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DRAUGHTS & SEALS

Gap Under Door

A gap under a door may be intentional for ventilation, but excessive gaps cause draughts, noise and light leakage.

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Do not block required ventilation or drainage

Some gaps, vents and drainage slots are intentional. Fire doors, external doors and emergency windows may also have specific sealing requirements.

MOST LIKELY CAUSES

Start with the exact air or water path

Door trimmed too high Previous flooring or trimming left excess clearance.
Missing bottom seal No brush, blade or drop seal is fitted.
Low threshold The floor transition does not meet the door.
Uneven floor The gap varies across the width.
◫ Symptom variations Match the draught, gap or seal pattern. ⌄
  • Light visible below door
  • Cold air at floor level
  • Noise passes easily
  • Gap is larger on one side
  • Door was cut after new flooring
✓ Quick checks Safe checks before replacing seals. ⌄
  1. Measure the gap across the full width.
  2. Identify whether ventilation clearance is required.
  3. Check floor level and threshold.
  4. Confirm the door still swings freely.
  5. Check fire-door or accessibility requirements.
Important: Find the exact leak path first. Replacing the wrong seal can make closing harder without fixing the fault.
1 Step 1 — Measure and identify requirements Make the smallest safe correction and retest. ⌄

Do not block required ventilation or fire-door clearances.

2 Step 2 — Choose the correct seal type Make the smallest safe correction and retest. ⌄

Use brush, blade, threshold or automatic drop seal as appropriate.

3 Step 3 — Fit and test Make the smallest safe correction and retest. ⌄

Ensure the door closes freely and the seal contacts evenly.

⌁ Why the problem happens How compression, alignment and weathering affect sealing. ⌄

Door-bottom solutions must balance sealing, movement and ventilation. The wrong product can drag, jam or block airflow.

⌘ Advanced checks Further diagnosis for persistent sealing faults. ⌄
  1. Check floor variation.
  2. Assess threshold drainage on external doors.
  3. Review acoustic requirements.
  4. Check smoke-seal requirements.
  5. Measure door undercut against regulations.
◇ Tools and information needed Useful items for accurate checks. ⌄
  • Tape measure
  • Screwdriver
  • Saw or snips for seal
  • Drill
  • Spirit level
▣ Parts or improvements that may help Common sealing products linked to this problem. ⌄
  • Brush strip
  • Rubber blade seal
  • Automatic drop seal
  • Threshold bar
  • Combined threshold system
! When to call a professional Conditions that should end basic DIY diagnosis. ⌄
  • The door is a fire or smoke door.
  • The gap is needed for ventilation.
  • The floor is badly uneven.
  • An external threshold leaks water.
  • Accessibility requirements apply.
? Frequently asked questions Common draught and seal questions. ⌄

Should every gap be sealed?

No. Some internal doors need airflow for ventilation.

Which is better, brush or rubber?

Brushes suit uneven floors; rubber blades can seal more tightly on smooth surfaces.

What is a drop seal?

It lowers automatically when the door closes and lifts when opened.