Gap Down the Side of the Garage Door

The mildest version and the most common. The flap on the stop molding is meant to lie against the face of the door with a slight bend in it — a set that it holds through thousands of cycles. Once the vinyl loses flexibility, it straightens out and stands proud of the door instead of leaning on it.

You end up with a seal that is present, unbroken, and touching nothing. Light passes between the flap and the door face along the full height. The tell is that the gap is thin, absolutely even, and the flap looks like it's pointing at the door rather than resting on it.

Vertical seals fail this way faster on whichever side takes the afternoon sun, so it's normal to find one side fine and the other side done on the same door.

How you can tell: The flap doesn't spring back when you push it toward the door, and there's a visible shadow line between it and the door face along its whole height.

A geometry problem rather than a wear problem, and you can spot it because the gap is even down both sides at once.

The classic version is a replacement door fitted into an opening whose trim was left alone. Doors vary in thickness, in how far the end stiles stand out, and in how far they run from the jamb. Set the same trim in front of a slightly different door and the flap ends up short of the face by a sixteenth or an eighth of an inch — enough to see light through and enough for grit to blow past.

The other version is simply a careless original install. Nothing has failed; it was never right.

How you can tell: Both sides show a similar even gap, the seal itself is soft and in good condition, and the flap ends short of the door face rather than resting on it.

Stop molding is fastened into the wood jamb, and jambs on a Phoenix-area garage lead a hard life. Sun on the outside face, big daily temperature swings, and wood that has dried well past its original moisture content. Nails and screws lose their grip in dry wood, and the trim starts to move.

What accelerates it is impact from the door itself. A door that comes down hard — a worn counterbalance, a fast close, a slam — transmits that shock into the frame. Do it a few thousand times and the trim near the bottom of the run works loose first, which is why the gap so often starts as a widening at the bottom corner and grows upward.

The same loosening affects the track brackets bolted to that jamb, which is why this cause sits on the boundary between a trim job and a door job.

How you can tell: You can move the trim by hand, or see a shadow gap between the molding and the jamb. Fastener heads may be standing proud or backed out.

When the gap wedges — narrow at one end, wide at the other — the door is no longer parallel to the jamb. The usual reason is that one vertical track is no longer where it was set.

Vertical tracks are bolted to brackets on the jamb, typically two or three per side, and those bolts sit in slotted holes so the installer can set the door's clearance. Slots that allow adjustment also allow drift. A bracket that has loosened lets the top of the track lean out or in, and the door follows the track, so the top of the door ends up further from the jamb than the bottom.

The other route to the same symptom is impact. A vehicle mirror, a bumper, a ladder — anything that moves a track sideways puts the door out of parallel from that day on, and the gap is often the first thing anybody notices.

How you can tell: The gap is clearly tapered, and looking up the vertical track you can see it isn't plumb, or a bracket bolt is loose in its slot.

The version to take seriously. A gap that widens toward the bottom, with one bottom corner sitting lower than the other, means the door isn't level in the opening — and a door only hangs level as long as both lift cables are carrying it equally.

If one cable has slipped, spooled unevenly on its drum, or come off entirely, one side of the door sits low. The bottom corner on that side moves away from the jamb and a wedge of light appears. Rollers on that side are now loaded at an angle, and every cycle from here makes it worse. That's the state immediately before a door comes off its track, which is why the door's level matters far more than the gap does.

There's a second version that's specific to this valley. Expansive soil and post-tension slabs mean garage floors around Mesa, Queen Creek and Gold Canyon genuinely move. When the slab drops at one corner, the framing and the jamb go with it, and the door — which hasn't moved at all — ends up out of parallel with an opening that has. That one is diagnosed differently and it has its own page.

How you can tell: Wedge-shaped gap wider at the bottom, one corner of the door visibly lower than the other against the slab, and often a slack lift cable or a cable spooled unevenly on its drum.

An intermittent version that confuses people, because with the door closed everything measures correctly.

A door is held laterally by its rollers sitting in the tracks, with a small amount of clearance so it can move freely. When that clearance grows — worn roller wheels, bent stems, a track set slightly too wide, or hinge play from loose fasteners — the door has room to shuffle sideways as it travels. It ends up closing a quarter inch to one side of where it started, which shows as a gap on one edge that wasn't there yesterday and may not be there tomorrow.

The associated sounds are useful. A door that shifts as it runs usually knocks or clatters at the point where it takes up the slack, and the noise is repeatable at the same place in the travel.

How you can tell: The gap size changes between cycles, and the door doesn't come to rest in exactly the same place each time. Often a knock or clunk partway through travel.

This one gets almost no coverage and it explains a symptom that sends people down completely the wrong path.

An insulated door is a sandwich: a steel skin outside, a steel skin inside, and foam bonded between them. In summer those two skins sit at very different temperatures, and materials grow when they get hot. DASMA covers this in Technical Data Sheet #185 and is unambiguous that it's normal: thermal bowing “is an inherent characteristic on garage doors with insulated bonded core sections and is not considered a product defect.” The warmer skin grows relative to the cooler one, and the door bows toward the warmer skin.

Now apply that here. Hot outside, cooler or air-conditioned inside means the outer skin is the warm one, so the door bows outward. And DASMA names the field symptom of an outward bow precisely: “top section rubbing on the top of the garage door opening header.” The version that opens a gap at the top — “a gap between the top section and the top of the opening” — is the inward bow, which is the cold-outside, heated-garage case. That's a Minnesota problem, not ours.

So the practical rule for a Valley door: if you have a gap along the top, don't blame thermal bowing — go back to the trim and seal causes above. But if your door starts scraping the header on hot afternoons and stops in the cooler months, that's very likely thermal bowing, and no amount of new rubber will touch it.

DASMA also lists what makes it worse, and the list reads like a description of a Phoenix garage. A bigger door bows more — an unreinforced 20-foot door “could exceed several inches.” A darker door bows more: DASMA's own example is that “a brown, insulated garage door facing the sun on a hot day with an air-conditioned garage or warehouse space will have more thermal bowing than an equivalent white garage door in the same application.” Thermally-broken construction bows more, because the break is doing its job and keeping the two skins at different temperatures. Aluminum and plastic skins expand more than steel. And orientation matters: “a south facing door in direct sunlight will be more likely to experience thermal bowing than a north facing door out of direct sunlight.”

The remedy is structural, not a seal. DASMA's answer is door reinforcement — “the application of horizontal struts across the back of the garage door,” with the size and number varying by door. Extreme cases need more than that, and other approaches depend on whether the track assembly or the jamb and header seal are adjustable on your particular door. DASMA's closing instruction is to contact the product manufacturer for their recommendation, which is what we'd do too.

How you can tell: The top of the door contacts or scrapes the header on hot afternoons and runs clear on cool mornings or in winter. Worse on a dark, large, south- or west-facing insulated door with a cooled garage behind it.