Weather-sealing windows and doors typically costs between £5 and £50 per window or door and can reduce heat loss by up to 20% according to the Energy Saving Trust (Energy Saving Trust, 2026). The exact method depends on whether you have draughts around the frame, between the sash and frame, or under the door.
The most common cause of draughts is worn or missing seals. For windows, the seal sits between the opening sash and the fixed frame. For doors, the seal runs around the edge of the door leaf. You can buy self-adhesive foam strips, silicone sealant, or brush strips from any DIY store. The cost is low and the job takes under an hour per window or door. However, if the frame itself is rotten or the glass unit is failing, weather sealing alone will not fix the problem.
Identify the draught source first
Hold a lit incense stick or a thin piece of tissue paper near the edges of the window or door while it is closed. If the smoke or paper moves, you have a draught. The Energy Saving Trust advises checking all four sides of the frame and the gap between the door and the floor (Energy Saving Trust, 2026). For windows, also check the meeting rail where two sashes overlap. Mark the spots with pencil so you know exactly where to apply the seal.
Apply self-adhesive foam or silicone sealant
For gaps up to 5mm wide, use self-adhesive foam strips. Cut the strip to length, peel off the backing, and press it into the gap. For gaps up to 10mm, use silicone sealant applied with a caulking gun. The BRE recommends silicone because it remains flexible and does not shrink (BRE, 2026). For doors, use a brush strip or a rubber threshold seal. Brush strips are better for uneven gaps and last longer than foam.
Check and replace existing seals annually
Even good seals wear out. The MCSCertified scheme notes that window seals typically last 5 to 10 years depending on sunlight exposure and usage (MCSCertified, 2026). Inspect seals each autumn before heating season starts. Peel back a corner of the strip, if it crumbles or no longer springs back, replace it. Clean the frame surface with warm soapy water and let it dry fully before applying new sealant or strips. This simple check costs nothing and can save you up to £45 per year on heating bills according to the Energy Saving Trust (Energy Saving Trust, 2026).
A worked example
A typical 1930s semi-detached house in Manchester with three draughty single-glazed sash windows and a front door can have its weather sealing completed for around £85. The homeowner identifies four draught points using the incense stick method, three around the window sashes and one under the door. They buy self-adhesive foam strips for the windows at £8 each and a brush strip for the door at £15, totalling £39 in materials. Labour takes two hours. The Energy Saving Trust estimates this reduces heat loss by up to 20%, which for this property means annual savings of roughly £120 on heating bills (Energy Saving Trust, 2026).Glazing is standard-rated for VAT at 20%. The zero rate for energy-saving materials covers insulation, heat pumps and solar panels; HMRC names secondary and double glazing as excluded (VAT Notice 708/6).
| Item | Figure |
|---|---|
| Upfront cost after grants | £85 |
| Yearly savings | £120 |
| Payback period | 0.7 years |
| 25-year lifetime savings | £2,915 |
What homeowners often get wrong
The most common mistake homeowners make when weather sealing windows and doors is assuming one type of seal works for every gap size. This leads to wasted money and ineffective draught-proofing. Here are three specific errors to avoid.
- Using foam strips on gaps larger than 5mm The misconception is that thicker foam will compress and seal a wide gap. The right answer is that gaps over 5mm need a brush strip or silicone sealant instead, or the foam will tear within a month, leaving you back where you started and wasting the £8 you spent.
- Ignoring the door threshold gap Many homeowners seal the sides and top of a door but forget the bottom. The misconception is that a draught excluder is only needed for winter. The right answer is that a brush strip fitted to the bottom of the door stops both draughts and debris all year round, and missing this can lose up to 15% of your heating savings.
- Applying sealant to a damp or dirty frame The misconception is that silicone sealant will stick to any surface. The right answer is that it must be applied to a clean, dry surface at temperatures above 5°C, or it will peel off within weeks, voiding the warranty and costing you another £10 to redo the job.
Quick reference
- Self-adhesive foam strips cost £5 to £10 per window and are ideal for gaps up to 5mm wide.
- Brush strips for doors cost £10 to £20 and suit gaps between 5mm and 15mm.
- Glazing is standard-rated for VAT at 20%. The zero rate for energy-saving materials covers insulation, heat pumps and solar panels; HMRC names secondary and double glazing as excluded (VAT Notice 708/6).
- Draught-proofing the whole house typically pays for itself within one to two years through lower energy bills.
- Check for rotten frames or failing glass units before sealing, as these need repair first or the seal will fail.
Frequently Asked Questions
The cost is between £5 and £50 per window or door according to the Energy Saving Trust. Self-adhesive foam strips and silicone sealant are the cheapest options.
Hold a lit incense stick or tissue paper near the edges while the window is closed. The Energy Saving Trust recommends checking all four sides and the meeting rail.
Yes, the job takes under an hour per window or door. Use self-adhesive foam strips for gaps up to 5mm or silicone sealant for gaps up to 10mm.
