The first cold evening of the season, you feel it before you see it: a thin stream of air sliding across the floor from under the front door.
It's one of the most common home and building complaints, and one of the cheapest to fix. The gap under a door is usually small, but it runs the full width of the opening, and air, dust, water, and insects all find it.
The solution is a door bottom or door sweep. This guide explains how they work, how to pick the right one, and how to install it so the seal actually lasts.
Why Air Gets Under a Door in the First Place
Doors need a small clearance at the bottom so they can swing freely over flooring, rugs, and thresholds. That clearance is necessary, but it's also an open path for air.
Over time the gap tends to get worse:
- Hinges settle and the door drops slightly.
- Old sweeps wear down, crack, or flatten.
- Thresholds wear unevenly or shift.
- Seasonal humidity makes wood doors swell and shrink.
A quick test: on a bright day, close the door and look at the bottom edge from inside. If you can see light, air is getting through.
Door Bottom vs. Door Sweep vs. Threshold
These terms get mixed up often, so it helps to separate them.
| Part | Where It Goes | What It Does |
|---|---|---|
| Door bottom / sweep | On the bottom edge of the door | Seals the gap between the door and the threshold |
| Threshold | On the floor, in the doorway | Gives the sweep a surface to seal against and bridges the floor |
| Weatherstripping | Along the sides and top of the frame | Seals the remaining edges of the door |
The best results come from using them together. A sweep seals against a good threshold, and the two parts do far more as a pair than either does alone.
What Kinds of Door Bottoms Are Available
Surface-mounted sweeps
These screw onto the face of the door, inside or outside. They are the easiest to install and the most common choice for homeowners.
Wraparound or U-shaped bottoms
These slip over the bottom edge of the door and are fastened from the sides. They hold up well on doors that see regular use.
Mortise or insert-style bottoms
These fit into a groove cut along the door edge. They look the cleanest, but they take more work to install.
How to Choose the Right One
- Measure the gap. Close the door and measure the space between the door bottom and the threshold at several points. Gaps are rarely even.
- Measure the door width. The sweep should cover the full width of the door, and you can trim it if it's too long.
- Check the door type. Wood, metal, and fiberglass doors all work with a sweep, but the fastening method may differ.
- Think about exposure. Exterior doors that face rain or wind need a durable, moisture-resistant material.
- Consider traffic. A busy storefront door needs a more durable sweep than a rarely used side entry.
How to Install a Door Sweep
Most surface-mounted sweeps go on in about 15 minutes with a drill and a screwdriver.
- Close the door and measure the width of the bottom edge.
- Cut the sweep to length with a hacksaw if needed, and file off any rough edges.
- Hold the sweep against the door so the flexible seal rests lightly on the threshold.
- Mark the screw holes, then pre-drill them to avoid splitting the door.
- Fasten the sweep, starting from the center and working to the ends.
- Open and close the door a few times. It should swing freely and the seal should touch the threshold evenly.
Tip: If the door drags on the floor, the sweep is set too low. Loosen the screws and raise it slightly. If you still see light, lower it a little. A good seal presses gently, not hard.
Common Mistakes to Avoid
- Setting the sweep too tight. It makes the door hard to open and wears the seal quickly.
- Ignoring a sagging door. If the gap is wider on one side, the real problem may be worn hinges, and a sweep alone won't fix it.
- Skipping the threshold. A sweep sealing against bare, uneven flooring never seals completely.
- Forgetting double doors. If you have a pair, the center joint leaks too. A T-astragal seals that gap.
- Waiting too long to replace. A cracked or flattened sweep no longer seals. Check it at least once a year.
Beyond Drafts: Other Benefits of a Good Door Bottom
- Helps keep out dust, leaves, and debris.
- Reduces the chance of insects and small pests entering.
- Limits water getting under the door during rain.
- Cuts down on outside noise.
- Helps your heating and cooling system hold temperature more easily.
FAQ
What is the difference between a door sweep and a door bottom?
The terms are often used interchangeably. Both describe a strip on the bottom edge of the door that seals the gap against the threshold or floor.
How big of a gap can a door sweep seal?
It depends on the product. Measure your gap and check the product's size range before buying. If the gap is very large, the door may need adjusting or a taller threshold.
Can I install a door sweep myself?
Yes. Most surface-mounted sweeps need only a tape measure, a drill, a screwdriver, and a hacksaw to trim the length.
Should the sweep go on the inside or outside of the door?
On most exterior doors, the inside is common because it keeps the sweep out of the weather. Some styles are made for the outside or wrap around the door. Choose based on your door type and exposure.
How often should I replace a door sweep?
Check it once a year. Replace it when the seal is cracked, flattened, torn, or no longer touches the threshold evenly.
Will a door sweep stop pests?
It closes one of the most common entry points for insects and small pests. For best results, also seal the sides and top of the door and check the threshold.
Have more questions? Visit our full FAQ page.
Final Thoughts: Small Gap, Big Difference
The space under a door is easy to ignore until the weather turns. A good door bottom, a solid threshold, and a door that hangs straight add up to an opening that stays comfortable, clean, and quiet.
If you can see light under your door, or feel air moving across the floor, you already know what to fix.