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GLASS & SEALED UNITS

Draught From Double Glazing

A draught around double glazing usually comes from the opening sash, frame perimeter or trickle vent rather than through the glass itself.

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Treat cracked or loose glass as hazardous

Do not press, lever or dismantle glazing unless the pane is safely supported. Large, high-level and safety-critical glass needs professional handling.

MOST LIKELY CAUSES

Start with the glass, seals and frame support

Worn sash gasket The opening seal no longer compresses.
Dropped hinges One corner does not close tightly.
Misaligned locking points Cams fail to pull the sash against the frame.
Poor frame installation Air leaks around the frame-to-wall joint.
◫ Symptom variations Match the misting, cracking, rattling or water pattern. ⌄
  • Cold air near one corner
  • Whistling in wind
  • Draught stops when sash is pulled
  • Air felt around trim
  • Glass itself feels cold but no airflow is found
✓ Quick checks Safe checks before disturbing the glazing. ⌄
  1. Use a tissue around the sash perimeter.
  2. Check trickle vents.
  3. Inspect gasket condition.
  4. Look for hinge drop.
  5. Test around frame trim separately.
Important: Avoid pressure near cracked glass and never block window drainage slots.
1 Step 1 — Find the exact route Make the smallest safe correction and retest. ⌄

Separate sash, vent and frame leaks.

2 Step 2 — Restore alignment and compression Make the smallest safe correction and retest. ⌄

Adjust hinges or keeps carefully.

3 Step 3 — Repair seals and perimeter joints Make the smallest safe correction and retest. ⌄

Replace gaskets or reseal frame gaps appropriately.

⌁ Why the problem happens How sealed units, glazing support and drainage affect performance. ⌄

Glass does not normally leak air. Draughts pass through gaps around the sash, vents or frame installation.

⌘ Advanced checks Further diagnosis for persistent glazing faults. ⌄
  1. Check cam compression.
  2. Inspect external sealant.
  3. Assess cavity closers and internal trim gaps.
  4. Check frame bowing.
  5. Use controlled smoke testing.
◇ Tools and information needed Useful items for accurate checks. ⌄
  • Tissue
  • Torch
  • Allen keys
  • Sealant tools
  • Tape measure
▣ Parts that may need replacing Common glazing components linked to this fault. ⌄
  • Window gasket
  • Keeps
  • Friction hinges
  • Exterior sealant
  • Trickle vent components
! When to call a professional Conditions that should end basic DIY diagnosis. ⌄
  • The frame is loose.
  • Water ingress is present.
  • The window is high-level.
  • The sash cannot lock securely.
  • The installation gap requires opening-up work.
? Frequently asked questions Common glass and sealed-unit questions. ⌄

Can air pass through double-glazed glass?

No. The draught comes from gaps around it.

Why does the glass feel cold?

Cold glass can create downward air movement that feels like a draught.

Will new gaskets always fix it?

Only if the gasket is the actual leak source.