Basement extensions have become popular with those looking to optimise space in their home, particularly in higher-value areas where the additional complication and cost of building below ground level is justified. It’s also a good option where constraints around the site or planning restrictions limit other opportunities to add more space.
Options include converting or extending an existing cellar or basement, adding new space by excavating beneath the existing property or garden, and even building under the pavement or road, subject to highways consent. Basement extensions can be two or more storeys deep, although the construction cost per square metre increases the deeper you go.
The new floorspace – a lower ground floor – is ideally located to provide additional living space, closely linked to the other ground-floor living rooms, but can also be used to provide additional bedroom accommodation subject to compliance with the Building Regulations, especially ensuring that all habitable rooms have windows for ventilation and a safe means of fire escape.
Spaces with lightwells or a sunken terrace are ideal for a family room, entertainment room, or guest bedroom. Basement rooms in the core of the house, with limited or no daylight, lend themselves better for use as a utility room, laundry room, cloakroom, plant room or storage.
Many basement extensions can be constructed under Permitted Development rights — subject to compliance with the rules, which you can find at . You could even create a separate basement flat underneath your home, but be aware that an independent self-contained dwelling will always require planning
