Extension Permitted Development Calculator — PD Rights Check

For semi-detached and terraced houses, the maximum rear extension depth is 3m (or 6m with prior notification under the larger home extension scheme). For detached houses, the limits are 4m (or 8m with prior notification). These are measured from the original rear wall of the house. Conservation areas cannot use the larger extension scheme.

The larger home extension scheme allows deeper single-storey rear extensions under PD — up to 6m for semi/terraced and 8m for detached — subject to a prior notification process. You submit a notification to the council, who consult your neighbours. If no objections are raised within 42 days, you can proceed. This does not apply in conservation areas.

A single-storey rear extension must not exceed 4m in overall height (GPDO Class A.1(f)(ii) and, under the larger home extension scheme, A.1(g)(ii)). The extension's eaves must not exceed the eaves of the existing house (A.1(d)), and where any part of the extension is within 2m of a boundary the eaves are capped at 3m (A.1(i)). The extension must not be higher than the highest part of the existing roof (A.1(c)). Side extensions are limited to a single storey and a maximum height of 4m (A.1(j)).

PD rights are more restricted in conservation areas. Rear extensions are limited to 3m (semi/terraced) or 4m (detached) — the larger extension scheme does not apply. Side extensions and cladding are not permitted. Any extension visible from a highway may require planning permission. Always check with your local authority.

Yes. Permitted Development only removes the need for planning permission — it does not affect Building Regulations. All extensions must comply with Building Regulations (structure, insulation, ventilation, drainage, fire safety, electrics) and require a Building Regulations application and inspections.