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DRAUGHTS & SEALS

Window Rubber Seal Shrunk

A window gasket can shrink with age, heat and poor installation, leaving gaps at corners and reducing weather sealing.

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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

Age-related contraction Rubber loses flexibility and shortens.
Stretching during fitting The gasket later pulls back to its natural length.
Heat and sunlight Temperature cycling accelerates shrinkage.
Wrong gasket profile Poor fit allows movement in the groove.
◫ Symptom variations Match the draught, gap or seal pattern. ⌄
  • Gap at gasket corner
  • Seal has pulled away from frame
  • Draught at one point
  • Water marks near corner
  • Rubber feels hard
✓ Quick checks Safe checks before replacing seals. ⌄
  1. Inspect all corners.
  2. Check whether the seal is removable.
  3. Compare profile with an intact section.
  4. Look for blocked drainage slots.
  5. Check sash alignment.
Important: Find the exact leak path first. Replacing the wrong seal can make closing harder without fixing the fault.
1 Step 1 — Confirm the gasket is the leak source Make the smallest safe correction and retest. ⌄

Rule out frame sealant and hinge faults.

2 Step 2 — Remove a sample carefully Make the smallest safe correction and retest. ⌄

Use it to match the exact profile.

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

Do not stretch it and make neat corner joints.

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

Rubber contracts over time, especially when originally stretched into place. Corners usually reveal the movement first.

⌘ Advanced checks Further diagnosis for persistent sealing faults. ⌄
  1. Measure groove dimensions.
  2. Identify bubble, flipper or wedge profile.
  3. Check compression around the sash.
  4. Assess glazing gasket separately.
  5. Inspect drainage channels.
◇ Tools and information needed Useful items for accurate checks. ⌄
  • Plastic trim tool
  • Tape measure
  • Scissors
  • Gasket lubricant where approved
  • Replacement seal
▣ Parts or improvements that may help Common sealing products linked to this problem. ⌄
  • Matching gasket
  • Corner adhesive where specified
  • Glazing gasket
  • Keeps
  • Hinges
! When to call a professional Conditions that should end basic DIY diagnosis. ⌄
  • The glazing gasket is affected.
  • The glass unit moves.
  • The frame is high-level.
  • Water ingress persists after replacement.
  • The correct profile cannot be identified.
? Frequently asked questions Common draught and seal questions. ⌄

Can I just stretch the old seal back?

It will usually shrink again and may leave thinner sections.

Do I need to replace the whole perimeter?

Usually yes for a consistent seal.

Can the wrong gasket make the window stiff?

Yes. An oversized profile can overload the locking mechanism.