How to Keep Mice Out of Your House or Camper
The view from our back porch is into lovely woods. We love sitting out there, listening to the birds, watching turkeys strut out of the brush, and just enjoying nature.
The squirrels, the turkeys, the songbirds, and the hummingbirds have a nice view of our home too, but don't have any interest in coming in to join us. The mice, however, that live near the tree line see our home as a convenient source of warmth and food, and would love to live inside with us, especially in cold weather.
We would prefer that the mice stayed in the woods.
We realize that they were here before we were. Their families may have been right here for hundreds of years, maybe thousands, maybe even millions. In a species-neutral court, I'm sure they could argue that they have more right to live here than we do, so their transgressions into our space are perhaps justified.
Or so they would argue if they could.
Not Welcome Here, Sorry
In spite of the obvious injustice, we intend to keep mice out of our home. They get plenty of spilled bird feed as reward for giving up their land, and that's all the consideration they will get from us. Well, that and we do toss out some stale bread now and then. If they can get to that before the birds do, they are welcome to it.
Poison Is an Option
We have a contract with a pest control company. We pay them $300 a year and they come around regularly to take care of wasp nests, ants, and anything else that is encroaching on us. I don't like doing that, but I don't want my house overrun with insects either, so I grudgingly accept that.
And I really do not like the idea of poisoning mice; but yes, I let the pest control people put down the poison bait. It's the kind that makes mice thirsty and hopefully drives them out of the house to find water and die.
What can you do? Mice are filthy, they carry disease, and they will literally chew the house apart. They leave their droppings everywhere, it's disgusting and we cannot put up with it.
Ultrasonic Pest Control Devices?
You've seen them. We tried them at our old home; they did nothing.
Just Stay Out
I'd prefer that mice just wouldn't get in the house to start with. If they don't come in, I don't have to find their droppings or throw out cereal boxes they have chewed into. If they don't come in, they don't have to eat the poison that sends them to an unpleasant death. So let's just keep them out to start with.
They say that a mouse can squeeze through a hole small enough to push a pencil through. If they can get their head through, they can wriggle the rest in. In a typical house, there are holes far larger than a mouse's head. These are big open doors for mice to walk right through.
Lazy Contractors Create Holes
A lot of these holes are created by lazy contractors. When they install pipes or wires that enter your house, they usually drill a hole far larger than they need, and few will even make a token effort at closing it up. Those holes leak heat, which is bad enough from a cost point of view, but consider what that outflow of warm air means to a mouse scuttling by on a frosty fall morning.
Warm air? Wow, that's better than being out here! And look, a big hole I can go through. Let's see what is in here ... is that food I smell?
Look for holes. I plug them up with a mixture of caulk and copper wool—it's like steel wool, but made from copper. I use that because it doesn't rust away like steel wool. I have used Brillo pads at times; I figure the combination of soap and steel wool can't be fun to chew through.
With any of that, you have to check it regularly. The caulk dries up and will fall out.
If your siding is loose, mice might be able to climb up underneath. That's not usually easy, but it's worth checking. I found one side of my house was loose enough to get my fingers under it easily - I stuffed some copper wool up there just in case.
Holes Around Pipes
Having mice in the walls and ceilings is bad enough, but they are going to try to find a way into your living space too. One of the more common entry points is the pipes to your sinks and other appliances.
In my home, the hot and cold water come up through a two-inch hole in the floor and then split off to go up to the vanity. A mouse that got into the space under the floor could easily climb up those plastic pipes and now be under the vanity. From there, they might find their way out, or just set up shop there, very warm and cozy.
"Great Stuff" Expanding Foam
I use "Great Stuff" expanding foam to fill in spaces like that. I can just lift up one the caps in the vanity, stick in the nozzle, and fill it up. Yes, the mice can chew through it, but it isn't an open invitation any more.
Electricians Leave Holes
We had an electrician run a new plug in our garage and he made big holes in the sill of the house to bring the wiring in. Shortly after that, we had ants. I was sure that was from the work he did; it was too coincidental. Of course we called the pest control people, but I wanted to fix the electrician's sloppiness too because the holes were easily big enough for mice.
He did his work from underneath, where it is difficult to get at, so I drilled holes in the garage wall above where he worked and filled it all up with foam. Eventually I will get someone to go into the crawl space and seal it up from that side too, but this will help.
There is no point in inviting critters in!
Basement Windows and Crawl Space
I was surprised to find that my crawl space windows were just such an invitation. The problem is that the bottom of the window isn't flush with the sides: it's at a slight angle. The screen that covers the window has a large gap, which would again leak warmer air to the outside even when covered by the glass windows we put on in cold weather. As you can see in the pictures, the gap is more than large enough for a mouse.
I used self-stick insulating foam tape to make a better seal. That's not ideal, because mice can still chew through it. I may have to dig out the earth and straighten these out, but I need to figure out some way to keep them straight. At least the foam keeps warm air from flowing out and attractiing mice, and if they do chew through, I will be able to see that when I pull the windows to inspect the crawl space.
Lazy contractors again. If you pull off your cabinets, you'll probably find holes in the walls behind them. If mice manage to get in from outside, these holes can let them in behind your cabinets.
Our cabinets are closed up, but there is space underneath, and that's where lazy contractors left a big exit to the kitchen. You can see where I used duct tape with steel wool behind it to plug these up. You can't see the fix unless you lay on your stomach on the floor, so I wasn't concerned with being neat.
Of course, the main thing is to keep mice out of the walls by closing off the outside entrances, but if they do manage to get in, it's better to hear them in the walls than have them get out into your living space!
Leaky Cabinet Work
I found this recently: I've stuffed it with a paper towel so you can get an idea of the size; it is plenty big enough for a mouse to crawl out of.
Could mice get to this place? I don't know, but when I put my finger near it, I could feel cold air, so it is a heat leak at the least.
I'd love to tear out these and the kitchen cabinets and really seal everything up, but I'll have to settle for expanding foam. The paper is just temporary until I can get to the foam, but if I find it pushed out in the meantime, I will know for sure that mice can get to there. I wouldn't be surprised, because I'm sure there are big, sloppy holes for the pipes and drains. I'm going to drill some holes in the cabinet floors near those drains and try foaming those up. That's blind work, of course, but better than doing nothing.
Speaking of that, these homes have a plastic covering underneath that is supposed to keep critters out. "Park Model" camper-trailers may have something similar. We have that covering inspected and patched yearly, but the inspectors might not notice small holes and tears; it's not fun sliding around under there, and they tend not to spend a lot of time. I'm thinking of building a little robot camera I can send under there to look for problems, and inspect repair work people supposedly did and find sneeded repairs they didn't notice in their haste.
The screening is thin stuff, and the pest people told me they have seen mice chew through it. They advised getting some heavier stuff to install behind it. I want to do that, but we don't want it to look ugly; these windows are mostly hidden by bushes, but not completely. I have to think about how best to do that.
What You Can Do Outside
Keeping brush and wood away from your home keeps mice from living near you. The nearer they live, the more likely it is that they will spot an invitation.
Do It Yourself?
I said above that we pay a pest control company. Some of my neighbors buy the poisons themselves.
I'd rather leave it to the pros. But if you want to do that part yourself, or aren't sure, you might start with Habee's article Mice and Rats: Exterminators or Do It Yourself? It's certainly cheaper, although $300 a year with unlimited service calls isn't much.