Roof height on rear extension on sloping land

Updated on 16th November 2020 in Permitted Development
0 on 16th November 2020

Hi All,

I’m planning a single storey rear extension on my 1930s terraced house – 4.5m deep, full width of the house – 6m.

The house is on naturally sloping land, higher at the front. At the back of the house, there is a 0.7m drop to the patio and then a 0.4m drop to the original ground level (at the point of where the back of the extension will be).

The extension comes under permitted development if the height of the roof does not exceed 4m, measured from the “original ground level”.

Does anyone know where the original ground level is measured from? Is it the original ground level at the back of the original house? At the back of the planned extension? At the front of the house? From the patio level?

I’m planning on a flat roof and keen to ensure that I stay within permitted development.


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