Basement Conversion Drawings in Kensington and Chelsea

Converting an existing cellar to habitable space in Kensington and Chelsea usually does not require planning permission — it is an internal alteration. However, excavating a new basement, adding lightwells, or lowering floor levels to create a new storey typically does require planning. Kensington and Chelsea has a specific basement policy. RBKC's basement policy (post-2015) limits to single-storey under 50% of garden area; double-storey basements effectively prohibited in residential streets.

Our fixed-fee architectural package for a Kensington and Chelsea basement starts at £1,950 (planning + building regs + structural + waterproofing specification). Build costs in Kensington and Chelsea range from £3,000–£5,000 per square metre — a typical 40m² basement is £120,000–£200,000 to construct. Costs are higher than extensions due to underpinning, waterproofing and temporary works.

Most properties in Kensington and Chelsea can support a basement conversion, provided foundations are deep enough or can be underpinned, the water table is manageable, and there are no significant tree root or drainage constraints. Victorian and Edwardian houses in Kensington and Chelsea often have existing cellars that can be deepened. We assess suitability at the initial survey.

BS 8102:2022 requires a waterproofing strategy appropriate to the site's water table and ground conditions. In Kensington and Chelsea, this typically means a Type C cavity drain membrane system (most reliable), sometimes combined with Type A barrier protection. The strategy must be specified by a qualified waterproofing designer — included in our package.

A typical Kensington and Chelsea basement conversion takes 6–12 months to build once drawings are approved. Our architectural package takes 5–8 weeks from instruction to Building Control submission. The longer build time reflects the sequential underpinning process, which must proceed in careful stages.