There was a time when I lived in the houses I was restoring. The oldest of these was a 1787 center-chimney Cape. I was sitting in our temporary kitchen/living room, reading a book and having a cup of tea when a rat the size of a brown bear strolled into the room. Two throwable items were close to hand. A grapefruit and Amelia, our cat. I woke Amelia. She wearily opened one eye, took a casual look, and went back to sleep. I threw the grapefruit and the rat sauntered off. Amelia was a scrap of a cat but tough as can be. She finished off the rat the following day. Not every cat is a great mouser, or ratter, like Amelia, but most houses are an appealing residence for mice. Mice, on the other hand, are fairly inconsiderate houseguests. Keeping them out can be challenging.

My current project is a large old house in need of complete restoration. As I move forward with repairs, I do so with the goal of making the house rodent-proof. Mice are looking for one of two things: food, or shelter. If you don’t want mice, you need to not allow access to food, and you need to block their access to the interior. An adult mouse can fit through a hole the size of a dime. A rat can gnaw in through a 1⁄2" gap. Mice and rats have very flexible rib cages. If they can get their heads through a hole they can flatten their bodies to get by. It’s quite amazing.

Let’s use what we know of their behavior to help keep them out. Rodents are impressive gnawers. Their teeth work very well on wood and other organic matter. Metal in many forms will create an effective barrier. Any entry points of over 1⁄4" can be stuffed with steel wool, then caulked over to hold it in place. Holes drilled for plumbing and electric lines are good candidates for treating this way. Larger holes can be backed, prior to patching, with 1/4" hardware cloth.

Squirrels are responsible for the larger exterior holes on my project. Today I was faced with repairing holes about 4" x 6" on a section of soffit and fascia. The boards were fairly easy to get to and in poor shape beyond the gnawed bits, so replacing them made sense. Last week I was dealing with 3" round holes chewed through exterior moulding. The moulding profile is no longer available so repairing it was the way to go. First, slide a scrap of backing wood in through the hole and attach it to the moulding. Next, partially fill the hole with expanding foam. While the foam is wet, pack in steel wool. Once the foam has cured I like to complete the patch with Durham’s water putty. If you prefer, Bondo or epoxy can be used.