Home & Garden Columns

About the House: Little Visitors in the House

By Matt Cantor
Friday January 25, 2008

When you crawl around under houses every day, you see some odd things. It’s part archaeology, a little zoology and, of course, all that construction stuff. It doesn’t take too long doing this to realize that you’re not always alone down under the house (or up in the attic). There are little neighbors that like to share the space. They’re not trying to get inside your house, per se. It’s just that they want a safe warm space and you happen to be right there. Termites use the same logic. They don’t know that they’re eating a house. What’s a house to a termite. They’re just eating some fallen trees that happen be in their path.  

One of my favorite critter sightings, and I’ve seen this a number of times, is seen in a crawlspace. It’s a pile of empty snail shells mounded up like a stack of beer cans on a bachelors beaten-up coffee table. It took me a while to figure it out but apparently, raccoons like snails and will collect a bunch of them, kick back under the house and snack away. Are raccoons French? 

A range of animals also live out their lives, fight, give birth and die under and inside houses. At least one or twice a year, I’ll get a call that has to do with animal sounds in a wall, attic or below the floor. If they can get in, all the things that would be happening in the woodland will occur in your house at 3 a.m.; and you get to listen. (That seems to be a favored time for figuring or amour d’bete). 

Some odd few may enjoy these interlopements but most people prefer to keep the wilds outside. If you are among the latter, you may wish to avail yourself of some of the following strategies and data. 

First, mice and rats get inside of almost everyone’s house. If you see evidence (scatological or otherwise) don’t be surprised. Rodents come into houses for warmth, food (when they can get it) and to escape predators, which is why they like the tiny entryways that bar the cat but allow the mouse. 

Mice are very small, smaller than they look. Their skulls are somewhat flexible and they are more fur than flesh. Field mice can enter through openings smaller than one half inch in diameter. Rats vary in size but can also squeeze through three quarter inch openings below doors or around pipes. To prevent these from entering, you will need to begin by identifying every tiny opening in the side of your building. Louvered metal or wooden vents often allow for rodent entry. Replace louvered (with stamped out slits that you can fit your fingers through) metal vents with ones made of quarter inch galvanized steel mesh. Caulk the back rim and screw them in place. 

If you have an old house with wooden foundation vents, you can install the same quarter-inch steel mesh on the inside of these without ruining their marvelous grandmotherly appeal. Take a roll of mesh and a pair of tin snips and cut a rectangle two to four inches larger in each direction than the vent space. Cut away the corners so that you have four tabs that you can bend onto the adjacent jambs or framing or simply snip into the corners diagonally and fold then over each other. Affix these firmly in place using a staple gun and half inch long staples. 

You can do the same thing behind half inch steel mesh vents or any grate that has a larger than one centimeter opening. 

Look carefully around the doors to your electrical or gas compartments. Many do not fit tightly and are virtual rat freeways into your house. Some doors fit so badly that the only real answer is to replace them and make the replacement a nice snug fit. Some doors can be altered with a piece of trim. Remember that a small opening for you may be huge to an animal. 

By the way, once their under the house, there are loads of vessels, chaseways and separations between the crawlspace and the inner walls for critters to traverse so keeping them out at the perimeter is the easiest way. 

Gaps around plumbing, especially large waste lines, are very common. Gaps can be caulked using a good quality caulk. I like polyurethane caulks for their ability to grasp porous materials such as wood. Sikaflex is one good brand. For larger openings you can decide if wood and nails are the answer or something like expanding foam. Keep in mind that rats can eat through foam. If you do use foam, it should be covered over with wood, paint or anything that can minimize exposure.  

For larger openings, mesh can be secured in place thus preserving more ventilation. 

Large mesh areas can be torn out by raccoons and it may be wise to double the mesh. I like a combination of quarter inch mesh and chicken wire. Very large openings can be a combination of quarter inch mesh and welded wire (which comes in a range of mesh sizes and is very heavy duty). 

While you’re at it, it pays to check your attic vents. Many have very large openings and I’ve seen more than a few full sized bird’s nests as evidence. Since bird feces can be virally rich, birds nesting should be considered a real health hazard. 

While it’s nice to make sure the doors to your house fit well for energy conservation reasons, a large bottom gap is also how mice can get inside. This too, is worth looking at. The last one I’ll mention is perhaps the least likely but I have seen evidence of animal entering through roof vents these, too, can be screened except in the case of gas appliances and dryer vents (which shouldn’t go through your roof anyway but, hey, there they are). 

If you’ve really worked your way through all of this, you are in much better shape and likely to have fewer all night parties raging in the wall. A determined animal may still enter by burrowing or may gnaw through a wooden barrier but this isn’t worth worrying about. Deal with that when you have the evidence. 

Ants can’t be stopped by any of these methods so don’t try. Keep the kitchen floor clean and take out the garbage regularly. If that doesn’t do it, you may need to use one of the nasty agents that we all prefer to avoid. Grant’s Ant Stakes work pretty well but be sure to follow the instructions. 

Many a night as I drive home, my headlights catch the eyes of a deer on my curvy little Berkeley street. How lucky we are, I think, to live in a time and place where life flourishes and lives safely among us. While I may not want to hear raccoons fighting over dinner late at night, their presence in my neighborhood is a blessing. I don’t want to live in a city devoid of animal life and if I have to work a bit to corral them, oh well, it’s a small price. 



Photograph by Matt Cantor. 

This wooden ventilation screen, seen from the inside, lets in six rats at a time.