Draughtproof a sash window

Fit brush and compression seals to a sash window to cut draughts, without disturbing the sash cords.

SW-01Check the window opens and prepare the areaOpen and close both sashes to check they run freely. If a sash is painted shut, deal with that first in the next step. Lay a dust sheet under the window and clear the sill, and have your tools and seals to hand — old paint and putty make a mess.

1 each · Dust sheet

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SW-02Free a sash that's painted shutRun a sharp craft knife along the paint line between the sash and the frame, on both sides and along the top and bottom. Tap a wood block gently against the sash with a hammer to break it free. Never lever directly on the glass or a thin glazing bar.

1 each · Craft knife

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1 each · Hammer

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SW-03Remove the staff beadSlide a filling knife behind the thin inner staff bead and gently prise it away from the frame along its length, starting at a corner. It's usually held by only a few small pins or old paint, so go slowly — you'll refit this same piece later. If your home is listed, check with your council's conservation officer before altering original window joinery.

RULES

1 each · Filling knife

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KNOW THE RULES

Listed buildings need Listed Building Consent for alterations to original windows, and this can include joinery work like removing beading. Check with your local conservation officer first if your home is listed.

SW-04Fit brush pile strip to the running channelsCut self-adhesive brush pile draught strip to length and press it into the channel where the sash slides, so the pile sits against the face of the sash. Fit it to both the outer channel (against the parting bead) and the inner channel (against the staff bead) on each side of the window.

2 each · Brush pile draught strip, 5m roll

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SW-05Refit the staff beadPush the staff bead back into place. If the old pin holes have failed, re-pin it with 25mm panel pins and sink the heads slightly with a nail punch. Slide the sash up and down to check it still moves smoothly with the new brush strip in place before moving on.

1 each · Panel pins, 25mm (pack)

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1 each · Nail punch

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SW-06Seal the meeting railFit a seal along the meeting rail — the horizontal bar where the top and bottom sashes overlap when closed. Pin or screw a compression or brush strip to the top edge of the lower sash's meeting rail so it presses against the upper sash when the window is shut.

1 each · Meeting rail draught seal

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1 each · Small screws, 12mm (pack)

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SW-07Seal the bottom rail and sash hornsFit a self-adhesive brush or foam strip along the underside of the bottom sash rail, where it meets the sill, and along any gaps at the sash horns. This is usually where you'll feel the strongest draught, so make sure the seal has full contact along its whole length.

1 each · Self-adhesive foam draught strip

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SW-08Fill the gap between the frame and the wallRake out any crumbling old putty or mortar between the outer timber frame and the masonry reveal. Run a bead of flexible decorator's caulk into the gap with a sealant gun and smooth it with a wet finger. Don't fill any weep holes or drainage gaps at the base of the frame — these let rainwater escape.

1 each · Flexible decorator's caulk, tube

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1 each · Sealant gun

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SW-09Lubricate, test and tidy upRub a candle or dry PTFE lubricant along the sash channels and cords so the sashes run smoothly against the new seals. Open and close the window fully several times to check it moves freely and closes tight. Vacuum up dust and offcuts and wash your hands — if the paintwork is original and the house was built before 1960, treat the dust as possibly containing lead and avoid dry sanding it.

1 each · Candle wax or PTFE lubricant spray

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