· by Michael Blair, Nashville's Garage Door
Stand in the garage with the door closed and the lights off on a sunny afternoon. If you can see a line of daylight along the floor, the bottom seal is not doing its job, and anything small enough to fit through that line is getting in. In late September and October that means blowing leaves, the first cold drafts, rain driven under the door in a storm, and mice looking for a warm place to spend the winter. The fix is usually simple, but the reasons the gap is there are not always the seal.
How the seal is held on
On most steel doors the bottom seal is a rubber or vinyl strip that slides into a two-channel aluminum retainer running the width of the bottom panel. The profile varies: a flat T-style, a looped bulb, a J-type. Each manufacturer’s retainer takes particular shapes, so a replacement has to match the channel, not just the width of the door. Bringing a piece of the old seal to the supplier, or measuring the slot, saves a second trip.
Wood doors and some older steel doors have no retainer; the seal is nailed or screwed straight to the bottom edge. On wood, that edge needs to be painted or sealed before a new strip goes on, because it is end grain sitting on a wet slab and it rots first.
When the seal is not the problem
A garage slab on Middle Tennessee clay moves. It settles, cracks, and often dips toward the center of the opening or along one side, so the floor is no longer a straight line. A door is straight. A new seal will close a small dip but it will not bridge a slab that has dropped more than its bulb can reach, and the gap comes back at the low spot.
Options there include a taller bulb seal, a threshold strip bonded to the slab that gives the door something to land on, or, for a badly broken apron, concrete repair. A threshold works well but it changes how water drains across the floor, and it can be a trip hazard or a snag for a mower, so it goes where the door closes and nowhere else.
- Daylight under the closed door at one end or across the middle
- Leaves or grit collecting just inside the door after wind
- Water on the floor after a storm, tracking in from the opening
- Rubber that is cracked, flattened or stiff to the touch
- Chewed notches, which usually mean mice have already been in
The mistake with the opener
When the door stops short of the floor, the tempting fix is to turn up the opener’s travel or force so it pushes harder into the slab. That is the wrong adjustment. The force setting is what lets the opener sense an obstruction and reverse, and cranking it up to crush a seal means it can also crush a bike, a pet or a leg.
The right order is: correct seal, then the down-travel limit set so the door just compresses it, then the reversal test in the opener’s manual, usually a board laid flat on the floor under the door. If the door does not reverse on it, the setting is wrong. A thicker new seal often needs exactly this adjustment, because the door now meets the floor a little sooner than it did.
Replacing it without getting hurt
Sliding a new strip into a retainer is a reasonable homeowner job. Raise the door to about waist height, clamp or lock it there so it cannot drift, unplug the opener, and pull the old strip out one side. A little dish soap on the new one helps it slide. Never work under a door that is held only by the opener or by your hand.
Leave the bottom brackets alone. On a torsion or extension spring door, the lift cables attach to the bottom corners and they are under spring tension all the time. Loosening those brackets to get at the retainer can release that tension suddenly. If the retainer itself is bent, split or corroded, that repair involves the bracket, and it is one for us rather than for a Saturday.