SAP calculations in Lewisham

Small sites and the case for calculating early

A home added in a back garden or on an old garage plot is a new dwelling, and its energy case is a full assessment. For the method: For new dwellings AD L 2026 names two methods: the Home Energy Model (HEM) and SAP; validity dates are in the Notice of Approval. Domestic gardens cover 31.1 per cent of the borough's land, a high share, so there is real supply of such plots.

A new home also needs overheating checked: Approved Document O (overheating) applies to new residential buildings. On a tight site with neighbours close by, a large south-facing window needs shading, and that is easier to design in than to add afterwards.

Small sites also raise a practical point about who does what. We draw the scheme and brief the assessor with the full construction build-up, window schedule and heating assumptions. The assessor returns the numbers, and we adjust the drawings if the result shows a weak spot. One loop, finished before the building control submission, is far cheaper than two, and it avoids a redraw.

Extending a Lewisham house

Of Lewisham's households, 42.2 per cent live in a house, and a terraced house averaged £602,116 in the latest Land Registry figures. The common projects are rear and side extensions.

The elemental limits for new parts of an existing home 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. Glazing carries its own limit: 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 calculation gives you the freedom to exceed that if the rest of the building compensates.

Prior approval in Lewisham: a hard road for larger extensions

Lewisham's planning statistics show the larger home extension prior approval route is seldom successful here. In the latest year the council granted 2 and refused 46. By comparison it granted 89.4 per cent of ordinary householder applications.

That gap points to an approach. If a rear extension is large, a full householder application is usually the safer route, and the energy design can then follow the approved plans. The sequence matters because a late change to the footprint reopens the calculation. See our planning drawings in Lewisham for how we prepare those.

Heritage and Article 4 in Lewisham

The borough has 30 conservation areas and publishes 57 Article 4 directions across 89 areas. 367 list entries are recorded, including 2 at Grade I. These can remove rights that would otherwise apply, so we search them for your address before we choose a route.

Decisions are fairly prompt. Lewisham decided 578 householder applications in the year and 95.2 per cent were in time. Those figures cover householder applications only, so a small-site home will have its own, longer timetable with conditions to discharge, and the energy evidence is one of the documents building control will want on the file.

Related pages

The wider picture is on architectural drawings in Lewisham. The same service next door is covered in SAP calculations in Greenwich and SAP calculations in Southwark.