To qualify as permitted development some household building work projects – notably extending a house – must not exceed limits to the volume being added. The rules are currently different in England and in Wales. In England, the volume allowance mostly applies to loft conversions. You can read more on the Planning Portal. The Portal has also developed a tool to help you calculate volume. In Wales, volume allowance currently has a more significant role in permitted development, particularly with: Conservatories Extensions Loft conversions Outbuildings