Mumford & Wood’s double-glazed box sash window range has achieved a British Standards Institution A rating for its energy performance. Called Conservation, the range is designed to replicate the look of the original windows in older properties while offering good energy performance. The company says the range has an overall frame U-value of 1.4W/m2k which means it conforms to Part L. The windows are said to be almost indistinguishable from the original ones. They are made using traditional weights, brass pulley wheels and pre-stretched nylon cords. Glazing bar profiles include a choice of ovolo, lambs tongue and fine lambs tongue.