Draught Proofing Windows & Doors: Seals, Strips & Threshold Solutions

Summary

Draught proofing addresses air infiltration around windows and doors — uncontrolled air movement that wastes heat and creates cold spots and discomfort. Unlike deliberate ventilation (trickle vents, extraction fans), draughts are uncontrolled and contribute nothing to indoor air quality — they are purely a heat loss mechanism. Older UK housing in particular is significantly draughty; pre-1980s timber windows and doors that have not been maintained or draught-proofed can account for a significant fraction of the total air infiltration of a property.

There are two distinct categories: casement/hinged windows and doors (where a compression seal closes against a rebate), and sliding components like sash windows and letterboxes (which require brush pile seals that allow the sliding movement). The correct product type for each application is critical — fitting a compression seal where a brush pile seal is needed will either prevent the component from closing or will wear out rapidly.

One important caveat: draught proofing should not block controlled ventilation. Many older windows have intentional gaps or trickle vents that are part of the ventilation strategy of the property. Block these and condensation and mould may result. Similarly, sealing chimneys and letterboxes completely (as opposed to fitting brush seals) can significantly reduce air supply, particularly important in properties with open-flue gas appliances. Always assess ventilation implications before extensive draught proofing.

Key Facts

• Energy Saving Trust estimate — £45–£60/year savings from draught proofing doors and windows (2024 estimate; varies with fuel costs and property type)
• Compression seal — foam, rubber, or silicone seal that compresses when the door or window closes; best for hinged/casement applications; comes in self-adhesive, push-in-slot, and screw-fixed types
• Brush pile seal — nylon or polypropylene pile in a metal or plastic carrier; allows sliding movement; used for sash windows and letterboxes
• Threshold strip — aluminium, uPVC, or timber strip at the base of a door; incorporates a rubber or brush seal against the floor
• Door bottom seal — spring-loaded or hinged seal that drops onto the floor when the door closes; completely seals the gap; trip hazard risk if poorly specified
• Silicone sealant — used for filling gaps in window frames and between window frames and masonry; paintable silicone or acrylic sealant rather than standard glazing silicone in visible locations
• Letterbox seal — brush pile curtain behind the letterbox flap; prevents cold air from entering through the letterbox
• Keyhole covers — spring-loaded escutcheons; very small benefit but complete the draught-proofing picture
• Part F (ventilation) — when draught proofing, trickle vents must not be sealed; existing background ventilation (perforated bricks, air bricks) must be retained
• Open flue appliances — if the property has an open-flue boiler, gas fire, or solid fuel appliance, significant draught proofing that reduces air supply can cause dangerous flue draught reversal; seek advice from a Gas Safe engineer before extensive sealing
• Sash window seals — specialist sash window draught strips (such as Polypropylene pile or spring metal strips) can be retrofitted to the meeting rail, staff bead, and parting bead positions; professionally installed sash window draught proofing is available as a service
• Condensation risk — draught proofing a cold single-glazed window can increase condensation on the glass; the improved insulation reduces the glass temperature differential causing surface condensation, but if airtightness is increased without adequate ventilation, condensation may increase elsewhere

Quick Reference Table

Detailed Guidance

Assessing Where Draughts Are Coming From

Before purchasing products, identify the actual draught sources. Methods:

Candle/incense stick test — on a windy day, hold a lit candle or incense stick near suspected draught locations; the flame or smoke will deflect toward or away from a draught. Safe, simple, effective.

Tissue paper test — damp a sheet of tissue paper slightly and hold it near the suspect area; any air movement will visibly disturb the tissue.

Thermal camera — infrared thermography clearly shows cold air infiltration as blue areas on walls and around window/door frames. Most effective in cold weather with a warm interior.

Hand check — simply run your hand around window and door frames, skirting boards, and letterboxes on a cold or windy day; cold air movement is easily felt.

Common draught locations in order of significance:

1. Floorboards (particularly at room perimeters and around pipes)
2. Doors and windows (frame seals)
3. Letterboxes
4. Fireplace/chimney openings
5. Loft hatch
6. Gaps around pipes and cables through external walls
7. Gaps between skirting and floor

Fitting Compression Seals to Doors

Self-adhesive foam seal (cheapest option):

1. Clean the rebate with a dry cloth; ensure no dirt or old adhesive remains
2. Cut the foam seal to length; peel off the adhesive backing
3. Press firmly into the rebate (the face against which the door closes)
4. Allow the adhesive to cure for 1 hour before using the door
5. Test the door closes without forcing — trim if needed

Self-adhesive foam is inexpensive but typically lasts only 3–5 years before the foam compresses permanently. It suits interior rooms or temporary use. For external doors, use an EPDM rubber compression seal.

