Manchester and the North West hold some of the country’s finest Victorian and Edwardian stock, and every autumn their owners face the same question.
The windows rattle, the rooms are cold, and the quotes on the table run from a few hundred pounds to a full replacement. The useful answer is that most single-glazed timber windows can be made comfortable for winter without replacement, provided the work happens in the right order.
The heat leaves through the gaps, not the glass
Historic England’s research on traditional buildings is blunt. Older buildings lose 15 to 20 per cent of their heat to draughts, roughly a fifth of a home’s heating escapes through the windows, and most of that is air moving through gaps rather than heat conducting through the pane. Less than a quarter of a traditional timber window’s heat loss is the glass itself. The gaps are the cheap part of the problem, the glass the expensive one.
Repair before you seal
Seals fitted to a window that does not close properly are wasted money. Historic England put straightforward repairs alone, easing the sashes, closing open joints and renewing cords, at up to a third of a window’s air infiltration before a single seal goes in. The Society for the Protection of Ancient Buildings advise that when one sash cord breaks, all the cords on that window are worth replacing.
One caution before levering. A window painted or wedged shut for years may have taken on a structural role, and Historic England record cases of part of a wall collapsing when one was forced open. A sash that will not move is a job to look at, not to force.
The right seal for each surface
A simple rule sits under the product names: sliding surfaces need a wiper seal, meeting surfaces a compression seal, which is why one strip off a shelf rarely fixes a sash. The Energy Saving Trust is direct: for sliding sash windows, foam strips do not work well, and it is best to fit brush strips or consult a professional. Done properly, Historic England say air infiltration through a sash window in good condition can be reduced by as much as 86 per cent — a figure about air movement, not a saving on a bill.
One VAT quirk is worth putting to a contractor: draught stripping is zero-rated until 31 March 2027, while cord, pulley, rot and decoration work stays at 20 per cent. Scott James Sash Windows Specialists set out what the work involves window by window.
If you do want to deal with the glass
The expensive half of the problem has a middle option. Vacuum-insulated units around 8mm thick can be fitted into the existing sashes, so the frames, glazing bars and look of the window stay as they are, though the sashes usually need rebalancing for the heavier glass. Worked examples of reglazing single-glazed sashes are at https://scottjameswindows.co.uk/single-glazed-windows/, and thermal-camera comparisons of the result at https://chameleon-restoration.co.uk/thermal-imaging-double-glazing/.
What not to seal, and what to leave until Spring
Not every gap should be closed. Rooms with an open-flued fire, stove or boiler should not be draught proofed without specialist advice, and Historic England recommend older buildings run at 0.4 to 0.8 air changes an hour.
Where secondary glazing is already fitted, the window behind it is left alone: sealing both traps moisture in the cavity. Paint and putty are spring jobs needing dry weather, the flexible part of a seal should never be painted, and paint predating the 1992 UK ban should be assumed to contain lead and never dry-sanded.
