Newsletter 4th Quarter 2009
Sash Windows 'are green'

English Heritage study finds that traditional sash windows are ‘green’

Research for English Heritage by Glasgow Caledonian University has found that simple improvements to traditional sash windows can bring most up to modern standards. The research has shown that original sash windows can be as energy efficient as modern double-glazed windows. Chris Wood of EH said ‘There is a lot of misunderstanding about the potential for historic buildings to be brought up to date. We hope this research will herald serious rethinking, and help homeowners and local authorities refurbish historic buildings with the confidence that modern standards can be met without compromising historic character.’

The key findings of the research include:

Air infiltration through a sash window in good condition can be reduced by as much as 86% by adding draught proofing.

Heat loss through contact with the glass and frames can be significantly reduced by thick curtains and plain roller blinds. In the test, heat loss was reduced by 41% and 38%, respectively.

More elaborate measures reduce heat loss even more and can improve windows to meet modern building regulations, which target a U-value for windows of 2W/m_K or below. In a test with good quality secondary glazing, this value was brought down to 1.7W/m_K. Well-fitted internal shutters also produce similarly good results. Using the methods in combination resulted in a 62% reduction in heat loss and a U-value of 1.6W/m_K, well in excess of even the most stringent regulations for newbuild and conversions.

Calculations on the carbon footprint of manufacturing new double-glazed plastic windows have shown that it would take 100 years for new plastic windows to repay the ‘carbon debt’ of their manufacture. As such windows only have a maximum life of 30 years and cannot be recycled, they clearly consume more energy than they save and will ultimately only add to the country’s problems with the disposal of toxic waste. Add to this the fact that estate agents value houses with original sash windows more highly than ones with plastic replacements and one realises just how big a turkey we have been sold by the doubleglazing industry.