Why is there a gap at the top of my garage door?

A top gap is a different failure from a bottom or side gap

The advice that fixes a gap under the door will not fix a gap above it, because the parts involved are different. A bottom gap is about the door meeting the floor, so it comes down to the bottom seal, the concrete, and whether the door closes square. A side gap is about the door meeting the jambs, the vertical framing on either side, so it comes down to level, vertical track, and side stop molding.

A top gap is about the door meeting the header, the framing across the top of the opening. DASMA, the door manufacturers' association, defines the door header as "the upper part of a door frame, consisting of the head jamb, head casing, stop and trim." Three parts control whether your top section presses against it: the top seal, the top fixtures, and how far the door travels before it stops. None of those are on the bottom or side gap checklist, which is why people buy a bottom seal, install it, and still see daylight above the door.

There are five realistic causes. Two are cheap. Three are not.

First, read the shape of the gap

Turn off the garage lights in daylight, close the door fully, and stand inside looking at the strip above the top section. The shape of the light tells you which cause you have before you touch anything.

• An even strip, the same width all the way across. The top seal or the top fixtures. Causes 1 and 2 below.
• Widest in the middle, closing to nothing at both top corners. The top section is bowed. Cause 4.
• Wider at one end than the other. The door is hanging out of level, which is a track and cable issue, not a top issue. Our page on a garage door gap on one side covers that.
• A gap at the top and the bottom seal is not touching the floor either. The door is not finishing its travel. Cause 3, and it is the one people misdiagnose most.

Measure the width with a tape while you are there. Under about a quarter inch is normal on many doors and is what the seal exists to close. An inch of daylight is a hardware problem.

Cause 1: the top seal is worn, missing, or the wrong profile

This is the cheap one, and it is the right answer more often than not. DASMA defines the top seal as "weatherstripping which fastens to the top of the door to seal the door along the top of the opening." A related part, the header seal, mounts on the header itself rather than the door.

Vinyl and rubber both harden and shrink with age and with Colorado's temperature swings, and a flap that has gone stiff no longer bends against the door face. Look for a strip that is cracked, flattened, pulled loose at one end, or simply absent because nobody installed one.

The other version of this is the stop molding, the trim nailed to the outside of the frame. DASMA describes its job directly: it "serves to seal the perimeter of the door against weather and light infiltration; usually nailed to the jamb, outside the door." If the stop molding across the top sits too far off the door face, no seal will bridge it, and the molding needs to be repositioned rather than the seal replaced.

Verdict: a genuine do it yourself job. The seal is inexpensive and installs with nails or screws. Note that seals are frequently sold separately from the door, as Amarr's installation instructions state, so a builder grade door may never have had one.

Cause 2: the top fixtures are out of adjustment

If the seal is sound but the top of the door still stands away from the header, the top fixtures are the next suspect. A top fixture, in DASMA's terms, is "a bracket for positioning the top guide roller on the top section of a door." You will also see it called a top roller bracket or top carrier. There is one at each upper corner.

The part that matters is that the fixture is adjustable. It has a slide that sets how far the top roller sits out from the door face, which controls how firmly the top section is pulled toward the opening when the door closes. Amarr's installation instructions describe the setting step exactly: "With the door in the closed position, tighten the slide on the Top Fixture by pushing the top section tight against the opening and lightly pulling the top slide toward the inside of the garage."

If that slide was never set correctly, or the nuts loosened over years of cycling, the top section rides too far into the track and leans away from the header. The result is an even gap along the whole top edge, which is why this looks identical to a seal problem from the driveway.

Verdict: borderline. The adjustment itself is two nuts per side. The risk is that the top fixture is fastened to the top section and sits near the counterbalance hardware, and an over adjusted fixture can pull the top rollers out of the track. If you are not confident, this is a short service call rather than a project.

Cause 3: the opener stops the door short of full close

Check this before you buy any parts, because it costs nothing. If you see a gap at the top and the bottom seal is not compressed against the floor, the door is not completing its travel. The whole door is sitting high, which leaves the top section still partly in the curved part of the track. That tips its top edge inward, away from the header, and opens a wedge shaped gap at the top.

The fastest confirmation takes thirty seconds. Pull the red emergency release cord with the door closed, then lower the door the last inch by hand. If the gap closes and the bottom seal meets the concrete, the door and its hardware are fine and the opener's limit setting is wrong.

The fix is the down travel limit. On openers with manual screws, Chamberlain's instructions are specific: "To increase the down travel, turn the DOWN limit adjustment screw counterclockwise. One turn equals 2 inches (5 cm) of travel." Move it a quarter turn at a time and test between each. Chamberlain is emphatic about the last step: "After you do ANY adjustments, the safety reversal system MUST be tested." Our page on adjusting travel limits and force settings walks through the full procedure and the force settings you should not touch.

Verdict: do it yourself, with the reversal test as a mandatory finish. Never increase the down force to close a gap. That defeats the protection that stops the door on an obstruction.

Cause 4: the top section is bowed

A gap that is widest in the middle and disappears at both corners means the top section itself is curved, not the hardware. DASMA calls this thermal bowing, and its technical data sheet on the subject is clear that it "is an inherent characteristic on garage doors with insulated bonded core sections and is not considered a product defect."

The mechanism is simple. On an insulated door, the outer steel skin and the inner skin are bonded to a foam core. When one side is much warmer, DASMA explains, "the warmer skin will grow relative to the cooler skin and cause the door to bow in the direction of the warmer skin." A dark door in direct sun with a cool garage behind it bows outward. A heated garage in a Colorado winter can bow a door inward instead. Bigger doors bow more, and DASMA notes that without reinforcement the bow on a 20 foot wide door "could exceed several inches."

The tell is that it comes and goes. Thermal bow flattens out when the temperature evens up, usually overnight, so check the same gap in the early morning. If it has closed, that is thermal bow and the door is behaving normally. If the section is bowed at every hour and in every season, it is permanent, which points to delamination or a section that needs a strut, the horizontal reinforcing brace fitted across the back of a section.

Verdict: not a seal problem, and not a fix. Adding a strut is a technician job, and a delaminated section may be a warranty claim with the door manufacturer.

Cause 5: the header or the opening has settled

If nothing above fits, look at the opening rather than the door. A square opening is an installation requirement, not an assumption. Amarr's instructions state that "the jambs must be plumb and the header level for a square opening," and the final check calls for roughly three eighths of an inch of clearance between the door and the track along the whole assembly.

Older garages move. A header can sag over a wide opening, a garage slab can settle and rotate the frame, and either leaves the door square while the opening is not. The result is a gap that tapers along the top and that no amount of seal or fixture adjustment will close, because you are sealing against a line that is no longer straight.

Confirm it with a level held against the underside of the header, not against the door. If the header reads out of level and the door reads true, the framing is the problem.

Verdict: structural, and outside garage door work. This is a carpenter or a contractor. A door company can shim the tracks and fit an oversized seal to hide a small amount, but that treats the symptom.

What to do yourself, and what to leave alone

Safe to handle: replacing the top seal, repositioning stop molding, adjusting the down travel limit and retesting the reversal, and checking the header with a level.

Leave alone: anything attached to the springs, cables, or the counterbalance hardware above the door. DASMA's position is that "all repairs and adjustments must be performed by a trained door systems technician using proper tools and instructions," and its guidance for inspectors is to look at parts under spring tension but not touch them. Top fixture adjustment sits close to that hardware, which is the one item on this page worth handing over if you have any doubt.

Work through the list in order. Most top gaps end at cause 1 or cause 3, and both are an afternoon and a small part rather than a repair bill.