See our expert buyer's guide to replacement windows
Owners of listed buildings and those in conservation areas must consult a conservation officer before carrying out work that will change the appearance of their homes. Listed property owners must obtain Listed Building Consent before replacing windows, and many experts argue for repair rather than replacement. New fenestration in listed buildings must be in appropriate materials and in a sympathetic style. This normally means replicating the original period features as well as materials.
Rules for new and replacement windows now specify low-emissivity double glazing as standard and are stated in Part L (Conservation of Fuel and Power) of the 2006 Building Regulations available at www.planningportal.gov.uk. As the quest to improve energy efficiency continues, there will be further alterations to Part L in 2010 and 2013, culminating in zero-carbon homes by 2016. At present, energy efficiency grades for windows are similar to categories for white goods, running from A to G with A being the most efficient (see www.bfrc.org). Each window must have a Window Energy Rating (WER) of E or better, as stipulated by the British Fenestration Rating Council (BFRC). Energy efficiency can also be expressed by U-value. The standard U-value windows must achieve is 2.0 W/m2K (watts per sq metre lost).
Period property options
There are two solutions for increasing energy efficiency and soundproofing to period windows without standard double glazing. One solution is a sliding secondary glazing frame, but Ronnie Salisbury, former cabinetmaker and MD of The Sash Restoration Co, has developed a more effective option. His timber box sash unit is a slimline design, with each pane double glazed separately, virtually indistinguishable from its single-glazed counterpart. The design has Listed Building Consent to be incorporated in several Grade II-listed buildings.