Proofing Sash Windows
Sash windows can be draughty, particularly older examples. In fact the total amount of escape of heat around a box sash window is equivalent to having a hole about 4” square to the outside world. Fitting double glazing alone, if its possible (and usually its not), will not materially make any difference when it comes to draughts or saving heat escaping. Even if double glazing can be fitted, the units may blow and fill with condensation, thus any financial gain will be lost when you have to replace them. Most new plastic window guarantees do not usually include the double glazed units for that very reason.
The answer is to improve the existing sash windows by replacing the staff and parting beads with new timber beads that have a brush pile fitted into pre cut grooves. There are other benefits beside proofing against draughts: there will be the reduction of outside noise migrating into your home and the elimination of rattle. If you add thick curtains, which really do work, then you can be assured of a snug, warm home without desecrating the appearance of a period-windowed property.
So how do I draught and rattle proof those sash windows, with the added benefit of sound reduction? To begin with, I remove the two sashes and fit replacement cords. It’s good practice to do this at the same time rather than reuse old cords. Often they may look fine and certainly work alright, but UV light will have weakened the section of the cord that is exposed to light. Cords, particularly the unwaxed ones often fitted in older windows, are prone to this weakening. At the same time I check the putty. If this is cracked, or has parted from the glass, it needs to be raked out and replaced. Putty that has failed is the number one cause of rot in wooden windows.
Once these two items have been attended to, the next thing to do is to machine out a 2mm groove on the meeting rail (the bottom rail of the top sash and the top rail of the bottom sash), and also to machine out a 2mm groove on the bottom rail that sits directly onto the cill. Into this groove a flexible seal is inserted. At this point I assess the gap between the edge of the window and the box; if this is slack then further grooves are machined along the edge of the window – the stiles – and a brush seal inserted. Finally, parting beads with pre-machined brush seals are fitted, reversing them at the meeting rail so that the brush sits against the face of each window. The staff beads with pre-machined brush seals are then fitted. The parting and staff beads are timber; plastic ones are available but they don’t quite look right.
Proofing Casement Windows.
The above mentioned issues with sash windows are common with casement windows as well. Modern (and by that I mean post 1970s) casements are often already fitted with an ‘aqua’ seal or at least the remnants of one. Often I see these windows with the groove machined to accept the seal but no seal. If it is the case that there is either no seal or a degraded one, then a replacement can be fitted without too much effort. If this is not the case, such as for pre 1970s casements, then a replacement window stop will need to be fitted, with the appropriate groove machined and the seal inserted. I can copy most mouldings found on window joinery so there should be no material difference between your old stops and replacement ones, although you will need to paint them. This may be important on period buildings, and insisted upon for listed buildings, or you may wish to simply keep the visual appearance the same.
At the same time as undertaking this work, I check the putty for defects and I also check the throat that should run around the whole casement. Often it is full of paint or missing. I have mentioned throating in another article on this website, but simply put its job is to prevent water sitting between the window and cill, which results in rot, and to prevent water being blown in during wet and windy weather. It’s simply a groove around 5mm wide and 3mm deep. The seal itself is available in white or brown and closes any gaps between 1 and 5mm.
Often I am asked to fit a replacement exterior door, usually the main entrance or back door, but sometimes full sets of French doors, because ‘this one is draughty’. The door itself is often perfectly adequate and in good condition. To reduce and possibly eliminate draughts, and therefore heat loss, one starts with the door frame. A brush seal is fitted to the frame which will close the gap between the door and the frame stops, not only reducing heat loss but also eliminating the daylight that you can often see along the edge of the door when it is closed, particularly on sunny days. A brush seal along the bottom of the door has the same effect. If the door stops are nailed or screwed onto the frame, these can be removed and replacement stops fitted, with a ‘aqua’ seal inserted into a machined-out groove, much the same as for casement windows as mentioned earlier. If the stops are part of the frame, and this is usually the case, then a groove can be machined around the edges of the door instead and a brush pile inserted – the same method that is employed in weather sealing box sash windows. This brush pile sits proud by about 1.5mm to 3mm. A combination of exterior draught excluder, brush pile or ‘aqua’, and bottom brush will have a massive impact on heat loss and reduce considerably noise from outside. A final weapon in the tool box is a letter plate draught excluder fitted over the letter plate aperture on the inside of the door.
So all in all, if you are fortunate enough to live in a property which has retained its original ‘pre-plastic’ windows and doors, it is not inevitable that you have to suffer draughts and high heating bills.