Double Storey Extension Plans
Two-storey extension design, planning drawings and planning applications. Nationwide across England & Wales.
Double storey extension design
A double-storey extension adds new space on both the ground floor and first floor at the same time. This is generally more cost-effective per square metre than two separate single-storey extensions — and avoids the disruption of two separate projects. A two-storey extension typically adds a new room on each level: perhaps a kitchen-diner at ground floor and a bedroom with en-suite at first floor.
Double-storey extensions have tighter planning restrictions than single-storey. The 45-degree rule, impact on neighbouring properties, the relationship to the existing roof line and the impact on rear light are all carefully considered both in the design and in how the application is prepared.
Key design considerations
The 45-degree rule
Most planning authorities apply a 45-degree rule which limits the impact of a two-storey extension on the windows of adjoining properties. The design must address this from the outset.
Roof design
The roof of a double-storey extension has to relate well to the existing house roof. A poorly resolved roofline is a common reason for planning refusal or a cluttered result.
Staircase and first floor layout
Adding first floor space requires considering the staircase position, room layout and access. The design coordinates ground and first floor together.
Impact on neighbours
A double-storey extension has more potential impact on neighbouring properties than a single-storey. The design considers overlooking, loss of light and visual impact from neighbouring gardens and windows.
Planning permission is almost always required
Double-storey rear extensions are almost never Permitted Development — a full planning application is required in virtually all cases. We advise on the planning route and manage the full application process.
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