Why is there a gap under my closed garage door?

Finding the cause is mostly a matter of looking at where and how the daylight shows. A gap straight across is a different problem than a gap on one corner.

What causes a gap under the garage door

Read the shape of the gap to point at the cause:

• An even gap all the way across. Almost always the bottom seal: worn flat, cracked, shrunk in the cold, or too short for the door. This is the most common cause and the easiest fix.
• A gap that grows toward one corner. The door is sitting crooked. That points to a cable, spring, or track problem on the low side, not the seal.
• A gap only in the middle. Often a settled or low spot in the concrete, or a wide door that sags slightly between the ends.
• A gap that appeared after a cold snap. Rubber stiffens and shrinks in deep cold, so an old seal can pull back from the floor in winter.

Fixing a gap from a bad seal

If the gap is even across and the rubber looks worn, cracked, or hard, a new bottom seal closes it. Match the new seal's profile to your retainer and, if the floor is slightly low, step up to a taller seal that bridges the gap. Our step-by-step on bottom seal replacement walks through it.

For an uneven floor, a few options work depending on how big the low spot is:

• A taller or U-shaped bottom seal to span a shallow dip.
• A threshold seal glued to the floor itself, which is good for water and a sloped apron.
• Both together for a stubborn gap, the seal on the door meeting the threshold on the floor.

A threshold seal is also the better choice if water runs in during Front Range thunderstorms, since it builds a small dam at the opening.

When the gap means a door problem

Sometimes the seal is fine and the door is the issue. A gap that is worse on one side usually means the door is not hanging level. Causes include a stretched or broken cable, a tired spring on one side, or a bent or misaligned track. The door closes until one corner hits the floor while the other still floats, leaving a wedge of daylight.

This is more than a draft. A crooked door wears rollers and tracks faster and can eventually jump off track. If a new seal does not fix the gap, or the gap is clearly one-sided, treat it as a balance or hardware issue and have it checked. These are also the kinds of warning signs worth catching early.

Why closing the gap matters in Colorado

A gap under the door is not just uncomfortable. It lets heated air escape and cold air in, which runs up the bill on an attached garage. It invites mice, spiders, and leaves. And it lets snowmelt run under the door, where it can refreeze and bond the seal to the slab so the door freezes to the ground. Sealing the bottom edge is one of the cheapest comfort and pest upgrades you can make here.

When to call a pro

A worn seal on an even gap is a fair DIY fix. Call a tech when the gap is one-sided, a new seal does not close it, or you suspect a cable, spring, or track problem behind it, since those involve the door's tension and balance.

Our crews across Denver, Lakewood, and the Front Range can find the real cause, replace seals or thresholds, and correct a door that is hanging crooked, all with flat-rate pricing. To get the gap under your door closed for good, call our 24/7 line at (303) 937-4477.