SAP calculations in Kensington and Chelsea

A borough of protected streets

Kensington and Chelsea has 39 conservation areas and 84 Article 4 directions. Historic England records 1,350 list entries, including 18 at Grade I.

For the energy design this has a plain meaning. Windows on a protected front cannot always be replaced with modern double glazing, and wall insulation outside is often off the table. A SAP calculation can show how much the rest of the building has to do to make up the shortfall, which is better than guessing. Approved Document L gives historic buildings special consideration, and we agree the approach early.

Where consent is needed for a window or a wall finish, we say so at the quote stage, so the energy design and the consent application tell the same story.

Trees, gardens and the shape of an extension

The borough publishes 4,560 tree preservation orders across 41 zones, and domestic gardens cover 17.5 per cent of the land. A rear extension rarely has room to grow, so each square metre of glass and insulation is worth designing.

For an existing house the starting point is the elemental route. The limiting values for new elements are: New elements in existing dwellings, limiting U-values W/(m²·K): roof 0.15, wall 0.18, floor 0.18, windows 1.4 (or WER Band B), doors 1.4. If a lightwell or glazed roof breaks the opening limit, the alternative is: Alternative routes: area-weighted U-value (para 10.9) or a SAP calculation against a notional extension (para 10.10).

Value, quality and why we calculate early

The average home here sold for £1,232,640, a terraced house for £2,429,086 and a flat for £971,688. Owners at this level rarely accept a poor result, and rebuilding an interior is a common project. Only 17 per cent of households live in a house, so many jobs are in flats and need the lease and the freeholder's agreement alongside the energy design.

The council grants most householder applications. It decided 664 in the latest year, granting 93.7 per cent, but only 91.9 per cent were decided in time, so build the timetable with margin. Those are householder figures only.

Because so many homes here are flats, we also ask early who owns the roof, the walls and the windows. A SAP calculation can only assume changes that the freeholder and the lease allow, and a design that depends on new insulation outside a leaseholder's own flat will not survive that question.

New homes and the standard that applies

A new dwelling, or one formed by rebuilding behind a retained facade, is assessed as a new home. The method is stated as: For new dwellings AD L 2026 names two methods: the Home Energy Model (HEM) and SAP; validity dates are in the Notice of Approval. An energy performance certificate follows: An energy performance certificate is required on construction of a new dwelling.

The standard also changes with time, so the date of your deposit matters: AD L 2026 takes effect 24 Mar 2027 (24 Sep 2027 for higher-risk building work). We confirm the position before pricing, and we draw the matching construction drawings in Kensington and Chelsea so that the specification and the calculation agree.

Where to go next

The wider picture is on architectural drawings in Kensington and Chelsea. For the energy rules on the borders, see SAP calculations in Westminster and SAP calculations in Hammersmith and Fulham.