Two-Storey Extension in Belsize Park: Guide and Costs

A two-storey extension in Belsize Park provides double the additional space of a single-storey extension for significantly less than double the cost. By adding both a ground floor kitchen-diner and a first floor bedroom or bathroom, you can transform your Belsize Park home's functionality and value in a single project.

Design Considerations

Two-storey extensions in the Belsize Conservation Area require careful design. Camden Council expects extensions to be subordinate to the main building — set back from the existing rear wall at first floor level, with a lower ridge height than the main roof. Materials should complement the existing building, typically matching brick, with the option of contemporary detailing at ground floor level.

Ground Floor Options

The ground floor of a two-storey extension typically creates an open-plan kitchen-dining space. Large glazed doors and rooflights at ground level create a light, contemporary space that connects to the garden. The solid first floor above provides structure while the ground floor can be predominantly glazed.

First Floor Options

The first floor extension typically adds a new bedroom — often a master bedroom or children's bedroom — with an en-suite bathroom. Alternatively, the space can be used for a large family bathroom, a home office, or a dressing room. Windows at first floor level must be designed to avoid overlooking neighbouring properties.

Planning Permission

Two-storey extensions always require planning permission. In the Belsize Conservation Area, applications receive additional scrutiny. Key considerations include impact on neighbours' light and privacy, scale and massing in relation to the existing building, materials and architectural detailing, and effect on the conservation area's character.

Costs

A two-storey extension in Belsize Park typically costs £120,000 to £250,000 for building work, depending on size and specification. This represents significantly better value than building two separate single-storey projects, as the foundation, scaffolding, and roof are shared. Total project costs including kitchen, bathroom, and finishes can reach £180,000 to £350,000.

Timeline

A two-storey extension typically takes 12 to 18 weeks on site. Add 8-12 weeks for planning permission and 4-8 weeks for design and preparation. From initial concept to completion, allow 6-10 months.

Value Added

In Belsize Park, a two-storey extension adding a bedroom, bathroom, and enlarged kitchen can add 15-25% to a property's value — often representing a return of 150-200% on the investment.