What to Do About That Under-Door Draft in Your Building

If you’ve ever walked into a room and felt a sudden chill around your ankles, you know the problem: the dreaded under-door draft. It seems small, just a sliver of space under the door, but it adds up. Cold air slips in, warm air leaks out, and before long, you’re dealing with higher bills and uncomfortable tenants.

So let’s talk about why drafts happen, how you can spot them, and the real-world fixes that actually work.

Think about it like this: even a gap as small as one-eighth of an inch around a door can let through as much air as a window that’s half open. That’s not just a nuisance; it’s wasted money. According to the U.S. Department of Energy, uncontrolled air leaks in commercial buildings account for nearly one-third of heating and cooling loss every year.

And when you look at the big picture, the costs are serious. The Energy Information Administration estimated that commercial buildings spent $142 billion on energy in a single year, with insulation/energy loss being one of the top culprits.

It starts with a walk-through. Put your hand along the bottom and sides of your doors. If you feel air movement, you’ve got air leaks. Another trick: slide a sheet of paper under the door. If it moves easily, the gap is too wide.

You might also see daylight at the threshold, a sure sign that a door sweep or gasket isn’t doing its job. Sometimes it’s not just the bottom of the door. Shrinking seals, cracked frames, or worn weatherstripping at the sides can all reopen gaps you thought were sealed.

Most of the time, drafts start under the door. A door sweep is the simplest fix. It’s just a strip that attaches along the bottom and seals against the floor.

If you’ve got a smooth threshold, a vinyl door sweep works well. For rough or uneven floors, a brush door sweep is better. Either way, it stops air leaks right where they happen most.

That’s where a gasket comes in. It lines the jamb and head of the frame and compresses when the door closes. Over time, gaskets can harden, shrink, or even peel away. Once that happens, the door can’t hold a seal anymore. 

When replacing them, your best options are:

• Silicone gaskets: durable, long-lasting, and flexible even in extreme temperatures.

• Foam gaskets: quick and inexpensive, but they wear out faster.

• Magnetic gaskets are often used in cooler or freezer doors, but are also useful in some commercial setups.

Choosing the right gasket depends on the amount of daily use your doors experience and the type of environment they’re in.

Here’s the thing: a single fix rarely covers every gap. A full seal usually means combining a door sweep, a gasket, and proper weatherstripping.

Weatherstripping comes in a few forms:

• Tape: easy and affordable, but not durable.

• V-strips: typically made of metal, strong enough for high-traffic doors.

• Gaskets: thicker, better for irregular gaps.

• Sweeps: best for the bottom edge of the door.

The payoff? Better comfort for tenants, lower utility bills, and less strain on your HVAC system.

Sometimes a draft isn’t just about the seals. A warped frame or sagging leaf will keep any fix from working. If you’ve replaced the door sweep, updated the gasket, and added new weatherstripping, and you still feel air leaks, the issue might be structural.

At that point, it’s better to repair/replace the door than keep patching it. Yes, it costs more upfront, but it saves money over time because you’re not wasting energy every month.

You don’t have to live with an under-door draft. Start by sealing gaps with a door sweep, updating old gaskets, and adding weatherstripping where needed. Keep up with maintenance, and don’t be afraid to repair/replace the door if the frame itself is the problem.

For more ideas, you can read our guide on measuring for a new commercial door, which explains how to get the sizing right if replacement is on your list. Alternatively, if you’d rather discuss it further, you can reach out to CDF Distributors. Our team works closely with general contractors, facility managers, and business owners every day, and we’ll provide you with the exact guidance you need to stop drafts for good.