SAP calculations in Kingston upon Thames

Big plots, big extensions, big glass

Domestic gardens cover 30.9 per cent of the land in the borough, a high share, and 61.5 per cent of households live in a house. Owners here have room to build out and up, and bifold doors across a new rear wall are a regular request.

Large openings are exactly what the energy rules limit. The guidance says: Windows, roof windows, rooflights and doors in an extension should not exceed 25% of the extension floor area plus the area of openings removed or covered. If the design goes beyond that, the document offers: Alternative routes: area-weighted U-value (para 10.9) or a SAP calculation against a notional extension (para 10.10). A calculation can let a generous glazed wall stand if the roof and floor are better than the minimum.

A calculation also helps with the roof. Many Kingston houses are extended at the back and loft in the same project, and the energy sums for the new roof are different from those for the new walls. We run the whole building once, so the loft insulation and the rear glazing are weighed together, not in two separate rounds that contradict each other.

The result is one set of numbers the building control surveyor can check against the drawings, which shortens the questions that come back.

Prior approval for larger rear extensions in Kingston

The council's statistics show that bigger single-storey extensions are rarely approved through prior approval. In the latest year it granted 3 and refused 35. The route exists, but the outcome here often goes against the applicant.

Our usual advice is to decide the route before the energy design, because a householder application gives more room for a larger design. Our house extension drawings in Kingston upon Thames are drawn to suit whichever route applies, with the energy information alongside.

Protected areas, trees and the constraints check

Kingston has 28 conservation areas and 3 Article 4 directions, which cover 114 separate mapped areas. The council records 7,145 tree preservation zones, and 17 per cent of the borough is Green Belt.

We search all of these for your address. A Green Belt site changes how large an extension can be, and a tree zone changes where it can sit. Either one can change the glazing and insulation sums, so they come first in our free check.

Where a site lies in the Green Belt, the size of the extension is limited by that policy first. On a smaller infill plot the question changes to the neighbours and the daylight, and we handle that on the planning drawings rather than in the energy report.

Prices, decisions and timing

The average home sold for £591,555, and a detached house for £1,304,915. Kingston decided 742 householder applications in the latest year, granting 83 per cent and deciding 92.5 per cent in time.

For a new home, the energy method is: For new dwellings AD L 2026 names two methods: the Home Energy Model (HEM) and SAP; validity dates are in the Notice of Approval. The date that governs which standard applies to you is: AD L 2026 takes effect 24 Mar 2027 (24 Sep 2027 for higher-risk building work). We confirm it against your deposit date and link it to the building regulations drawings in Kingston upon Thames.

Nearby and related

The broader borough picture is on architectural drawings in Kingston upon Thames. Next door, see SAP calculations in Richmond upon Thames and SAP calculations in Merton.