Draughts Around Windows & Doors — Causes & Fixes

The symptoms

Cold air felt around the edges of windows and doors, not just through them
Draughts continuing after new double or triple glazing was installed
Condensation or mould forming on cold reveals around openings
Whistling or air movement at frame perimeters in windy weather

The building physics: the frame-to-wall junction

When a window or door is installed, a gap is left between the frame and the structural opening to allow for fitting and movement. That gap must be closed with a continuous air barrier and insulation. Too often it is only filled with expanding foam or simply hidden behind internal trim. Expanding foam insulates but is not a reliable air seal — and trim hides the gap without sealing it. The result is a continuous leakage path running around the entire perimeter of every opening.

Original timber sash windows add their own paths: the box behind the frame and old shutter cavities can act as air channels. Worn brush seals and perished weatherstrips on opening lights and doors complete the picture. And the reveal — the wall surface returning to the frame — is often a cold thermal bridge, so it both leaks and grows mould.

The likely causes

Unsealed frame-to-wall perimeter behind the trim or architrave
Worn, missing or compressed weatherseals on opening lights and doors
Original sash-window boxes and shutter cavities acting as air paths
Cold, uninsulated reveals and lintels around the opening

Why new windows can still feel draughty

A high-performance window is only as good as its installation. If the installer did not air-seal and insulate the frame-to-wall junction, the new unit sits in a leaky hole and the draughts continue. This is one of the most common post-installation complaints — and the reason we always check the perimeter, not just the glazing, with smoke tracing under a blower door test.

Common mistakes homeowners make

Replacing the glazing but never sealing the frame-to-wall junction
Relying on internal trim to 'cover' a draught rather than sealing the air path
Ignoring cold reveals, which then grow mould

How RetrofitIQ investigates window and door leakage

Blower door depressurisation with smoke tracing around every frame perimeter
Thermal imaging to reveal cold air tracking in around frames and reveals
Surface-temperature checks on reveals to assess condensation risk
A targeted sealing and reveal-detailing specification
Verification that the perimeter leakage has actually been reduced

Common questions from clients.

I have new windows but still feel draughts — why?

Almost always the frame-to-wall perimeter was not air-sealed during installation, or the reveals are cold. Smoke tracing under a blower door test shows it immediately.

Can you seal around windows without removing them?

Often yes, by detailing the internal perimeter and reveals. In some cases the trim is lifted to seal the junction properly. We assess each opening.

Do draughty windows cause mould?

The cold reveals around leaky openings frequently grow mould because they fall below dew point. Sealing and insulating the reveal addresses both the draught and the mould.

Should I keep my original sash windows?

Often yes — sash windows can be draught-proofed and refurbished to perform well while retaining character, which is frequently better value and more appropriate in period and conservation homes than wholesale replacement.

Is trickle ventilation enough once I seal the windows?

Trickle vents provide background ventilation but may not be sufficient once a home is well sealed. We assess whether trickle vents, continuous extract or MVHR is the right controlled ventilation to pair with the sealing.

Air leakage around windows and doors — the hidden draught.