Draught-proofing your windows can cost as little as £20 for DIY foam strips or over £300 per window for professional secondary glazing, a difference of more than 15 times the upfront outlay.
If you are losing heat through gaps around your window frames, you are likely paying more for energy than you need to. Draught-proofing is one of the cheapest and quickest ways to improve home comfort and cut bills. The key is choosing the right method for your window type and the size of the gap you need to seal.
Window draught proofing costs £2-£300+ per window, with DIY foam tape at the low end and professional secondary glazing at the high end. Your choice depends on window type and gap size.
- Brush pile strips cost £5-£15 per window for sash windows.
- Self-adhesive foam tape is cheapest at £2-£10 per window.
- Secondary glazing costs £150-£300+ per window professionally fitted.
- V-strip or silicone sealant works best for casement windows.
- Draught-proofing can cut heating bills by up to £60 per year.
- Draught-proofing your windows can cost as little as £20 for DIY foam strips or over £300 per window for professional secondary glazing, a difference of more than 15 times the upfront outlay.
- Brush pile strips are the best fit for sliding sash windows
- Self-adhesive foam tape is the cheapest option for fixed gaps
- V-strip or tension seals are the most durable solution for opening casements
- Secondary glazing can reduce heat loss by 50% but is a permanent fixture
- Quick numbers
- The simplest effective method for a typical casement window is self-adhesive V-strip
- Only FENSA-registered installers should fit secondary glazing for a guarantee
Your choice depends on whether your windows are casement (side-hung), sliding sash, or fixed panes, and whether you want a temporary fix or a long-term solution. This guide compares the main window draught proofing methods available in the UK, with typical costs, lifespans, and installation requirements for each.
Brush pile strips are the best fit for sliding sash windows
Brush pile strips are made from nylon or polypropylene fibres that fill the gap between the sliding sash and the frame without blocking the mechanism. They are designed to allow the sash to move freely while blocking air movement. These strips are self-adhesive or pin-fixed, and you can trim them to length with scissors or a knife.
They work best when the gap between the sash and frame is between 3 mm and 10 mm. If the gap is tighter than 3 mm, a different profile may be needed to avoid jamming the sash. Energy Saving Trust recommends brush pile for sash windows because it does not create friction that stops the window from sliding (Energy Saving Trust, 2026).
Typical cost for a DIY kit is £5 to £15 per window, or £25 to £50 per window if professionally fitted. Lifespan is 5 to 10 years depending on exposure to weather and wear from sliding.
Self-adhesive foam tape is the cheapest option for fixed gaps
Foam tape is made from EPDM rubber or closed-cell polyethylene, and it is the cheapest draught-proofing material available. It works well on window frames where the gap is consistent, between 1 mm and 3 mm. You simply peel off the backing and press the tape into the gap.
Cost is roughly £3 to £8 for a 10-metre roll, which is enough for two or three standard casement windows. However, foam tape has a short lifespan of 1 to 3 years. It degrades in direct sunlight and may peel off in damp conditions, so it is best suited for windows that are not exposed to heavy rain or UV (Energy Saving Trust, 2026).
If you have gaps larger than 3 mm, foam tape will not compress enough to seal effectively. It also does not tolerate repeated opening and closing well, so it is best for windows you do not open often.
V-strip or tension seals are the most durable solution for opening casements
V-strips, also called tension seals, are made from PVC, silicone, or stainless steel. They are fixed to the window frame and spring into contact with the window when it is closed, creating a tight seal. Unlike foam tape, they tolerate repeated opening and closing, lasting 5 to 10 years.
Typical cost is £10 to £20 per window for a DIY kit, or £40 to £60 per window if professionally fitted. V-strips work best for gaps of 1 mm to 5 mm, and they do not require a perfectly smooth surface on the window frame (Energy Saving Trust, 2026).
Stainless steel V-strips are the most durable option and are suitable for windows that get heavy use. Silicone V-strips are more flexible and easier to install on curved frames.
