Use glass to add light and bring the outside in

Ever wondered at the blocked-up window spaces you see in many Georgian houses across the country? These are all thanks to the 1691 Window Tax. To avoid the levy, those with more than seven windows in their house bricked them up instead.

It might have been called the Window Tax, but it was effectively a tax on light, and it is difficult to think of a more punishing tariff as us humans thrive on light. To this end, glass is an architectural staple, choose the right specification for your project and the opportunities are endless.

Be careful, though. While windows should make up at least 15 per cent of a room’s floor area to provide adequate light, if they constitute more than 25 per cent you will need an energy assessment of your home’s U-value (thermal performance), to get building regulation approval. Make your life easier by using low-emissive glass: double-glazed glass with a coating applied inside the cavity of the two panes. Th e coating works by  the heat we generate in buildings. Although low-emissive glass costs around 15 per cent more than ordinary glass, it can reduce heat loss by as much as 50 per cent.

Note also that although there are no set thermal rules on window size, Part L of the building regulations recommends using small north-facing windows. Again, the size of south-facing glazing has to take into account a range of factors, including the insulation performance of the glass and its thermal mass level. Coated double glazing has the same thermal properties as a nine-inch brick wall. And, as the good people of the late-seventeenth century could have told you, glass lets in a lot more light.

Useful Contacts

British Glass: www.britglass.org.uk
Colt Architectural Solutions: www.coltinfo.co.uk
FENSA industry body: www.fensa.co.uk
Guardian Industries: www.guardian.com
Interpane: www.interpane.co.uk
Optima Contracting: www.optima-group.co.uk
Pilkington: www.pilkington.com
Priva-lite: www.privalite.com
Saint Gobain: www.saint-gobain.com

Words: Karen Glaser