Door Draught Proofing: How to Seal Gaps Around External Doors

Draughty external doors are one of the simplest and cheapest energy efficiency problems to fix, yet they are one of the most commonly neglected. Effective door draught proofing UK homeowners can do themselves costs as little as GBP 10 to GBP 50 per door and can save GBP 30 to GBP 60 per year on heating bills by stopping cold air pouring through gaps around the door frame, under the door, and through letterboxes and keyholes.

How to Draught-Proof an External Door

1. Check for draughts — hold a lit candle or incense stick around the door frame edges to detect air movement
2. Fit self-adhesive foam or rubber strips — press them into the door frame rebate along the top and both sides where the door closes
3. Install a brush or rubber door sweep — screw or slide it onto the bottom edge of the door to seal the gap between the door and threshold
4. Add a letterbox cover or brush plate — fit an internal flap or brush seal to block air flowing through the letterbox opening
5. Seal the keyhole — fit a keyhole cover plate that drops closed when the key is removed
6. Replace worn weatherstripping — if existing seals are cracked, compressed or peeling, remove them and fit fresh strips

Draught-proofing external doors is one of the cheapest energy efficiency improvements you can make, costing £20 to £50 in materials for a DIY job. The Energy Saving Trust estimates that sealing gaps around doors and windows saves £60 to £85 per year on heating bills in a typical UK home.

Where External Doors Lose Heat

An external door can leak air in several places, and addressing all of them is important for the draught-proofing to be effective.

• Between the door and frame (sides and top): As timber doors age, they shrink, warp, or settle, opening gaps between the door edge and the frame. Even small gaps allow significant air movement because wind pressure forces cold air through them.
• Under the door (threshold): The gap beneath the door is often the largest single source of draughts. Wind-driven rain also enters through this gap if there is no effective threshold seal.
• Letterbox: An unprotected letterbox is essentially a slot cut in the door, allowing cold air to stream into the hallway continuously.
• Keyhole: Less significant than other gaps but still a source of draughts, particularly on exposed doors.
• Cat flap: A poorly sealed or worn cat flap can leak substantial amounts of air.
• Glazing seals (in glazed doors): The seal between glass panels and the door frame can deteriorate over time.

Types of Door Draught Proofing Seals

Different parts of the door require different seal types. Using the right seal for each location ensures long-lasting, effective draught-proofing.

Compression seals (for sides and top of door)

Compression seals, also called foam or rubber strips, are the most common draught-proofing method for the sides and top of a door. They stick to the door frame (or the door itself) and compress when the door closes, creating an airtight seal.

• Self-adhesive foam strip: The cheapest option at GBP 2 to GBP 5 per door. Foam strips deteriorate within 1 to 3 years and need replacing regularly. They work best as a temporary fix.
• Self-adhesive rubber (EPDM) strip: More durable than foam, lasting 5 to 10 years. Better compression recovery means a more consistent seal. Cost: GBP 5 to GBP 12 per door.
• P-profile or E-profile rubber strip: These hollow-section strips provide excellent compression and are suitable for larger gaps. The profile shape means they seal well even when the gap varies along the door edge.

Brush strips (for sides, top, and sliding doors)

Brush strips consist of nylon bristles set in a metal or plastic carrier. They allow the door to open and close easily while blocking draughts. Brush strips are particularly effective for:

• Doors that have warped and have uneven gaps
• Sliding patio doors where compression seals would impede the sliding action
• Doors that swell in damp weather and stick if compression seals are too thick

Brush strips cost around GBP 5 to GBP 15 per door and last 5 to 10 years. They can be surface-mounted with screws or recessed into a groove routed into the door frame for a neater finish.

Threshold draught excluders (for under the door)

The gap under a door requires a different approach because the seal must allow the door to open and close over the floor surface. Several options exist:

• Brush strip (bottom of door): A strip of bristles fixed to the bottom edge of the door. Simple and effective for most gaps up to 15mm. Cost: GBP 5 to GBP 12.
• Automatic drop seal: A concealed mechanism that drops a rubber seal down when the door closes and lifts it when the door opens. This provides an excellent seal without dragging on the floor. Cost: GBP 20 to GBP 50.
• Threshold plate with rubber seal: A metal or rubber strip fixed to the floor at the threshold, which the door closes onto. Effective for both draughts and rain penetration. Cost: GBP 10 to GBP 30.
• Rise and fall hinge: Specialist hinges that lift the door slightly as it opens (clearing the floor) and drop it as it closes (onto a threshold seal). Expensive but effective for high-traffic doors. Cost: GBP 30 to GBP 60 per pair.

Door Draught Proofing UK: By Door Material

The door material affects which draught-proofing products work best.

