A homeowner notices a draft creeping across the garage floor all winter
It started as a cold ribbon of air along the baseboard of the attached garage, the kind you feel on your ankles when you step out to grab something from a shelf. The homeowner blamed the furnace at first, then the old window at the back. Only after a January cold snap did they crouch down by the garage door and see daylight running the full width of the threshold. Air was pouring in under a door that looked, from a standing height, perfectly closed.
That thin line of light is the most common failure in the whole system, and it rarely fixes itself. It usually means the seal that once pressed against the floor has given up. Understanding why it fails, and what fails alongside it, tells you whether you’re facing a ten-minute fix or something larger.
The bottom seal that flattens, cracks, and stops doing its job
The strip of rubber or vinyl along the bottom edge of the door does the hardest work of any seal on the assembly. Every time the door lowers, that strip compresses against the concrete to close the gap. Over years of cycles it loses its memory. The rubber flattens, splits at the ends, and hardens in cold weather until it can no longer conform to the floor.
Across the upper Midwest, freeze-and-thaw cycles accelerate the damage. Rubber that goes brittle at fifteen degrees cracks where a warmer climate might leave it pliable. When the bottom seal fails, replacing it is straightforward on most doors: the old astragal slides out of a retainer track along the door’s edge, and a new one slides in. The trouble is that a fresh seal only works if the floor beneath it is even and the door still sits square.
Gaps along the sides where the jamb weatherstripping has pulled away
Run your hand along the vertical edges where the door meets the frame and you’ll often find the second leak. The weatherstripping nailed to the wood jamb is meant to hug the door panel, but nails work loose, the vinyl flap curls back, and sun-facing sides dry out faster than the shaded ones. Once that strip separates from the door by even a quarter inch, wind finds the opening.
This stop molding is inexpensive and sold in pre-cut lengths, but it has to be positioned with the door closed so the flexible lip just touches the panel. Nail it too tight and the door binds; too loose and you’ve fixed nothing.
Why the top of the door lets in more than you’d think
The top edge gets ignored because you can’t see the gap without looking up, but it can leak as badly as the bottom. A header seal mounted along the top jamb closes the space between the top panel and the frame. When it’s missing entirely, which is common on older installations, warm air escapes and cold air draws in along that whole upper line. It’s a small strip that makes a surprising difference on a heated garage.
How an uneven slab and a warped panel widen the gaps over time
Seals don’t fail in isolation. A concrete slab that has settled unevenly leaves the door meeting a floor that dips on one side, so no straight seal can close it. A bottom panel that has warped or bowed from moisture pulls its edge away from the frame. Rollers that drift out of alignment let the whole door hang crooked in its opening. In each case the visible symptom is a draft, but the cause is structural, and swapping the rubber only buys a season before the gap returns.
The pests and water that follow a failed seal indoors
A gap that admits cold air admits everything else too. Mice need less than a half inch to get in, and a lifted corner seal is an open invitation. Meltwater and driving rain run under the threshold and pool on the garage floor, where it can reach stored boxes, freeze into a slick patch, or seep toward an interior wall. Leaves and road grit blow in and collect in the corners. If resealing hasn’t stopped these after a proper job, that’s a signal the door itself needs attention, and a service such as Schaumburg Garage Door Repair can check whether the panel, tracks, and floor are working against your new weatherstripping.
When resealing crosses over into an actual repair job
New seals are a maintenance task any homeowner can tackle. But when a fresh bottom strip still shows daylight, when the door rattles in its tracks, or when one corner sits visibly higher than the other, you’ve moved past sealing into alignment and hardware work. Bent tracks, worn rollers, a sagging section, or a slab that needs a threshold ramp all call for tools and judgment beyond a tube of caulk.
The draft along the floor is worth chasing down before it becomes a puddle, a nest, or a warped panel, because a door that seals well is usually a door that’s still hanging the way it should.