Window draughts come from four common sources: failed compression seals between the sash and frame, gaps where the frame meets the wall, worn brush seals on sliding sash windows, and damaged or shrunken timber on older windows.
To identify the source, run your hand around the window edges on a cold day or pass a lit candle slowly along the perimeter - air movement gives the location away.
Most draughts can be fixed without replacing the window: replace perished rubber seals (a straightforward DIY job), apply caulk around the frame-to-wall gap, fit new brush seals to sash windows, or use removable secondary glazing for severe cases. If multiple seals have failed and the frame itself is warping, full window replacement becomes the better option.
A window is designed to be airtight when closed. Air leaks happen when one of the components that creates the seal fails or is damaged. Identifying the source is the first step - fixing the wrong thing wastes effort and does not stop the draught.
You cannot fix what you cannot locate. Use one of these three methods on a cold or windy day to pinpoint where air is getting in.
Run the back of your hand slowly around the inside edge of the window, top, sides, bottom about 5cm from the surface. Cold air movement is easy to feel, especially against the more sensitive back of the hand. Mark each location with a pencil dot or piece of tape.
Light a candle and hold it just inside the window perimeter, moving slowly around the edges. The flame will dance or smoke trail will deflect at the point of air entry. This is more sensitive than the hand test but requires care, keep the flame well away from curtains and never leave it unattended.
A smoke pencil (sold for HVAC testing) or even a stick of incense produces a thin smoke trail that is easily deflected by air movement. This is the most sensitive method and the safest, no open flame, and the smoke shows the direction as well as the location of the leak.
This is the most common cause and the most accessible DIY fix. Modern windows use either an EPDM rubber gasket or a thermoplastic elastomer (TPE) seal pressed into a groove on the sash or frame. When these harden, they lose the squish that creates the airtight closure.
Replacement seals are widely available and the job takes 20–30 minutes per window once you have done one.
Over time, the joint between the window frame and the surrounding masonry can develop gaps. This is especially common where original caulk or filler has shrunk or cracked, or where the original installation used an inadequate amount of sealant.
Acrylic sealant is paintable and works well for visible internal joints. Silicone is more durable but harder to paint over, better for external or hidden joints. Both produce a flexible seal that accommodates the small movements between the frame and the wall.
Sliding sash windows, the kind that move up and down with cords and weights, use brush seals where the sashes meet each other and where they slide against the frame. These can be replaced as a kit on most original Victorian and Edwardian sash windows.
Brush seal retrofit kits typically include slim aluminium channels routed into the existing timber, with bristle inserts.
The work usually requires removing the sashes, routing grooves into the timber, and refitting.
Most homeowners use a specialist sash window contractor, the result transforms the air-tightness of a period property without losing the original character.
If the timber itself is warped, split or shrunken, no amount of seal replacement will solve the draught. The sash is not closing against the frame correctly because the surfaces are not flat or parallel.
Small splits and shrinkage can be addressed by a competent joiner with timber epoxy filler and refinishing. This works for windows that are 80–90 percent sound and just have local damage. For windows with widespread timber damage — soft, multiple splits, warping, repair often takes as much effort as replacement and rarely restores full performance.
Sometimes you need to reduce draughts immediately without doing a proper repair. These fixes work in the short term until you can do the permanent fix.
Foam tape applied between the sash and the frame creates a temporary seal. It compresses slightly when the window closes and fills small gaps. Comes in widths from 3mm to 15mm. Works for one season; will need replacing each year because the foam compresses permanently after several closures.
Magnetic or clip-on secondary glazing panels fit on the inside of existing windows. They are typically a plastic film stretched on a frame, sized to fit the inner window reveal. They eliminate draughts because they form a sealed second barrier, and improve insulation as a side benefit. Removable in spring when not needed.
Floor-length thermal-lined curtains drawn against the window create a still air pocket that reduces the felt effect of draughts. They do not stop the air movement itself, but they prevent the cold air reaching the room. Useful as a short-term measure or a complement to seal fixes.
Some windows are beyond the point where repair makes sense. Signs that replacement is the better option:
Modern windows are built around durable seals and well-aligned frames. If your current windows have any of the above issues, the cumulative effort of patch repairs often equals or exceeds a proper replacement, with much better long-term results.
