Original wooden sash windows are beautiful, authentic, and really look the part in your home. But, in many cases, they are draughty and noisy. Both the wooden sash window itself can rattle in high winds and they let in most of the sounds from outside – not ideal if you live on a busy street. So upgrading your existing wooden sash windows seems like a great idea, certainly better than replacing them with uPVC casements. But can you really double glaze original wooden sash windows?
Wooden sash window frame condition
The main challenge to overcome with replacing the existing glass in your wooden sash windows with double glazed sealed units is the frame. If the frames are as old your house, they could be damaged or warped and may need repairing or glazing bars replacing to accommodate the modern glass.
However, even if the frame is in good repair, you still might be facing a difficult task. The glass used in original wooden sash windows is very thin – probably under 4mm. This is not helping your thermal insulation at all, but also means that double glazed units, that come in at least 20mm, won’t sit in the grooves left by the original glass. You can try to route out the wood, but you risk damaging the frame, or there might simply not be enough wood to work with. There are slimmer sealed units, however costs and benefits analysis show that this investment is not the most cost/benefit effective as they do not add enough energy efficiency to justify costs.
Counterweight operation
If you’re lucky to have a counterweight system that works as new, then you’ll know that the weights match the weight of the wooden sash window perfectly to make raising the lowering the window easy and to hold the window open at any point. If you replace the original glass with double glazed units, the window will be much heavier, and you’ll have to replace the counterweights accordingly. If you don’t, then you’ll struggle to open the windows and you’ll have to use an additional fixture to hold them open.
However, what’s more likely is that the counterweight system is worn, and years of painting means that the windows are difficult to open anyway.
Perhaps another point to consider is that even if you’re successful in replacing the glass with modern double glazed units, and you’ve upgraded the counterweights, you might not have the warmth and sound-proofing you were aiming for. While it’s true that the glass in original wooden sash windows is very thin and a poor insulator, much of the draught and sound comes through gaps in the frame itself. So, your ill-fitting rattly frame will still be ill-fitting and rattly, letting in traffic noise and cold air after you’ve spent a lot of money replacing the glass.
Replacement wooden sash windows
Therefore, realistically, the answer to the question ‘can you double glaze existing wooden sash windows?’ is probably not. You can have a go, but most window companies will try to steer you towards replacements or proceed at an ‘at your own risk’ type arrangement.
Replacement windows will come with guarantees, and you’re going to end up with a warmer, quieter home that’s going to be more comfortable and energy efficient.
And the good news is that you don’t even have to compromise on the look. Yes, you can buy uPVC casements and even uPVC sash windows, but the best option to keep the character of your home is to replace with new wooden sash windows. You’ll get all the performance and keep the aesthetics of your period home.
Wood sash windows from Woodcraft Windows
At Woodcraft Windows we specialise in crafting bespoke wooden windows for period properties.
