest and the quietest part of a house in November. From a rat's side, a foundation crack or a gap near an old sewer connection can be an entrance. The house does not need to be dirty for animals to find it. It only needs a route.

That is the idea behind rodent exclusion: remove the routes, not only the animals. It is the same reasoning in our page on rodent exclusion for basements and coal chutes, and it ties in with when mice come in, because timing matters as much as technique.

Which gaps should you check, and what seals them?

Check the coal chute, utility penetrations, sill plate, foundation cracks, vents, doors, windows and floor drains. Seal them with materials rodents cannot gnaw: metal mesh packed into small gaps, hardware cloth over larger ones, masonry patch for block and concrete, and a durable sealant over the top.

The table below walks through the usual entry points of an older full-basement home, why each is vulnerable, and what is typically used to close it. It is a guide for what a technician looks at, not a script for every house; each building has its own pattern.

Work slowly, and with a flashlight. Look for dark smears on edges, where an animal's oily fur has rubbed along a gap, and for fresh dust or droppings near an opening.

What about the coal chute?

A coal chute is a direct opening from outside into the basement, built to move fuel. If the chute door is damaged or missing, or the cover is loose, it is a ready entrance. Close it permanently from the inside with masonry, or seal a metal plate tightly into the frame, and check the surrounding mortar.

Many older Detroit homes kept their chutes after the coal furnace was removed. On the outside, the door is often a small iron or wooden panel at the base of the wall, sometimes hidden by shrubs or a porch. On the inside, there may be a bin or a framed opening. If your basement has a bricked-in corner or a metal panel low on the wall, it may be a chute.

Check the door for rust and gaps at the hinges and edges. Look at the mortar around the frame for cracks. A chute that cannot be opened from the inside is a good candidate to close with masonry. Never remove a chute opening without thinking about the load above it; if the chute sits under a porch or a heavy wall, ask a mason or contractor.

If you are unsure what you are looking at, a technician will identify the opening and recommend a repair. The aim is a patch that is as strong as the wall around it, since rodents work at the weakest point.

What materials work, and what fails?

Metal and masonry work: coarse steel or copper mesh, hardware cloth, cement or masonry patch, and metal flashing. Expanding foam, plain caulk, rags, wood and plastic mesh fail because rodents chew through them. Foam can still be used as a backing if a metal or masonry layer sits over it.

A rodent's front teeth keep growing, so gnawing is a habit, not a choice. Soft materials are an invitation. A bead of caulk across a half-inch gap may be gone in a week. Foam is easy to apply and easy to chew. If it is the only barrier, expect to see it with a hole.

Use a layered approach. Pack the gap tightly with coarse metal mesh, which rodents dislike chewing, and then finish with a sealant or masonry patch to hold it in place and keep out drafts. For larger openings, such as a vent or a missing section of foundation, cut hardware cloth to size and fasten it on all sides with screws and washers.

Rats are stronger and larger than mice, so the materials need to be sturdier and the patches need to be firmer. A mouse-sized fix may fail against a rat. If you have seen large droppings, gnawed wood or a burrow along the foundation, see Norway rat control for how that work differs.

• Works: coarse steel or copper mesh packed into the gap
• Works: hardware cloth screwed down over vents and larger openings
• Works: masonry patch or cement for block and concrete cracks
• Works: metal flashing and fitted metal plates
• Fails alone: expanding foam, plain caulk, rags and paper
• Fails alone: wood, plastic mesh and soft rubber

In what order should you do the job?

Inspect first, trap or remove any animals already inside, then seal, then monitor. Start outside and low, then work upward. Doing it in this order avoids sealing animals in, and lets you test whether the seals hold. Aim to finish by the time the first frosts arrive.

Walk the outside of the house first, with a flashlight even in daylight, and mark every gap with chalk or tape. Then do the same in the basement. A gap that appears on both sides is a confirmed route. Photograph what you find; it will help if you call a technician.

Before sealing, make sure the basement is clear of animals. Set traps near droppings and along walls for several nights and see if anything is caught. A technician will typically handle this, and will advise on safe traps and on what to do about animals that may be in the walls above. Closing a hole with a mouse behind it can send it deeper into the house.

Then seal, starting with the largest and lowest openings. After that, check for new droppings, fresh gnawing or noise for a week or two. If the signs continue, there is still an entry or an animal. Keep storage off the floor and away from the walls, which makes later inspections easier.

If the job is large, or if you are in a two-family flat and the shared walls are a worry, it can be worth asking for help. The cost guide, How much does pest control cost in Detroit?, explains how basement access and the number of entry points change the work.

What about rats, sewers and the buildings next door?

Rats add three questions: whether a sewer connection or drain is open, whether the foundation has burrows along it, and whether nearby buildings are empty or being demolished. Residents report that rats move into neighboring homes when buildings come down, and the city handles rat harborage on neighboring properties.

Orkin ranked Detroit seventh in its 2025 list of the cities with the most residential rat calls, up from eighth the year before, and the ranking reflects only that company's calls. One local pest firm has also reported an increase in rat calls across the metro area. Suggested reasons include empty buildings, demolition and wetter summers, though the cause is not clear.

For a homeowner the practical meaning is simple. Seal what you can on your own property. If you suspect an old sewer connection or a cracked drain, a plumber can check the line, since a technician cannot fix pipes. If rats seem to come from a neighboring vacant house or lot, Detroit's Buildings, Safety Engineering and Environmental Department handles rat harborage under the city's property-maintenance and solid-waste codes, and residents can report it through the Improve Detroit app.

None of that is a judgment about any neighborhood. Vacant property is part of the landscape in parts of the city, and pest work simply has to account for it. For the deeper picture, see our guide on rats near vacant lots.