Loft and basement conversions in London

The type of conversion (rooflight, dormer, hip-to-gable, mansard), the strengthening the existing floor needs, where the staircase lands, whether an en-suite is included, and the finishes. A mansard costs more than a dormer because the roof is rebuilt; a hip-to-gable adds a wall of brickwork.

We quote every loft after measuring the roof and checking headroom. The quotation separates the structural work from the finishes, so you can see what is driving the cost and where choices can be made.

Most loft conversions in London houses are permitted development, provided the added roof space is no more than 40 cubic metres on a terraced house or 50 cubic metres on a semi-detached or detached house, the dormer sits on the rear or side roof slope and not the front, and materials are similar to the existing house. Flats, listed buildings and homes where an Article 4 direction applies need a planning application.

Every loft conversion needs building regulations approval, covering the new floor structure, the staircase, fire escape, insulation and roof windows. A lawful development certificate is worth obtaining for resale.

As a rule of thumb, you need at least 2.2 metres from the top of the ceiling joists to the underside of the ridge for a conversion to work without lowering ceilings below. Victorian and Edwardian houses with steep roofs usually have plenty; 1930s houses with shallower hipped roofs often need a hip-to-gable conversion to create usable space. We measure this at the first visit.

Whether you are converting an existing cellar or excavating new space is the biggest factor: converting existing vaults means waterproofing, a new floor, insulation and services, while a new dig means underpinning and structural work on a different scale. Ground conditions, drainage and access for removing spoil also matter.

Converting an existing cellar without changing the outside of the house does not normally need planning permission; new lightwells, listed buildings and full excavations do. All basements need building regulations approval, and most involve party wall notices. We advise on the route and quote after a site visit.