SAP calculations in Hammersmith and Fulham

Few houses, high values

Only 24.6 per cent of households here live in a house, and 32.1 per cent own their home. Houses are scarce, and priced to match: a terraced house averaged £1,139,759 and a detached one £1,716,974 in the latest Land Registry data.

At those values owners tend to build to the best specification the planners allow. We can ask the assessor to model a higher-performance wall and window package against the minimum, so the owner sees what the extra spend buys before ordering anything.

How the council decides householder cases

The council granted 97.8 per cent of householder applications over 506 decisions in the latest twelve months, though only 79.8 per cent were decided within the statutory period or an agreed extension.

A high grant rate is a reason to design carefully, not a reason to relax. Conditions on materials can be attached, and a condition that changes a window or a wall finish can change the energy result after approval. We carry known conditions into the specification so the figures still hold.

The limits an extension must meet

The relevant document sets these values for new elements: 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. In a tight London plot the thickness of a wall build-up costs floor area, so we choose thin, high-performance insulation where the drawings need it.

The glazing cap is: 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. A wall of glass onto a small garden is popular here, and when it exceeds the cap the route becomes: Alternative routes: area-weighted U-value (para 10.9) or a SAP calculation against a notional extension (para 10.10).

We draw this into every rear extension drawings set so the glass area is known before the planning drawing is fixed.

New homes, conversions and the certificate

A new dwelling follows a separate route. For new dwellings AD L 2026 names two methods: the Home Energy Model (HEM) and SAP; validity dates are in the Notice of Approval. Conversions and mews-style infills are assessed on the edition that applies on the deposit date.

On completion the rule is: An energy performance certificate is required on construction of a new dwelling. We keep the design specification on the sheets so the certificate lines up with the prediction.

Small plots need precise figures

On a compact Hammersmith and Fulham plot, a few centimetres of wall thickness is a real loss of room. We therefore check each element against the limit before choosing the product, so you do not buy a thicker build-up than the limit demands.

The usual targets are the roof, where a warm deck allows slim high-performance boards, and the floor, where the insulation sits under the screed. Walls can often use a thinner board than the first quotation assumed.

Glazing is chosen last and checked against both the cap and the planning drawing. If the design needs a slim steel-framed door, we confirm its declared performance before the order goes in, because a thin frame is rarely the best insulator.

If you plan to sell within a few years, the certificate you receive at the end becomes part of the sale pack, and buyers can read it. A better-than-minimum result can help at that point.

Pulling the Hammersmith and Fulham package together

Our page on architectural drawings in Hammersmith and Fulham sets out the local constraints, and building regulations drawings in Hammersmith and Fulham shows the construction detail the assessor reads.

The energy work is a fixed quote after a free constraints check, VAT included. Send the address and the brief to begin.