The Garage-Door Threshold: the Easiest Fix You're Not Making.

Stand inside your garage in the daytime with the door closed and the lights off, and look at the bottom corners of the door. On most Oregon homes you will see two small triangles of daylight, one at each end, where the curve of the door meets the slab. Those two triangles are, quite often, the single largest unguarded opening into the entire house — and the garage is rarely just a garage. It connects to the kitchen, shares a wall with the living space, and stores exactly the things rodents want: pet food, birdseed, garbage, garden seed, and cardboard to nest in.

Two triangles of daylight at the bottom corners of the door. That is the gap, and it is the easiest one in the house to close.

Why the corners always leak

A garage door is a stiff panel running in vertical tracks, and the rubber astragal along its bottom edge is designed to seal against a flat, level slab. Two things defeat it. First, almost no garage slab is perfectly flat — it was floated by hand, it has settled, and it slopes slightly for drainage — so the straight rubber seal bridges the low spots and leaves voids. Second, the door's bottom corners are where the seal curves up into the track, and that radius leaves a triangular gap that the astragal was never shaped to fill. The result is two persistent openings at precisely the ground-level height a rat or mouse travels, often large enough to put a thumb through.

A house mouse needs only about a quarter inch. A Norway rat will work a half-inch gap, and a rat that finds a smaller one will gnaw the rubber and the wood trim to enlarge it — garage-door corners are a classic spot to find fresh gnaw damage. Because the garage is dark, sheltered, and full of stored food, an animal that gets through the corner often does not need to go any further to be comfortable.

The fixes, cheapest first

1. Corner seals

The most targeted fix is a pair of garage-door corner seals — molded rubber or plastic pieces that mount at the bottom corners and fill the triangular gap the main astragal leaves. They are inexpensive, install with a few screws or adhesive, and address the exact spot that fails. For many homes this alone closes the opening.

2. A fresh bottom astragal

If the rubber along the bottom of the door is cracked, hardened, or chewed, replace the whole astragal. A new, supple seal conforms far better to the slab, and on doors with a T-style or bead retainer the swap is a straightforward afternoon job.

3. A threshold seal on the slab

For a slab that is visibly uneven or sloped, a garage-door threshold seal — a raised rubber strip glued to the floor that the door closes against — bridges the irregularity from below. It pairs well with corner seals and is the better choice where the floor, not the door, is the problem. (One caveat for the wet side of the state: a floor threshold can pond water against the door in heavy rain, so weigh drainage before choosing it.)

4. Seal the perimeter and the service door

While you are there, finish the job. Check the weatherstripping along the sides and top of the door, the gap under the walk-in service door (it needs its own sweep and threshold), and any gaps where the framing meets the slab. The garage is also where the rim joist, utility penetrations, and the door to the house all converge, so it rewards a few extra minutes.

The part everyone forgets: the connecting door

Closing the garage door corners keeps rodents out of the garage. But the door between the garage and the house is the one that protects your living space, and it is frequently the leakiest interior door you own — a big gap under the slab, no sweep, and an unsealed threshold. A mouse in the garage is an annoyance; a mouse that walks under the kitchen door is in the house. Add a door sweep and seal that threshold, and you have built a second line of defense behind the first.

Why this is the best hour you can spend

Exclusion work is usually a question of effort versus payoff, and the garage threshold sits at the top of that ranking. The materials cost a fraction of a single service visit, the tools are a screwdriver and a caulk gun, and the gap you are closing is both large and high-traffic. We routinely find that a home with a recurring "mice in the kitchen" problem is really a home with two open garage corners and an ungasketed connecting door — and that fixing those two things does more than any amount of trapping. Walk out to the garage, close the door, and look at the corners. If you can see daylight, you have found an afternoon that will pay for itself.