You can see daylight along the bottom of the door. It has been like that for a while, and it is a garage, so it has never quite made it to the top of the list.
It is the least expensive part on the whole door, it takes about half an hour, and it is doing more work than any other component you own.
What the seal is actually for
Four separate jobs, and most people only think about the first one.
- Water. A Texas thunderstorm can put an inch down in twenty minutes with a wind behind it. Driveways slope toward the garage more often than people realise.
- Air. An attached garage shares a wall and usually a ceiling with conditioned space. The gap under the door is a continuous opening into a hot attic-like space that your air conditioning is fighting all summer.
- Dust and debris. Everything blown along the driveway ends up in the garage, and then in the tracks, where it grinds.
- Everything that walks. Roaches, scorpions in some parts of the metro, mice, snakes. A gap of half an inch is a wide-open door to most of them.
The three parts, which people conflate
The bottom seal, or astragal. A rubber or vinyl extrusion that slides into a retainer along the bottom edge of the door. The common shapes are a U-section, a T-section and a bead. This is a consumable and it is the part that fails first.
The stop moulding. The vinyl-faced strip on the jambs and the header that the door closes against. Seals the sides and the top, and perishes in the sun exactly like the bottom seal does.
The threshold. A separate rubber ramp bonded to the floor that the door closes onto. Not standard, and it is the answer to an uneven slab or a driveway that slopes inward. Worth knowing about because it solves a problem the bottom seal cannot.
Why they fail here in particular
Ultraviolet and heat. The bottom seal is exposed to full sun on a south or west-facing garage and to a concrete driveway radiating heat back at it all afternoon.
The plasticisers that keep vinyl and rubber flexible migrate out under that treatment, and the material hardens. A hardened seal does not conform to the floor any more, and once it stops conforming it is decorative. Then it cracks, and in a hard freeze it becomes brittle and can split along its length in one cold night.
A DFW summer of consecutive triple-digit days is genuinely hard on these. Five to seven years is realistic on an exposed door; longer on one that is shaded.
How to check yours in a minute
Close the door and look along the bottom from inside with the lights off. Daylight anywhere is a gap. Pay particular attention to the corners, which is where wedges appear.
Then squeeze the seal between finger and thumb. New material is soft and springs back. Old material is hard and stays where you put it. That test tells you more than looking does, because a seal can look intact and have no give left in it at all.
If the gap is even across the whole width, that is a seal. If it is a wedge, wider at one end, the opening itself has moved, which in this metro usually means the slab, and the answer is a threshold rather than a taller seal.
Replacing it, honestly
This is one of the few garage door jobs that is genuinely reasonable for a homeowner. The door is closed, there is no spring tension involved at the seal itself, and the old extrusion slides out of its retainer and the new one slides in.
Three things worth knowing before starting. The retainer profile has to match the seal, and there are several incompatible shapes, so a photograph of the end of the retainer is what a supplier needs. Soapy water makes a new seal slide in a retainer that is otherwise almost impossible. And a retainer that is itself corroded or bent has to be replaced too, which is a different job.
The one part we would keep away from: the bottom brackets at each end are under full spring tension whenever the door is not fully open. The seal is fine to touch. The brackets are not.
The money question
No prices, but this is the cheapest meaningful item on a garage door and there is very little variation in it. Seal material is sold by the foot, thresholds are sold by the door width, and stop moulding is sold by the piece.
What changes the number is the retainer. Replacing a corroded aluminium retainer means working along the bottom of the door with it secured, which is real work. And on a door with no retainer at all, where the original seal was nailed on, fitting a modern retainer is an upgrade rather than a repair.
What not to buy
- Do not buy a taller seal to close a wedge. If one corner has a gap and the other does not, the opening is out of square and a taller seal will drag on one side and still gap on the other. That is a threshold job.
- Do not buy spray foam or caulk for the gap. The door has to move. Anything rigid gets torn off on the first cycle, and anything that stays traps water against the bottom of the door.
- Do not buy a seal without matching the retainer. The profiles are not interchangeable, and this is the single most common wasted purchase in this category.
- Do not buy a new door because it does not seal. Almost every sealing complaint is a consumable strip and a piece of stop moulding.
The short version
The cheapest part on the door is the one keeping out water, heat, dust and wildlife, and in this climate it hardens in about five years and then does nothing while still looking present. Squeeze it. If it does not spring back, it is finished.
It is also a job most people can do themselves in an afternoon, which is not a sentence you often read on a garage door company’s website. It is still true.
Garage Doors Pro Service · (469) 693-9000 · garagedoorsproservice.com
Serving Dallas, Plano, Frisco, McKinney and the DFW metro.
