Quick answer: A draught under a closed door usually comes from an incorrect threshold gap, worn door sweep, damaged weatherstripping, loose threshold, poor alignment or an unsealed frame-to-floor joint. First clean the sill, close and lock the door normally, then check whether the gap is even from hinge side to latch side. Replace only compatible seals and confirm that the door can still close, latch and drain correctly.
A strip of light or cool air at floor level is easy to notice, but the source is not always the same. Sometimes the bottom seal is worn. In other cases, the door has sagged, the threshold has shifted or air is travelling through the installation joint rather than directly beneath the leaf. The safest repair begins with diagnosis, not with adding the thickest foam strip you can find.
Contents
- How to test a door-bottom draught
- Six common causes
- Safe repair options
- Repairs that can create new problems
- When professional help is needed
- Frequently asked questions
How to check where the draught is entering
Perform the check with the door closed and latched as it would be in normal use. Turn off nearby fans temporarily so they do not confuse the result. Use the back of your hand or a light tissue along the bottom edge, both lower corners and the frame-to-floor junction. Do not use a candle, incense stick or any other flame.
Observe the pattern:
- Even air movement across the full width: the sweep may be worn, missing or too high.
- A larger gap at one bottom corner: the door may be sagging or the frame may be out of square.
- Air at the frame-to-floor joint: the installation perimeter may need assessment rather than a new sweep.
- Draught only before the latch engages: compression may depend on correct locking.
- Wetness or staining as well as air: investigate water management, sill condition and exterior exposure before sealing.
A thin, even operating clearance is normal. The goal is not to make the door rub the floor; it is to create the designed contact between the door-bottom seal and threshold while preserving reliable closing and latching.
Six causes of a door draught at the bottom
1. The door sweep or bottom seal is worn
A sweep can split, flatten, harden or lose sections after repeated contact with the sill. Examine the seal with the door open and supported. Look for polished patches, tears and sections that no longer project evenly. Some sweeps slide into a channel; others are screwed or bonded in place. Record the profile and dimensions before ordering a replacement.
2. The threshold is loose, low or uneven
A threshold may have adjustable components, but the correct procedure depends on the product. If it rocks, has exposed fasteners or varies noticeably in height, do not simply build it up with layers of tape. A loose threshold can affect both air sealing and water management. Adjustment should leave a consistent seal without making the door difficult to operate.
3. The door has dropped on its hinges
Door sag often produces an uneven gap: larger below the latch side, tighter at the opposite top corner, or accompanied by rubbing elsewhere. Check whether hinge screws sit flush and whether a hinge leaf moves while the door is gently operated. Tightening an accessible loose compatible screw may help, but a stripped fixing, bent hinge or heavy glazed leaf needs professional repair.
4. Side weatherstripping does not reach the bottom corners
Air often bypasses the centre of a good sweep and enters through a lower corner where the side gasket, bottom seal and threshold meet. Look for a missing end piece, shrunk gasket or folded corner. Use only the intended corner pad or compatible seal; stuffing the space with tissue or excess foam can hold the door away from the frame.
5. The frame-to-floor joint leaks
The door leaf may seal correctly while air moves through a crack under the threshold or around the frame. A draught felt at trim edges, together with a clean door-bottom contact line, points toward the installation joint. This often requires removal of trim or controlled sealing by an installer so the appropriate layer is addressed without trapping water.
6. The replacement seal is the wrong size
Thicker is not always better. An oversized seal can prevent the latch from engaging, place excess force on hinges, make the handle difficult to operate or leave a new corner gap. An undersized seal will not make continuous contact. Match the original design, measure the channel and test the door after installation.
Six safe ways to reduce a draught under the door
- Clean the threshold and seal contact line. Vacuum grit, then wipe with a damp cloth and mild detergent. Dry the area before testing.
- Close and lock the door correctly. Confirm that the latch or multipoint lock engages without unusual force. Compression seals work only when the door reaches its intended position.
- Tighten only clearly loose accessible fasteners. Support the door and use the correct hand tool. Stop if the fixing spins, the hinge moves in the frame or the leaf is heavy.
- Replace a damaged sweep with a compatible profile. Match its fixing method, width and projection. Trim only according to the manufacturer’s instructions.
- Re-seat an obviously displaced removable gasket. Do not stretch it. If it has shrunk, hardened or torn, obtain the correct replacement.
- Have the threshold or installation joint assessed. Choose this route when the gap is uneven, the sill is loose, water is present or the draught comes from beneath the frame.
The U.S. Department of Energy’s weatherstripping guidance describes the intended outcome as reducing infiltration while maintaining proper door operation. That balance matters: a door that is airtight only when slammed, lifted or forced is not correctly repaired.
| Symptom | Likely area to inspect | Best next step |
|---|---|---|
| Even gap under entire door | Sweep and threshold height | Confirm compatible seal and adjustment procedure |
| Gap wider at one corner | Hinges and frame alignment | Arrange alignment assessment |
| Air at trim or floor joint | Perimeter installation seal | Inspect the stationary joint before caulking |
| Door will not latch after new seal | Seal thickness or position | Stop forcing; fit the correct profile |
| Air plus rainwater | Sill, threshold and drainage | Request water-management inspection |
What should you avoid?
- Do not seal over drain slots or weep paths.
- Do not stack several adhesive foam strips on top of the existing gasket.
- Do not raise a loose threshold with improvised wedges.
- Do not plane, grind or cut the door before checking alignment.
- Do not spray oily lubricant onto a threshold or seal; it attracts dirt and may create a slip hazard.
- Do not modify fire-rated doors, smoke seals or self-closing hardware without an appropriately qualified specialist.
When to call a door specialist
Professional help is appropriate when the door is glazed, unusually heavy, fire-rated or fitted with multipoint locking; when hinges or the frame move; when the sill is loose or corroded; or when air leakage is accompanied by water. A specialist can check the entire closing geometry rather than replacing one visible seal and hoping it compensates for a different defect.
Before the visit, photograph the full door from inside, both bottom corners, the sweep profile and the threshold. Note whether the draught changes when the door is locked and whether it occurs during specific wind directions. To explore replacement configurations, see Forge Windows products. For help evaluating an existing entrance, contact Forge Windows with the photos and measurements.
Frequently asked questions
Can I use a door snake as a permanent fix?
A removable draught stopper may improve comfort temporarily on the inside, but it does not correct a damaged seal, loose threshold or alignment problem. It should never interfere with emergency exit or door operation.
How much gap should there be under a door?
There is no universal measurement. The correct clearance depends on the door system, threshold, floor finish, drainage design and any fire or accessibility requirements. Follow the product specification rather than a generic number.
Why is the draught worse after I replaced the sweep?
The replacement may be too short, installed backwards, unevenly trimmed or incompatible with the threshold. It may also be hiding an alignment problem. Compare contact across the full width and confirm the intended profile.
Should the bottom seal touch the threshold?
Many systems are designed for controlled, continuous contact, but the amount and type of contact vary. It should not fold severely, drag excessively or prevent latching.
