How to Protect Your Home from Rodents

A house mouse fits through a gap the width of a pencil. Rodent control in Colorado is a fall job: entry attempts climb through September and October, before the first hard freeze rather than after it. Sealing gaps larger than a quarter inch with steel wool, copper mesh, or hardware cloth stops most of them. Caulk and expanding foam alone do not; mice chew straight through both.

The National Pest Management Association estimates that rodents invade roughly 21 million American homes each winter. The timing matters as much as the number. Many homeowners start looking for help in December, when a mouse is already in the pantry. The households that avoid that point usually did their sealing in September.

Along the Front Range, the weeks between warm fall afternoons and the first hard freeze decide how the winter goes.

Rodent season starts earlier than most people expect, because rodents move toward shelter as nighttime temperatures drop, even while the days stay warm. Along the Front Range, that push begins in September, when afternoons are still pleasant. By the first hard freeze, most of the mice that were going to get in are already inside.

That is why late summer through early fall is the time to seal your house. Sealing in December is still worth doing, but by then you may be sealing some rodents in rather than out. The work is also harder in cold weather and frozen ground.

If you do only one rodent control job between August and October, walk the foundation and look for gaps where pipes and wires enter.

Mice almost never come in through the front door. They use openings most people never look at, and those openings cluster in six places.

• Gaps where pipes and wires enter. Where the gas line, water line, electrical conduit, or AC line-set passes through the foundation or siding. These are the single most common entry point and they are almost always unsealed or sealed with something a mouse can chew.
• Garage door corners. The bottom corners where the seal meets the track leave a triangular gap. Look at yours in daylight with the door closed; if you see light, a mouse sees a door.
• Dryer and bathroom vents. Damper flaps stick open or the exterior cover breaks. Both are open invitations.
• Gaps at the foundation and the beam above it. The joint where the foundation meets the framing, especially on older Littleton and Denver-area homes.
• Window wells and basement windows. Rotten frames, failed caulking, missing well covers.
• Roofline and soffit gaps. Rodents climb. A tree branch touching the roof is a bridge, and gaps where the soffit meets the fascia are the destination.

A house mouse can pass through an opening about a quarter inch across, roughly the width of a pencil. A rat needs about half an inch. If a pencil fits in a gap, so does a mouse.

When you seal out mice, the material matters more than the effort. Mice chew through expanding foam, silicone caulk, plastic, and wood without much trouble, which explains why so many carefully sealed houses still get mice.

What holds:

• Copper mesh or coarse stainless steel wool, packed tight into the gap. Rodents will not chew it. Copper is preferable to plain steel wool, which rusts and stains siding.
• Hardware cloth, quarter-inch galvanized mesh, cut and fastened over larger openings, vents, and window wells.
• Sheet metal or cement patching for foundation gaps and chewed corners.

The rodent control method that works is layered: pack the gap with copper mesh first, then seal over it with caulk or foam for weatherproofing and appearance. The mesh is the barrier. The caulk is the finish. Doing only the second half is the most common mistake homeowners make when sealing out rodents.

Yard changes help too, because they take away the places rodents gather before they move in. Keep shrubs and stored items about two feet from the outside walls. Trim tree branches back from the roof, and get firewood and lumber up off the ground and away from the house.

Because the two real costs are invisible until they are expensive. Rodents chew electrical wiring, and chewed wiring inside a wall is a fire risk that no homeowner sees coming. They also contaminate: mice and rats spread pathogens including Salmonella and hantavirus through droppings and urine, and they carry fleas, ticks, and lice indoors with them.

Then there is the compounding problem. A pair of mice is not a pair for long. Rodents reproduce quickly, and a problem that would have taken one visit in October takes much more in February. The cheapest rodent job is always the early one.

Insulation damage belongs on the list too. Rodents nest in attic insulation, and the combination of nesting, droppings, and urine can require removal and replacement of affected material rather than simple cleanup.

If you are hearing activity overhead and are not sure whether it is one mouse or a nest, call us at (303) 346-7087 before it becomes an insulation job.

You can do every step on this list yourself:

• Walk the full foundation line in daylight, looking for gaps where pipes and wires enter
• Close the garage door and look for light at the bottom corners
• Check that dryer and bathroom vent covers are intact and the flaps close
• Pack any gap larger than a quarter inch with copper mesh, then seal over it
• Fit or repair window well covers
• Pull shrubs, mulch, firewood, and stored items back from the walls
• Trim branches away from the roofline
• Store pet food, birdseed, and pantry staples in hard containers rather than bags

You have reached the limit when you hear activity in the walls or ceilings, or when you find droppings faster than you can clean them up. Finding a nest is another sign, and so are traps that keep catching mice instead of tapering off. The most important sign is this one: you have sealed every gap you can find, and the activity has not stopped.

If activity continues after a real attempt at sealing, the way in is probably somewhere you have not been able to see. Finding it is the skilled part of the job. Call Guardian Pest Management at (303) 346-7087, and we will inspect the house to track it down.

Guardian Pest Management is family owned. Sean and Michelle Meade have run it since 2000. We serve Highlands Ranch, Littleton, Castle Rock, Parker, Centennial, Lone Tree, Castle Pines, Greenwood Village, Roxborough, and Cherry Hills. Sean and Michelle personally bring more than 30 years of pest control industry experience, earned before Guardian was founded. That was earned before Guardian opened. We hold a 5.0-star Google rating in South Metro Denver.

A rodent call starts with an inspection. We identify the species and find the entry points and travel routes, along with hiding places and nesting areas, before any product goes down. After that, we explain what we found and what it will take to close those openings. Treatment and sealing follow from what the inspection turns up.

We tell you where the rodents are getting in before we treat, and bait is only one part of the plan. Home service never requires a long-term contract. If you have one entry point and one mouse, that is what we will tell you.

To have a rodent problem inspected before it compounds, call Guardian Pest Management at (303) 346-7087, or start at myguardianpest.com.

Related reading: Secondary poisoning, and what it means for pets and wildlife; Where DIY pest control goes wrong; Whether quarterly pest control is actually necessary; What to do about spiders in a Colorado home.