1. Seal the bottom gap with a brush strip
Brush strips block the largest draught source and cost £10–£25 from DIY stores. They are fitted to the bottom of the door, using a series of bristles that press against the floor to seal the gap. The Energy Saving Trust says fitting a brush strip can save around £30–£60 per year on heating bills (Energy Saving Trust, 2026).
- Measure the gap between the door and the floor before buying; strips come in different bristle lengths.
- Brush strips are best for smooth, level floors like wood or tile.
- Check the fixings match your door material (wood, uPVC, or metal).
How to measure gaps for draught-proofing products
2. Use a hinged flap seal for uneven floors
Hinged flaps automatically drop to seal against uneven or carpeted floors, costing £15–£30. They mount on the door face and use a weighted flap that pivots to contact the floor, even on slopes or thick pile carpets. TrustMark recommends these where brush strips cannot maintain consistent contact (TrustMark, 2026).
- Ideal for external doors with high thresholds or uneven stone floors.
- Flap seals are more durable than brush strips in high-traffic areas.
- Ensure the flap is long enough to cover the full width of the door.
3. Fit self-adhesive foam tape to the frame
Foam tape fills gaps between the door and frame, costing £5–£10 per door. It is applied to the door stop where the door meets the frame, compressing when the door closes to create a seal. The Energy Saving Trust advises replacing tape every one to two years as it compresses and loses effectiveness (Energy Saving Trust, 2026).
- Choose the correct thickness: the tape should compress by about 50% when the door is closed.
- Clean the frame surface thoroughly before application to ensure adhesion.
- Foam tape works best on even gaps up to 5mm wide.
4. Install a draught-proof letterbox cover
A letterbox can let in as much cold air as a 10mm gap around the door; a brush or flap cover costs £8–£15. These covers fit over the internal or external side of the letterbox, using bristles or a hinged flap to block airflow when the flap is not in use. FENSA guidance states letterbox covers are a quick, low-cost retrofit (FENSA, 2026).
- Check the cover size matches your letterbox dimensions.
- Brush covers allow mail to be pushed through while still blocking draughts.
- External covers may need weatherproofing to avoid rain ingress.
5. Add a keyhole cover on a chain
A small metal cover with a chain costs £2–£5 and stops a persistent but narrow draught. The cover slides over the keyhole when the key is not in use, and the chain keeps it attached to the door so it is not lost. The Energy Saving Trust lists keyhole covers as a “very cheap” fix with immediate effect (Energy Saving Trust, 2026).
- Brass or nickel-plated covers are available to match existing door furniture.
- Fitting takes under a minute with a single screw.
- Keyhole covers are especially useful for older wooden doors with large keyholes.
6. Check and seal the door threshold
A worn or missing threshold strip can cause a large bottom gap; replacement strips cost £15–£40. The threshold sits at the bottom of the door frame and often has a built-in seal that degrades over time. TrustMark says thresholds should be checked annually for compression or damage (TrustMark, 2026).
- Replace the entire threshold strip if the seal is cracked or flattened.
- Adjustable thresholds can be raised or lowered to close gaps without replacement.
- Ensure the new threshold matches the door width and floor profile.
7. Use a draught excluder sausage for temporary gaps
Fabric sausages cost £5–£15 and are ideal for doors not used often or for rented homes. They are placed at the base of the door and rely on weight or filling (often sand or foam) to block the gap. The Energy Saving Trust notes they are a no-tools solution but less effective than a permanent seal (Energy Saving Trust, 2026).
- Choose a sausage with a non-slip base to prevent it shifting when the door opens.
- Fill with rice, sand, or foam beads for weight and flexibility.
- Not suitable for doors that are opened frequently, as the seal is displaced each time.
8. Seal gaps around a cat flap
Cat flaps are common draught points; replacement insulated flaps or brush surrounds cost £10–£25. The flap itself can be replaced with a magnetic or insulated version that seals more tightly after the cat passes through. GOV.UK advises checking cat flaps as part of a whole-home draught-proofing plan (GOV.UK, 2026).
- Magnetic cat flaps use magnets to pull the flap closed after use.
- Brush surrounds fit around the flap frame to block gaps where the frame meets the door.
- Insulated flaps have foam cores to reduce heat loss through the flap itself.
9. Apply silicone sealant to fixed door panels
Gaps around fixed side panels or transoms can be sealed with silicone, costing £5–£10. These are non-moving joints where foam tape would be crushed or dislodged, so a bead of silicone creates a permanent flexible seal. TrustMark recommends silicone for non-moving joints to avoid interfering with door operation (TrustMark, 2026).
- Use a silicone sealant that is paintable if you want to match the frame colour.
- Apply a smooth bead with a caulking gun and tool it with a wet finger for a neat finish.
- Allow 24 hours for curing before painting or exposing to moisture.
10. Replace worn or missing weatherstripping on patio doors
Sliding patio doors often lose their pile or rubber seals; replacement strips cost £10–£20. The weatherstripping runs along the edges of the sliding panel and the fixed frame, and when worn, it leaves a gap that lets in cold air. The Energy Saving Trust states replacing weatherstripping on sliding doors can cut heat loss by up to 10% (Energy Saving Trust, 2026).
- Remove the old strip and clean the channel before inserting the new one.
- Choose weatherstripping with a pile height that matches the original specification.
- Check the bottom track seal as well, as this is often the first part to wear.
How to draught-proof sliding patio doors effectively
Stopping door draughts is one of the cheapest and most effective ways to reduce home heat loss, saving up to £60 a year. Start with the largest gap, usually at the bottom of the door, and work through the frame, letterbox, and keyhole for a complete seal.
Frequently Asked Questions
An Energy Saving Trust study in 2026 found brush strips save £30–£60 per year. They block the largest draught source at the bottom of the door.
Brush strips are the most effective for smooth floors, while hinged flap seals work best on uneven or carpeted surfaces. The Energy Saving Trust recommends brush strips for standard doors.
Foam tape should be replaced every one to two years, according to the Energy Saving Trust. It compresses over time and loses its sealing ability.
Yes, a letterbox can let in as much cold air as a 10mm gap around the door. A brush or flap cover costing £8–£15 effectively seals it.
Yes, measure the gap between the door and floor to choose the correct bristle length. Strips come in different sizes for different gaps.
