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DRAUGHTS & SEALS

Water Coming Under Door

Water under a door usually comes from a failed threshold seal, blocked drainage, poor external falls or water levels higher than the threshold.

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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

Failed threshold seal Water passes beneath or around the bottom seal.
Blocked drainage Channels and weep holes cannot discharge rainwater.
External level too high Paving or decking directs water toward the doorway.
Poor threshold or frame sealant Water bypasses joints around the frame.
◫ Symptom variations Match the draught, gap or seal pattern. ⌄
  • Leak only during heavy rain
  • Water appears at corners
  • Threshold channel holds water
  • External paving slopes inward
  • Draught accompanies the leak
✓ Quick checks Safe checks before replacing seals. ⌄
  1. Dry the area and identify the first wet point.
  2. Clear visible drainage slots.
  3. Inspect bottom and corner seals.
  4. Check external ground fall away from the door.
  5. Look for cracked perimeter sealant.
Important: Find the exact leak path first. Replacing the wrong seal can make closing harder without fixing the fault.
1 Step 1 — Restore drainage Make the smallest safe correction and retest. ⌄

Clear channels and ensure water can escape outside.

2 Step 2 — Repair seals and joints Make the smallest safe correction and retest. ⌄

Replace failed threshold seals and reseal suitable external joints.

3 Step 3 — Correct external water direction Make the smallest safe correction and retest. ⌄

Improve falls, drainage or threshold protection where levels are wrong.

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

Door thresholds manage water through seals and drainage paths. When water is trapped or directed toward the opening, it finds the lowest joint.

⌘ Advanced checks Further diagnosis for persistent sealing faults. ⌄
  1. Hose-test small areas in stages.
  2. Inspect sill end caps.
  3. Check cavity trays or damp-proof details.
  4. Measure external level against threshold.
  5. Assess canopy and exposure.
◇ Tools and information needed Useful items for accurate checks. ⌄
  • Torch
  • Cleaning brush
  • Sealant tools
  • Spirit level
  • Absorbent paper
▣ Parts or improvements that may help Common sealing products linked to this problem. ⌄
  • Threshold gasket
  • Frame sealant
  • Drainage channel
  • Door bottom seal
  • Sill end caps
! When to call a professional Conditions that should end basic DIY diagnosis. ⌄
  • Water enters in normal rainfall.
  • External ground is above the damp-proof level.
  • The frame or subfloor is rotten.
  • The leak affects electrics or flooring.
  • Major threshold or drainage work is required.
? Frequently asked questions Common draught and seal questions. ⌄

Why does it leak only in driving rain?

Wind pressure can push water past weak seals and overwhelmed drainage.

Can I seal the drainage holes?

No. They are designed to let water escape.

Could paving be the cause?

Yes. High or inward-sloping paving is a common cause.