Timber doors

Timber doors are the most problematic for draughts because wood shrinks and swells with seasonal moisture changes. A door that fits perfectly in summer may have 3 to 5mm gaps in winter when the wood dries and contracts.

For timber doors, use compression seals (EPDM rubber) on the frame sides and top, and a brush strip or automatic drop seal at the bottom. If the door is badly warped, brush strips may work better than compression seals because they accommodate uneven gaps.

uPVC doors

uPVC doors come with factory-fitted rubber gaskets in the frame. Over time (typically 10 to 15 years), these gaskets harden, crack, and lose their seal. Replacement gaskets specific to the door manufacturer can be pushed into the existing gasket channel. If the original channel is damaged, surface-mounted EPDM strips work as an alternative.

Another common issue with uPVC doors is the multipoint locking mechanism going out of adjustment. If the door does not pull tightly against the seals when locked, adjusting the lock keeps can restore a good seal. This is often more effective than adding new seals to a poorly adjusted door.

Composite doors

Composite doors are dimensionally stable and rarely warp, so factory-fitted seals tend to last well. If draught-proofing is needed, the approach is similar to uPVC: replace the gaskets in the existing channels or add surface-mounted strips. The bottom seal and threshold are the most likely areas to need attention.

Sliding patio doors

Patio doors use brush strips in the sliding track and compression seals on the fixed frame. Over time, the brushes wear flat and the seals compress permanently. Replacement brush strips for the track and new gaskets for the frame restore the seal. For older aluminium patio doors with poor inherent thermal performance, consider upgrading to modern double-glazed sliding doors that include integrated draught seals and thermal breaks.

Letterbox and Keyhole Solutions

A standard letterbox opening measures approximately 250mm x 40mm, creating a 100 square centimetre opening in your front door. Without a draught-proofing solution, this is equivalent to leaving a small window permanently open.

• Letterbox brush plate (internal): A plate with a row of nylon bristles fitted to the inside of the door behind the letterbox flap. The bristles seal the opening while still allowing post to be pushed through. Cost: GBP 5 to GBP 15. This is the most effective and popular solution.
• Letterbox cowl (external): A hooded cover fitted to the outside of the door that shields the letterbox opening from wind-driven rain and draughts. Best used in combination with an internal brush plate.
• Sprung letterbox flap: Ensuring the external flap has a working spring and closes firmly against a rubber or felt seal. Replace worn or broken flap springs promptly.
• External letterbox (porch or wall-mounted): Eliminating the door letterbox entirely by fitting a separate wall-mounted letterbox. This removes the opening from the door completely but requires redirecting post delivery.

For keyholes, a simple keyhole cover plate that rotates to cover the hole when the key is not inserted costs GBP 3 to GBP 8 and eliminates the draught.

Expected Energy Savings from Door Draught Proofing

The Energy Saving Trust estimates that draught-proofing all external doors in a typical home saves approximately GBP 60 per year on heating bills. Given that materials for a full door draught-proofing kit cost GBP 10 to GBP 50 per door, the payback period is typically under one year.

Beyond energy savings, draught-proofing improves comfort enormously. Cold draughts across the floor near doors are one of the most commonly reported comfort complaints in UK homes, and eliminating them makes the hallway and adjacent rooms feel significantly warmer without increasing the thermostat setting.

Door draught-proofing is an ideal complement to broader insulation improvements. For a comprehensive assessment of where your home is losing heat, request a free energy assessment.

Frequently Asked Questions About Door Draught Proofing

Should I draught-proof my front door if I have trickle vents?

Yes. Trickle vents in windows provide controlled background ventilation; gaps around doors allow uncontrolled, wind-driven draughts. The two serve different purposes. Draught-proofing your doors and relying on trickle vents for ventilation is the correct approach. Never seal trickle vents to compensate for other draughts.

How do I measure the gap around my door?

Close the door and look for daylight around the edges. Use a coin or feeler gauge to measure the gap width. Gaps up to 3mm are normal and can be sealed with standard compression strips. Gaps of 3 to 6mm need thicker P-profile or brush strips. Gaps over 6mm suggest the door needs adjustment (rehinging or planing) before draught-proofing.

Can I draught-proof a door that sticks in summer?

If a timber door swells in summer, fitting thick compression seals may make the sticking worse. Use brush strips instead, which allow more tolerance for movement. Alternatively, have the door planed to fit properly in summer and use compression seals to take up the gap that appears in winter.

Is it worth paying a professional to draught-proof my doors?

Door draught-proofing is one of the most straightforward DIY tasks. Self-adhesive strips require no tools beyond scissors. Brush strips need a screwdriver or drill. Automatic drop seals require cutting a groove, which needs a router or careful work with a chisel. For most homeowners, DIY is practical and saves the cost of a professional visit, which typically adds GBP 50 to GBP 100 per door.