The most effective way to seal windows and doors is to apply silicone or acrylic sealant around frames and fit self-adhesive foam tape to opening edges, which can cut draughts by up to 25% and save around £70 a year on energy bills, according to the Energy Saving Trust (Energy Saving Trust, 2026).
Sealing works best for homes with single glazing or older double glazing that has gaps around the frame or between the sash and frame. It is less effective if the window or door is severely warped or rotten, in which case replacement may be needed. The method you choose depends on the gap size: foam tape for gaps up to 3mm, silicone sealant for gaps up to 5mm, and metal or plastic draught strips for larger gaps. All materials are widely available at UK DIY stores and cost between £5 and £20 per window or door.
Seal gaps around the frame with silicone
For gaps between the window or door frame and the wall, use a silicone or acrylic sealant applied with a caulking gun. Clean the area first, then cut the nozzle at a 45-degree angle and run a continuous bead along the gap. Smooth it with a wet finger or tool. This is suitable for fixed gaps up to 5mm and costs around £6 per tube (Energy Saving Trust, 2026). Allow 24 hours to cure before painting. Do not use this on moving parts like the sash or door edge.
Fit self-adhesive foam tape to opening edges
For gaps between the opening window or door and its frame, self-adhesive foam tape is the simplest solution. Measure the perimeter, cut the tape to length, and press it onto the clean, dry surface where the sash meets the frame. Use closed-cell foam for better durability. This works best on gaps up to 3mm and costs roughly £5–£10 per roll (GOV.UK, 2026). It needs replacing every one to two years as the foam degrades.
Use draught strips for larger or uneven gaps
For gaps wider than 3mm or uneven gaps, use rigid draught strips made of metal or plastic with a brush or rubber seal. These are screwed or stuck onto the frame. Measure the gap width and buy the correct strip. A typical strip costs £10–£20 per door or window (Energy Saving Trust, 2026). They last several years and work well on outward-opening doors and sash windows. Check the strip does not prevent the door or window from closing fully.
A worked example
A typical 1930s semi-detached house in Manchester with three draughty single-glazed sash windows and one external door can be fully sealed for roughly £80 in materials, saving around £210 a year on heating bills. This scenario assumes you seal gaps between the frame and wall with silicone sealant (£6 per tube, three tubes needed) and fit self-adhesive foam tape (£5 per window, three windows) plus a draught excluder strip for the door (£15). The Energy Saving Trust confirms that sealing draughts can reduce heat loss by up to 25% in older homes, making this one of the most cost-effective upgrades available. 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). Payback is achieved within five months, and the seals last three to five years before needing replacement.
| Item | Figure |
|---|---|
| Upfront cost after grants | £80 |
| Yearly savings | £210 |
| Payback period | 5 months |
| 25-year lifetime savings | £5,250 |
What homeowners often get wrong
The most common mistake when sealing windows and doors is using silicone sealant on moving parts like the sash or door edge, which prevents the window or door from closing properly. Here are three frequent errors to avoid.
- Applying sealant to opening edges instead of fixed gaps Silicone is designed for gaps between the frame and the wall, not for the gap between the sash and the frame. Using it on moving parts can crack the seal within weeks and may void your window warranty, costing £50 to £200 for professional removal.
- Choosing the wrong tape for the gap size Many homeowners buy standard foam tape for a 5mm gap, but foam tape only works for gaps up to 3mm. For larger gaps, you need metal or plastic draught strips, or the tape will peel off within a month, wasting the £10 you spent.
- Ignoring the letterbox and keyhole People seal windows and doors but forget the letterbox and keyhole, which can let in as much cold air as a small open window. Fitting a letterbox brush costs £8 and a keyhole cover costs £3, yet missing these can reduce your overall savings by up to 20%.
Quick reference
- Sealing gaps around windows and doors can cut draughts by up to 25% and save around £70 a year per home, according to the Energy Saving Trust.
- Foam tape works for gaps up to 3mm, silicone sealant for gaps up to 5mm, and metal or plastic draught strips for larger gaps.
- You do not need any government grants for this upgrade because materials cost between £5 and £20 per window or door. That makes it affordable for most households.
- The payback period for sealing three windows and one door is typically five months, with seals lasting three to five years before needing replacement.
- Using silicone sealant on moving parts like a sash or door edge is a common mistake that can prevent the window or door from closing and may void your warranty.
Frequently Asked Questions
Apply silicone or acrylic sealant around frames and fit self-adhesive foam tape to opening edges. The Energy Saving Trust says this cuts draughts by up to 25% and saves around £70 a year.
Materials cost between £5 and £20 per window or door, according to the Energy Saving Trust. A tube of silicone sealant costs around £6.
Yes, sealing windows and doors is a simple DIY task. Use foam tape for gaps up to 3mm and silicone sealant for gaps up to 5mm, both available at UK DIY stores.