EPDM rubber push-in seal (better quality, longer life):

1. Many timber door frames have a pre-cut slot in the rebate for a 'P-profile' or 'D-profile' seal; push the seal into this slot
2. If no slot: use a slot cutter to cut a 3mm wide slot; or use a screw-fixed carrier strip
3. EPDM seals last 10–15 years and compress well without permanently deforming

Silicone or wiper seal for aluminium and uPVC frames:

• Modern uPVC frames have integrated seal channels; replacement seals (wedge-type or bubble-type) push into the channel; match the profile exactly
• Replacement uPVC door/window seals are available from trade suppliers (Reddiplex, Rubber-Cal)

Sash Window Draught Proofing

Sash windows are the most draughty window type due to the sliding mechanism, but they are an important architectural feature in period properties and should not be replaced unnecessarily. Effective draught proofing of sash windows involves sealing four locations:

1. Meeting rail (where the two sashes meet in the middle) — brush pile seal in a carrier strip fixed to the upper sash, bearing against the lower sash meeting rail
2. Staff bead (outer channels) — spring metal strip or brush pile in the outer face of the outer sash run
3. Parting bead (between inner and outer sash runs) — brush pile in the parting bead groove
4. Top and bottom — compression seal at the top of the upper sash (against the top frame) and bottom of the lower sash (against the sill)

DIY sash window draught proofing kits are available (Ronseal, Exitex) but professional installation by a specialist window restoration firm gives better results, particularly for listed or high-value period windows.

Threshold Seals for Doors

The gap under an external door is one of the largest single draught paths in a typical UK house. Standard thresholds:

Threshold bar with rubber insert — a standard aluminium bar (typically 45–65mm wide) with an EPDM rubber seal compressed by the door. Fixed to the floor threshold. Suitable where the door closes on a hard floor. Requires accurate height setting.

Automatic door bottom seal — a seal housed in a channel on the bottom of the door; a spring mechanism drops the seal to the floor when the door closes, and lifts it when the door opens to avoid friction. More effective than a threshold bar but requires fitting to the door itself. Examples: Pemko 315CN, Reddiplex auto-seal.

Brush strip — a strip of flexible brush pile attached to the bottom of the door; simpler than an automatic seal; best for slightly uneven floors where a rubber seal would snag.

15mm maximum threshold height — Approved Document M states that thresholds should be no more than 15mm high to meet accessibility requirements; even 15mm is a trip risk for mobility-impaired users. Many modern threshold solutions are flush or near-flush.

Sealing Gaps at the Frame-to-Masonry Junction

The gap between a timber window or door frame and the surrounding masonry is a significant air leakage path and frequently overlooked. This gap is often filled only with expanding foam (which may have degraded over time) or old mortar that has cracked.

1. Remove any loose or cracked filler material
2. Clean and prime the surfaces
3. Apply backer rod (polyethylene foam cord) if the gap is over 6mm deep, to control the depth of sealant application
4. Apply a compatible paintable acrylic/silicone hybrid sealant; tool with a wet finger to create a concave profile
5. Allow to cure; paint to match the surrounding surface

Use a neutral-cure silicone (or paintable acrylic sealant for painted surfaces) rather than standard acidic (acetoxy) silicone which can stain and corrode metal window frames.

Frequently Asked Questions

Will draught proofing cause condensation problems?

Only if the property is already poorly ventilated. If trickle vents are retained, extract fans are working correctly, and background ventilation is maintained, draught proofing should not cause condensation problems. If anything, reducing cold infiltration air slightly reduces the amount of cold air that enters and then warms up, absorbing moisture from interior surfaces. The key is not to seal intentional ventilation openings.

Can I draught-proof a letterbox completely?

A brush pile curtain reduces air infiltration through the letterbox dramatically while still allowing letters to pass through. A hard seal that completely closes the letterbox is not appropriate — postal deliveries are made through the letterbox and completely sealing it prevents this. Fit a brush pile curtain; for additional draught reduction, consider a letterbox plate cover on the external face.

My old timber sash windows are draughty — should I just replace them?

Not necessarily. Well-maintained and draught-proofed timber sash windows can perform comparably to double-glazed uPVC windows in terms of heat loss, particularly if secondary glazing is also fitted. Replacement of period sash windows in conservation areas or listed buildings may require planning/listed building consent. The embodied carbon cost of new uPVC windows also exceeds the energy savings for many years. Sash window restoration and draught proofing is often the more sustainable and cost-effective option.

Regulations & Standards

• Building Regulations Approved Document F (2021) — Ventilation: draught proofing must not block controlled ventilation openings including trickle vents and background ventilators

• Building Regulations Approved Document M — Accessibility: maximum 15mm threshold height for accessible entrance doors

• Energy Saving Trust — Draught proofing guidance and estimated savings

• Part P — Draught proofing is not notifiable work; no electrical work involved

• Energy Saving Trust — Draught Proofing — Savings estimates and DIY guidance

• Historic England — Draught Proofing Period Windows — Guidance on draught proofing listed and historic buildings

• Reddiplex UK — Seals and Threshold Products — Technical data for rubber and brush pile seals

• Sash Window Expert — Draught Proofing Service — Professional sash window draught proofing

• window types — Window types, glazing requirements, FENSA certification

• airtightness — Whole-building airtightness and pressure testing

• ventilation strategy — Ensuring adequate ventilation after draught proofing

• condensation — Condensation risk management