DOCUMENT L

Document L of Building Regulations
All replacement window installations in England & Wales are subject to BUILDING REGULATIONS. This regulation in particular affects the minimum levels of insulation that replacement windows must have when fitted in your home. Levels of insulation are measured as U values. The lower the U value, the better the insulation level. In future what we may have in the past have referred to as "normal" double-glazing - i.e. two pieces of glass separated by a spacer bar is very unlikely to conform to building regulations. To get the required level of insulation it's almost certain some sort of LOW E glass (typically Pilkington K in the UK - although there are other brands) will have to be used. It may also be necessary for the sealed double glazed units to be Gas Filled (probably Argon).