Your rooftop is a development site. Most freeholders never use it.

Airspace development is the construction of new residential units on top of existing buildings — effectively building a new floor (or floors) above a block of flats, house, or commercial property. It uses the “airspace” above a building that is already there, without requiring new land. In London, where land values are extreme, airspace development is increasingly used by freeholders and developers to add units and value to assets they already own.

Not always. Class AA permitted development rights allow additional storeys to be added above certain dwelling houses and blocks of flats without full planning permission, subject to prior approval from the local planning authority. Class AB covers commercial buildings. Prior approval is faster and less uncertain than a full planning application, though the local authority still assesses appearance, impact on residents, and other matters. RCB will confirm which route applies to your building and manage the process.

Airspace development typically starts from £80,000 per unit for a basic one-bedroom apartment above an existing flat roof, using lightweight steel frame construction. Costs vary with unit size, specification, access complexity, and the condition of the existing structure. The value of the completed units in London often significantly exceeds construction cost — which is why airspace development is so attractive for freeholders and developers.

Some disruption is unavoidable during structural works — particularly when the new steel frame is being erected. RCB sequences the programme specifically to minimise noise, dust, and access disruption to existing occupants. We use lightweight cold-formed steel frame construction which is faster and less invasive than traditional concrete or masonry. A resident communication plan is agreed before works start and maintained throughout.

Flat-roofed blocks of flats are the most straightforward — the existing roof is removed and the new steel frame rises from the existing structure. Purpose-built post-war residential blocks, 1960s and 1970s estates, and commercial buildings converted to residential are all common candidates. Buildings with strong foundations, solid structural walls, and existing lift or stair cores that can be extended are best suited. RCB will carry out a structural feasibility assessment before you commit.