Why is there a gap on one side of my garage door when it's closed?

A gap along one side of a fully closed garage door is more than a weatherproofing problem. It lets in cold air, dust, pests, and moisture, and in Colorado it is especially noticeable in winter when wind drives snow horizontally. Pinpointing whether the gap comes from the door, the track, the molding, or the floor determines the right fix.

Check whether the door itself is level

Start by measuring the gap at the top and bottom of the problem side. If the gap is even from top to bottom, the door is parallel to the opening but offset horizontally from the stop molding. If the gap is wider at the bottom than the top (or vice versa), the door is tilted at an angle within the opening.

An even gap from top to bottom points to the stop molding or the track position being shifted. An angled gap usually means the door itself is not level, often because of a spring or cable imbalance.

A simple way to check door levelness: with the door fully closed, place a level on the bottom edge of the door. If the bubble is not centered, the door is tilted. Check the track on both sides with a level as well.

Gap pattern	Likely cause	Fix
Even gap from top to bottom on one side	Stop molding shifted or track offset	Adjust molding or track
Gap wider at bottom	Door tilted (low on that side)	Cable or spring inspection
Gap wider at top	Door tilted (high on that side)	Cable or track check
Gap appears in cold weather only	Seal stiffening and contracting	Replace weather seal

Stop molding problems

Stop molding is the strip of wood or composite attached to the inside of the garage door frame that the door closes against. It seals the gap between the door edge and the rough framing. If the stop molding on one side has shifted outward, bowed, or was never correctly positioned, the door closes against it unevenly and a gap appears on the outside edge.

Run your hand along the inside of the molding on the gap side. Is it tight against the door edge when the door is closed? Is it attached firmly to the frame, or does it flex? A molding strip that has pulled away from the frame due to humidity changes, nail backing failure, or settling can be re-nailed and repositioned. Add a foam backer rod or replace the molding if the existing piece is warped.

In Colorado, the low humidity means wood products installed at the factory (in wetter climates) sometimes shrink after installation in Denver homes. This can cause slight gaps in molding joints that let air and light through. A bead of paintable exterior caulk along the seam addresses this.

Track alignment and its effect on gaps

The vertical track on each side channels the door as it travels. If one track is mounted slightly farther from the opening edge than the other, the door will be positioned slightly inside the opening on one side and outside on the other. This shows up as a gap on the outward-shifted side and a tight fit on the inward side.

To check: measure the distance from the inside face of each vertical track to the edge of the rough door opening. Both sides should be equal. A difference of more than 1/4 inch is enough to cause a visible side gap.

Track repositioning involves loosening the bracket lag screws, shifting the track, and re-securing it. The track must remain plumb after the shift, so check it with a level from top to bottom before tightening.

Uneven or settled concrete floor

An uneven concrete floor is a frequent cause of side gaps in older Denver garages. As the garage floor settles or cracks over time, the overall plane of the floor can tilt slightly. The door's bottom seal follows the top edge of the door's travel, not the floor surface. If the floor is lower on one side, a gap appears between the bottom of the door and the floor on the low side.

This is not technically a side gap, but homeowners sometimes perceive it as one because the gap runs along the corner between the side and the bottom. A bottom sweep or a replacement threshold seal (a rubber strip bonded to the concrete) addresses the floor-level gap without requiring track work. Threshold seals are available in lengths up to 20 feet and are cut to fit.

Replacing side weather seals and verifying the fix

Even when the door and track are correctly positioned, side weather seals on the stop molding may be missing or degraded. Side weather seals are flexible rubber or vinyl strips that compress against the door face when it closes, filling small gaps.

On Front Range homes, side seals take a beating from UV exposure, dry air, and temperature swings. A seal that looks intact in summer may be cracked and stiff by February. Replacement seals are inexpensive (under $20 per strip) and install with small screws or staples. Replace them if you can see daylight around the door edge when it is closed.

After any repair to stop molding, track position, or weather seals, run the door through several cycles and check the gap from both inside and outside. Hold a flashlight against the gap from the outside while someone watches from the inside. If you see light at any point, the seal is not complete at that location.

A piece of weather stripping that closes the gap visually may still allow air infiltration if it is not compressed tightly. Press your hand along the door edges on a windy day to feel for drafts.

For homes with attached garages, a tight side seal reduces sound transmission from traffic and lawn equipment. In Colorado, where temperature differentials between inside and outside the garage can exceed 50 degrees on winter mornings, a sealed garage door is a real energy improvement. Gaps that seem minor in summer become significant heat loss channels in winter. Addressing side gaps alongside bottom seal replacement gives you a fully sealed perimeter.

Pest entry is another reason to take side gaps seriously. Mice can pass through openings as small as a quarter inch. A gap along the door side, even one that is not visible as daylight, is enough for rodent entry. Front Range homeowners often notice an uptick in mouse activity in fall as temperatures drop and animals look for shelter. Sealing the door perimeter in September is a reasonable prevention step.

If you are unsure whether the gap is from the door, the track, the molding, or the floor, G Brothers can diagnose the source on a service visit. Knowing the cause before buying weather seal materials or attempting adjustments saves both time and money. Most side-gap issues are resolved in a single visit, and the repair cost is usually far less than a larger mechanical issue like a spring or cable replacement. If the gap is caused by a track or spring problem, the technician will catch that on the same visit and can quote the full repair at once.

G Brothers Garage Doors serves the Denver metro and Front Range with free estimates, same-day service on weather sealing and track adjustments, and 24/7 emergency response. Licensed and insured.