I have a house that is on three floors however the overall height of the house is only that of a two storey house as it is built on a steep slope. I am looking into build a rear single storey extension ( eaves height 3.6m height ) however as the layout of the house is unusual this means that the extension will extended into the third floor bathroom. My question is, what is classes an extension as one or two storeys, Is it the over all height or is it if it extends between two levels. Its hard to explain without a diagram :)

  • Peter Eade

    With permitted development you are allowed to extend 4m out from the rear of the existing house and up to 4m high. The extension can only be single storey and the roof must not be higher than the existing house roof. The datum where to two 4m measurements are taken from is where the ground meets the rear wall of the house, this is usually around150mm below DPC, if the ground slopes up or down away from that point it makes no difference.

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