Most of Bradford’s older housing is built from the local sandstone with roofs of stone slate or, on later streets, Welsh slate. Stone slate is heavy and the rafters under it are often undersized by modern standards, so a Bradford survey spends longer in the loft than a Wakefield one. It is rarely a problem, but it is why the installer checks the structure before confirming how many panels go on a Great Horton, Eccleshill or Undercliffe terrace.
The hills matter as much as the stone. Bradford sits in a bowl and the suburbs climb out of it, so streets in Wibsey, Clayton, Queensbury and Idle have roofs at every orientation. Where the street runs east to west, the terraces have a south-facing pitch and take six to eight panels; where it runs north to south, both pitches face east and west, which still works at about 85% of the south-facing output. The 1930s semis in Thackley, Wrose, Bierley and Low Moor are the simplest roofs in the district.
The Aire valley towns, Shipley, Saltaire, Baildon, Bingley and Keighley, add a heritage dimension: Saltaire is a World Heritage Site with a buffer zone of more than a thousand hectares, and there are conservation areas in Little Germany, Ilkley, Haworth and the old village centres. The Victorian mill-workers’ terraces in Saltaire itself are listed, which rules out roof solar without consent; most houses in the buffer zone are not listed and can proceed with care.