How do I fix a draughty window?

Window draughts come from three different places and each has a different fix. Air moving around the opening sash needs a compression seal; air coming from around the frame needs filling; and a window that closes loosely needs adjusting rather than sealing.

What you'll need

• Self-adhesive draught strip
• Decorator's caulk and a caulking gun
• Alcohol wipes
• Allen keys for uPVC hinges and keeps (optional)
• Incense stick (optional)

Step by step

1. Find the draught precisely on a cold, windy day.A lit incense stick shows airflow clearly. Move it slowly around the whole perimeter.
2. Distinguish air coming past the opening sash from air coming around the frame.Different fixes. Sealing the wrong one achieves nothing.
3. For gaps around the opening casement, fit self-adhesive compression strip.Clean the surface with alcohol first — the adhesive fails on dusty or greasy frames.
4. Choose a strip thickness that compresses when the window closes without stopping it latching.Too thick and the window will not close; too thin and it does nothing.
5. For gaps between the frame and the wall, run a bead of decorator's caulk.Caulk stays slightly flexible, which suits a junction between two materials that move differently.
6. For a uPVC casement that no longer pulls up tight, adjust the hinges or the keeps.Most have an adjustment screw under a cover cap. Small increments — a quarter turn at a time.
7. Check the trickle vents are clear and open.They are designed ventilation. Sealing them causes condensation, which is a worse problem than the draught.
8. For sash windows, use brush-pile strip designed for sashes.It seals while still allowing the sash to slide.

Tips

• Heavy lined curtains that reach the floor make a noticeable difference to how cold a room feels, and cost nothing to close.
• Secondary glazing, even a temporary film kit, cuts both draught and heat loss substantially for very little money.
• Condensation on the room-side of double glazing is a ventilation issue; condensation between the panes means the unit's seal has failed and it needs replacing.

Common mistakes

• Sealing trickle vents — They are the designed background ventilation. Closing them is a leading cause of new condensation and mould problems.
• Fitting strip to a dirty frame — The adhesive fails within weeks. Clean with alcohol first.
• Using strip that is too thick — The window will not latch properly, which makes the seal worse rather than better.

Questions people ask