SAP calculations in Greenwich

Conservation areas and the insulation you can actually fit

Greenwich has 23 conservation areas, and heritage at risk entries number 22. In a conservation area the usual energy upgrades meet resistance. Replacement windows may have to copy the original pattern, which limits the glass specification, and external wall insulation is often resisted where it would hide brickwork.

So the calculation leans on what can be changed quietly: roof insulation, floor insulation, airtightness and the heating system. We show building control exactly which elements were limited and why, because the guidance leaves room for reasonable provision in historic buildings.

A borough of renters, flats and some very large houses

Only 41.1 per cent of Greenwich households own their home, and 48.4 per cent live in a house at all. Conversions and flats are therefore a large part of the housing picture, as well as classic rear extensions.

Prices vary sharply: a terraced house averaged £545,565 while a detached one reached £1,009,528 in the latest Land Registry data. For a conversion into flats the assessment runs per dwelling, and each flat needs its own result, so the number of units drives the fee more than the building's size does.

Energy rules for a Greenwich extension

Extensions are measured against the limits 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. A flat roof or a mansard-style rear addition meets the roof figure with a thick warm deck.

The glazing rule has to be checked too: 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. When the design outgrows it, the guidance offers: Alternative routes: area-weighted U-value (para 10.9) or a SAP calculation against a notional extension (para 10.10).

Our construction drawings record every build-up, so the assessor models what the builder will construct and not a generic wall.

Conversions, new dwellings and the energy edition

A new flat or house is assessed against a notional building. 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 the plans go in decides which edition applies, and the transition note says: AD L/F 2021 continue where plans/notices are deposited before 24 Mar 2027 and work starts before 24 Mar 2028.

Flats in particular must watch summer comfort. Approved Document O (overheating) applies to new residential buildings. A top-floor flat with large windows facing the river side of the borough needs shading or opening areas that the assessor can see on the elevations.

Working with an assessor on a Greenwich conversion

Conversions in Greenwich often combine a protected facade with a modern interior. The assessor needs to know which walls are retained, which are new and how each one is insulated, because the retained masonry usually has a weaker U-value than the new build-up beside it.

We mark those walls on the plans in different hatches, so the model is built from what the drawing shows. Where a retained wall cannot be improved, the assessment compensates through the heating system, the roof and the ventilation, and we document the trade for the building control officer.

Timing matters too. The energy figures should be agreed before the building regulations package is submitted, so the notice carries the final specification and the officer does not ask for it halfway through the work.

Ask your contractor early whether they have installed the chosen insulation system before. A product fitted badly can lose much of its rated performance, and building control looks at workmanship on site as well as the paperwork.

Linking the energy work to your other Greenwich drawings

See the local picture at architectural drawings in Greenwich, and the technical layer at building regulations drawings in Greenwich. A loft addition adds its own energy question, which our loft conversion drawings in Greenwich answer at the design stage.

The energy work is a fixed quote after a free constraints check, VAT included. Send the address and the number of dwellings and we confirm the route.