If you can see daylight under the closed door, snow, water, and mice can get in too. Most gaps close with a new bottom seal. Some need a little more, like a floor threshold or new weatherstrip along the frame.
Quick answer: A gap under the door is usually a worn or torn bottom seal. If the seal is fine but the floor dips or slopes, a taller seal or a threshold on the floor closes the rest. Gaps at the sides and top mean the weatherstrip on the frame needs to be replaced.
Close the door on a bright day, turn off the garage lights, and look along the bottom and sides. Any line of daylight is a gap. Also look at the seal itself. If it is flat, cracked, stiff, or hanging out of its channel at one end, it is done.
On steel doors, the seal slides into an aluminum channel along the bottom edge. Salt and years of use bend and corrode that channel, and a new seal won't hold in a bad one, so we replace the channel when it needs it. On wood doors, we fasten a new seal to the bottom edge. Where the floor dips, we fit a taller bulb seal that fills the low spot. If water runs in or the gap is too big for any seal, we add a threshold to the floor under the door.
Then we set the opener's close limit so the door presses the seal down evenly, and we test the force so the door still reverses if it hits something. We also replace the weatherstrip on the sides and top of the frame if it has cracked or pulled loose. Our article on weatherstripping replacement in Wisconsin goes into the different types.
In Lake Country, the gap under a garage door does real damage. Wind drives snow under the door and it melts into a puddle on the floor. Salty water from the car sits against the bottom panel and rusts the bottom edge. If the garage is attached, the cold reaches the house through the door to the kitchen or mudroom. If you want to keep more heat in, see insulated vs non-insulated garage doors.
Send us a photo of the bottom corner of the door, taken from inside with the door closed. That shows the seal type and the size of the gap. We measure on site, and you get the price before any work starts. No charge to look at it.
Look at the bottom edge of the door. Steel doors usually have an aluminum channel with the seal slid into it, and the shape of that channel decides which seal fits. Wood doors usually have a seal nailed or screwed on. A clear photo of the end of the bottom panel is often enough for us to tell.
Sometimes. A threshold glued to the floor helps when the slab dips or water runs in. It does not help much if the seal on the door is cracked or torn. Many garages need both, and we will tell you which yours needs.
A thicker seal can make the door touch down sooner than the opener expects, so the opener reads it as hitting something and reverses. The fix is to adjust the opener’s close limit and test the force setting. We do that as part of every seal job.
It closes the biggest opening, which helps a lot. Mice also get in at the bottom corners where the seal meets the frame and through worn side weatherstrip. We check all of those, since a seal alone leaves the corners open.
Fall, before the first hard freeze. Cold seals are stiff and harder to fit.
