On this house we were asked to design windows to reduce the noise of traffic in the bedrooms to as close to complete silence as possible. However, the replacement windows had to match the originals and we were not allowed to change away from single glazing.

We decided to manufacture all the windows to use 13mm thick Pilkington’s Optilam-Phon and, as the slightest draught will allow noise penetration, to redesign the weatherproofing to make them as near 100% airtight as possible. In the bedrooms we also manufactured separate double glazed opening secondary casement windows, which reduced noise intrusion through the windows to zero.

As Victorian glass was ~3mm thick and the glass we used is 13mm, the sashes were over 4 x the weight of the originals, which added enormous complications as the windows had to be traditional pulley & weight box sashes and we weren’t allowed to increase the size of the rebate. We overcame the problems by minimising the thickness of the timberwork around the weights and by custom making them to the exact shape to make use of every bit of that space.

The sound reduction glass isn’t normally used in traditional windows and linseed oil putty would destroy it, making it go milky, so all the glazing had to be carried out using a special, over-paintable mastic which is very difficult to finish.