Basement Conversion Drawings in Hammersmith and Fulham

Converting an existing cellar to habitable space in Hammersmith and Fulham 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. Hammersmith and Fulham does not have a borough-specific basement policy beyond the national framework — basement conversions are generally permissible subject to structural, drainage and flood-risk considerations. Thames Water Build Over Agreements apply where you're within 3m of a public sewer.

Our fixed-fee architectural package for a Hammersmith and Fulham basement starts at £1,950 (planning + building regs + structural + waterproofing specification). Build costs in Hammersmith and Fulham 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 Hammersmith and Fulham 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 Hammersmith and Fulham 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 Hammersmith and Fulham, 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 Hammersmith and Fulham 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.