What causes draughts through closed windows and doors
There are several distinct causes, and identifying the right one matters - each requires a different repair.
Failed compression gaskets
The most common cause of persistent draughts through a closed frame. The rubber or foam gasket that runs around the opening edge of windows and doors is designed to compress and create an airtight seal when shut. Over time, gaskets harden, lose their profile, shrink at corners, or detach from the channel. Once compression is lost, air passes through freely.
This is the cause if the draught is consistent regardless of weather - if it's cold whether it's windy outside or not, gaskets are almost certainly involved.
Failed external perimeter sealant
The flexible bead running around the outside of the frame where it meets the masonry. When this cracks or lifts, gaps form between frame and wall. In windy conditions, air can be driven through these gaps into the reveal and appear to come through the frame. This tends to be more noticeable in windy conditions rather than simply cold ones.
Warped or distorted frames
Timber frames in particular can absorb moisture and distort over time, meaning they no longer close fully against the weatherseal. In this case, replacing the gasket alone won't fully resolve the problem - the frame may need adjustment. Aluminium and UPVC frames can also distort if poorly fitted originally, though this is less common.
Poor original installation
On some properties, particularly where windows have been replaced in the past, frames were never fitted with adequate perimeter sealing. There may never have been a proper joint between frame and masonry. This is worth checking on any property where the windows were replaced more than 15 years ago.
How to identify where the draught is coming from
Two simple methods work well for this:
- Hand test. On a cold or windy day, slowly move the flat of your hand around the closed frame - the perimeter between frame and masonry, and around the edge of the sash or door leaf. Where you feel cold air, that's where the seal has failed. The location tells you whether it's the external joint (gap between frame and wall) or the internal gasket (gap at the sash edge).
- Candle test. Hold a lit candle or lighter flame slowly around the same perimeter points. Movement in the flame indicates air movement. Do this carefully - the flame is for detection only, and should be kept well clear of anything flammable.
These tests help you describe the problem clearly before we attend, and they help us confirm the diagnosis on-site.
Energy efficiency and the real cost of draughts
Failed seals and gaskets have a direct financial impact. Cold air entering through frames means the heating system works harder to maintain room temperature - the heat you're paying for is leaking out through the same gaps the cold is coming in through.
On a typical semi-detached property with several windows showing draught failure, the annual heating cost increase can be meaningful. Gasket replacement and perimeter resealing are among the most cost-effective improvements a homeowner can make to the building fabric.
Why draught excluders and tape are not a solution
Temporary draught excluders - brush seals, foam tape, door snakes - address the symptom only and have a short lifespan. They also tend to interfere with the operation of windows and doors. The correct fix is to replace the component that has failed. A properly fitted gasket will last 15 to 25 years. A strip of foam tape around the frame will fail within a season or two.
The connection between draughts and condensation
Cold air entering around frames reduces the surface temperature of the inner reveal and glass. When warm, humid room air contacts these cold surfaces, condensation forms. This is why condensation appearing on window reveals or at frame edges is often caused by draught failure rather than general humidity. Addressing the draught reduces the cold surface temperature and usually reduces condensation in these locations.
The right repair for each cause
For failed gaskets : We remove the perished material and fit compatible replacement gaskets that restore correct compression. See our window and door seal replacement service for detail.
For failed external sealant : We fully remove the old bead and apply new sealant in the correct profile. See our external sealant replacement service for detail.
For warped frames or poor original installation: We assess what's needed - this may involve frame adjustment, new perimeter sealant, or in some cases recommending frame replacement if the frame itself is too far gone.