Free tool
Extension size visualiser
Adjust the width and depth to see the floor area a proposed extension would add, drawn to scale against the permitted development depth limits for your property type.
This tool is pure geometry — width times depth, times the number of storeys — so the floor area figure is exact for whatever dimensions you enter. It also overlays the standard and Larger Home Extension permitted development depth limits, so you can see at a glance whether a given depth is likely to need more than a standard application.
Floor area gained
12.0m² (129 ft²)
Standard permitted development depth limit (3m)
Larger Home Extension limit, with prior approval (6m)
Charcoal = existing house (drawn to a fixed reference size). Orange = the proposed extension, to scale. This is a geometry visualisation, not a survey or a planning drawing.
Next steps
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