Retrofit double glazing only partly resolves the issue

Although double glazing alone looks to improve the thermal performance of the glass component, this only resolves a small part of the issue. The conductivity of the existing window frames and the air gap between the double-glazing chamber greatly impacts on heat transfer.

Aluminium frames are a poor insulator, drawing an extraordinary amount of heat out of your home on a cold day or night. Coupled with this issue is that most older aluminium windows were not designed to house double-glazing and can only accommodate a very minimal double glazing chamber. The optimal glazing chamber gap is between 14-20mm – anything less than this and the double glazing becomes less effective and any benefit significantly compromised. 

Older timber frames given the period in which they were built are also not designed to carry the weight of double glazed units that are far heavier than single pane glass. This extreme weight load onto the sashes and large glass surfaces can create significant problems with future functionality. 

Typically many of the older timber windows were slim-line to reduce weight and struggle to support the adequate width in the sashes to accommodate effective double glazing. Because retrofitting timber sashes requires a larger cavity channel to be created in order to accommodate the double glazed unit, often the air gap between the double glazing is greatly compromised, resulting in less than optimal heat retention.