How to Keep Pests Out of Your House

Shore up your lines of defense against unwanted guests.

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Step 1: Find the passages that let pests in

Pests becoming a problem in your house? With a few hours work you can block most of their entry points. Here are the key areas to inspect:

Wall penetrations:
Search for gaps around anything that passes through your walls such as gas, plumbing and AC lines, phone and TV cables and exhaust vents. Siding: Gaps and holes in siding and around trim are usually obvious. But also look under the siding where it meets the foundation. Rot, foundation shifting and sloppy building practices can leave openings there.

Doors and windows:
Look for torn screens and worn-out weatherstripping that might provide an entryway for bugs. If mice are a problem, make sure the rubber gasket under your garage door seals tightly to the floor (replace the gasket if it doesn't seal).

Look for foundation settling cracks in masonry and make sure basement windows close and seal tightly. If there's a crawlspace under your house, all the floors above the space are potential entry zones. If the crawlspace is accessible, put on safety glasses, crawl inside and inspect it with a flashlight.

Sometimes you can locate passageways from indoors. On a sunny day, light peeking into a dark basement, garage or attic reveals gaps and cracks. A heavy concentration of cobwebs indoors can also indicate an entry point.

Foliage or wood piles:
Anything touching your house can provide a freeway for bugs. Tree branches, for example, can spell trouble even high above ground level. Ants that feed on aphids in trees use branches as a bridge to your house. The solution is to trim back branches.

Dryer vents and exhaust fans:
Be sure that dampers open and close freely. Trouble starts when a sticking damper stays open and leaves a welcoming entrance for all sorts of critters, including birds and squirrels.

Soffits and roof:
Look for holes and gaps in soffits and fascia, especially where they run into adjoining rooflines (these are favorite entries for squirrels, bats and wasps).

Roof vents:
A missing or chewed-through screen on roof vents lets squirrels or bats into your attic.

Chimney caps:
Add chimney caps if you don't already have them. They prevent birds and rodents from making the firebox of your fireplace their summer home.

Debris-filled gutters are a favorite nesting spot for corn ants.

Figure A: How Common Household Pests Get In

Your home is an inviting place for many types of pests. But with a little maintenance savvy, you can keep them out.

Common pest entries

Step 2: Eliminate pest entrances

Chances are you'll find several entry points in your walls, foundation or soffits. Fortunately, these gaps and cracks are easy to seal. For those smaller than 1/4 in. wide, acrylic latex caulk is a good filler because it's inexpensive, paintable and easy to apply. But acrylic caulk won't last long in wider gaps. For gaps and cracks 1/4 in. up to 1/2 in. wide, use polyurethane caulk. Polyurethane is gooey and more difficult to use than acrylic caulk, but you can smooth and paint it for a neat-looking job. Keep a rag and mineral spirits handy to clean up accidents.

Expanding foam is a fast, convenient filler for anything wider or for areas where appearance doesn't matter. It can fill gaps of any size but doesn't leave a smooth, neat-looking patch. And rodents can gnaw right through foam, so it's smart to stuff gaps with copper mesh before you add the foam. Conventional steel wool can eventually rust away. If you only have a few gaps to fill, buy a box of copper scrubbing pads from a hardware store or online. If you have holes galore, it may be cheaper to purchase a professional copper mesh product like CopperBlocker, which is available online. For most cracks, “minimal expanding” foam is the easiest to use (standard foam expands too much, flows out of the crack and makes a mess). A little overflow is no problem, since you can slice off the excess. For large or hollow cavities, standard full-expansion foam is the best.

Step 3: Deprive bugs of moisture

Insects and other small pests need to draw life-sustaining moisture from their surroundings, so they avoid dry places and are attracted to moist ones. If the soil around your house, the foundation and the walls is dry, it'll be less attractive to insects, spiders and centipedes.

There's no way to keep everything perfectly dry, of course, but you can reduce moisture. Here are common moisture sources and ways to reduce them:

Downspouts and gutters:
Check that the downspouts are turned away from the house, and invest in a splash block or downspout extensions to disperse rainwater. Also watch for major leaks in your gutter system that may be pouring water onto or near your foundation.

Standing water:
If water is not absorbing into your lawn, your grass may have a buildup of thatch. The solution is to aerate your lawn to open up dense patches and admit water better.

Poor drainage:
Make sure that the soil is sloped away from the house at least 6 in. over 10 ft. This will reduce soil dampness near your foundation and keep your basement drier.

Mounded mulch:
Mulch and soil trap moisture and should be raked away from your windowsills and any other wood (Photo 1).

Heavy vegetation:
Plants growing against the house will keep siding damp. Trim back bushes and trees.

Plumbing leaks:
Fix leaks such as a dripping hose bib. If your home is above a crawlspace, look for leaks from any exposed plumbing under the house.

Moisture problems can come from inside the home too. A leaky sink trap, for example, can create a moist bug oasis under your kitchen cabinets. A poor seal around a bathtub can allow water into the surrounding floor and walls. Damp basements are a favorite home for spiders, centipedes, millipedes, silverfish and sowbugs.

Step 4: Eliminate clutter

If pests are the enemy, then clutter is the battlefield. Any pests you can name love our untidiness for a couple of reasons: to hide their initial infestation and provide privacy and shelter for reproduction. The best way to eliminate pest homes is to store items properly. Garages often harbor many clutter zones and are easily accessible to critters. Add to that the seductive smells of pet chow and your garage will look pretty darn cozy to pests looking for an upscale home. Birdseed and pet food need to be stored in containers that mice and other rodents can't get into. Avoid keeping old cardboard boxes in your garage, but if you must, make sure they are broken down neatly, stored off the floor and inspected regularly.

Neatness deters pests indoors, too. Keep cardboard boxes and even plastic bins off the floor and on a wire rack or shelf. Be especially rigorous on concrete floors. Moisture forms between the concrete floor and the box bottom (silverfish especially love damp spaces under boxes). Another reason to use storage racks is for easier pest inspections. With boxes off the floor, you can quickly spot mouse droppings and other evidence of unwanted critters (Photo 1).

The cabinet under the kitchen sink is a potential pest nirvana with trash, moisture, clutter and dark hiding places. Infestations can be hard to spot under all the sponges, rubber gloves and paper bags. To get on track, take everything out of the cabinet and stick self-adhesive vinyl tile squares to the cabinet floor. These tiles are cheap (at home centers) and easy to wipe clean. Next put all your cleaning supplies in a tote so you can easily remove them to inspect and clean (Photo 2). While you're under there, be sure to check for plumbing leaks.