Secondary glazing can reduce heat loss by 50% but is a permanent fixture
Secondary glazing involves fitting a separate pane of glass or acrylic inside the existing window frame, creating an insulating air gap of 50 mm to 150 mm. This is a permanent fixture, not a temporary seal. It is most effective on single-glazed windows, where it can reduce heat loss significantly.
The U-value of a single-glazed window is roughly 5.0 W/m²K. With secondary glazing, the U-value improves to between 2.0 and 2.5 W/m²K, meaning it cuts heat loss by about 50% compared to single glazing alone (DESNZ, 2026).
Cost ranges from £150 to £350 per window including installation, according to industry averages from the Glass and Glazing Federation. Secondary glazing is not a DIY project for most people because it requires accurate cutting and fitting, and it may need planning permission if you live in a listed building or conservation area.
Quick numbers
| Method | Typical cost per window (DIY) | Typical cost per window (fitted) | Expected lifespan | Best for gap size |
|---|---|---|---|---|
| Foam tape | £2–£8 | £15–£30 | 1–3 years | 1–3 mm |
| Brush pile strip | £5–£15 | £25–£50 | 5–10 years | 3–10 mm |
| V-strip / tension seal | £10–£20 | £40–£60 | 5–10 years | 1–5 mm |
| Secondary glazing | £50–£150 | £150–£350 | 20+ years | N/A – full pane |
The simplest effective method for a typical casement window is self-adhesive V-strip
For a standard side-hung casement window with a 2 mm to 4 mm gap, V-strip provides the best balance of durability, cost, and ease of installation. It does not require a perfectly smooth surface (unlike foam tape, which can peel off uneven frames), and you can cut it with household scissors.
It is the only draught-proofing method that remains effective after more than 1,000 opening cycles, according to Energy Saving Trust product testing (Energy Saving Trust, 2026). For most homes, this means you can fit V-strip once and not need to replace it for several years.
If you have sash windows, brush pile is the better choice because it does not jam the sliding mechanism. If you have single glazing and want a permanent thermal upgrade, secondary glazing is the most effective option despite the higher cost.
how to measure window gaps for draught-proofing
Only FENSA-registered installers should fit secondary glazing for a guarantee
FENSA (Fenestration Self-Assessment Scheme) registration is the standard for window and glazing work in England and Wales. For secondary glazing, you should check that the installer is FENSA-certified or a member of the Glass and Glazing Federation (GGF). This gives you access to a warranty and a complaints process if the work is faulty (GOV.UK, 2026).
DIY draught-proofing materials such as foam tape, brush pile, and V-strip do not require certification. However, if you decide to have any draught-proofing product professionally fitted, you should use a TrustMark-registered tradesperson. TrustMark is a government-endorsed scheme that covers work in and around your home (TrustMark, 2026).
If you are fitting secondary glazing yourself, note that the materials alone cost £50 to £150 per window. Professional installation adds £100 to £200 per window, but you get a guarantee and correct fitting that prevents condensation between the panes.
secondary glazing vs double glazing cost comparison
Frequently Asked Questions
Brush pile strips are the best method for sash windows, costing £5-£15 per window for a DIY kit. Energy Saving Trust recommends them because they allow the sash to slide freely while blocking air gaps.
Costs range from £2-£10 per window for self-adhesive foam tape to £150-£300+ per window for professional secondary glazing. DIY methods are the cheapest, according to Ofgem.
Yes, draught-proofing windows can save up to £60 per year on heating bills. Energy Saving Trust states it is one of the most cost-effective home improvements.
Self-adhesive foam tape is the cheapest method at £2-£10 per window. It works best on fixed gaps between 1-3 mm, as noted by Energy Saving Trust.
Yes, DIY draught-proofing kits are widely available. Brush pile strips, foam tape, and silicone sealant can all be installed by homeowners with basic tools, as advised by GOV.UK.
