SAP calculations in Hillingdon

Hillingdon's heritage is large and spread out

Historic England lists 436 entries here, 29 of them Grade II*, and the Heritage at Risk Register carries 45 entries. Registered parks and gardens number 2, and 5 scheduled monuments sit in the borough.

Some older listed buildings have solid walls, where cavity insulation is impossible and external insulation may not be acceptable. Approved Document L treats such buildings as special cases, where the aim is improvement as far as is reasonably practicable, so we agree with building control which measures are sensible and record them in the notes.

A busy planning desk

Hillingdon decided 1,147 householder applications in the latest twelve months and granted 90.2 per cent, with 94.3 per cent decided in time.

A materials condition on a roof or window can alter the energy inputs after the decision. We read the decision notice before finalising the calculation, so the figures describe the building as consented.

Housing stock and budgets

Around 68.9 per cent of households live in a house and 56.6 per cent are owner-occupiers. A terraced house averaged £457,686 and a detached one £941,938 in the latest Land Registry data.

At terraced prices the simple route is the usual answer. For detached houses and conversions, a fuller model lets the designer keep large openings without losing compliance.

What an extension must achieve

New elements are held to: 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 is separately limited: 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 conservatory-style room or a glazed link to a barn conversion is where the cap bites, and the guidance responds: Alternative routes: area-weighted U-value (para 10.9) or a SAP calculation against a notional extension (para 10.10).

For loft work, our loft conversion drawings in Hillingdon count roof windows into the same glazing total.

Hillingdon projects that need extra care

Some Hillingdon jobs sit between planning categories. A barn conversion, an annexe or a garden building used as a home can all be treated as a dwelling for energy purposes, even when planning calls them something else. We check how the building control team classes it before running any model.

The same applies to a change of use. Turning an outbuilding into living space brings the full set of energy standards, and the existing fabric may fall well short. Knowing that early lets you budget for insulation that was not in the original idea.

Tell us the use you intend and the state of the existing walls and roof, and we confirm which standard applies and what it will take to meet it.

Because Hillingdon projects vary so much, we also ask at the start how the heating will be controlled across the old and new parts, since a shared system changes what the assessor models.

New dwellings, barn conversions and the rest of the package

A new home or a conversion to residential use is assessed as a dwelling. For new dwellings AD L 2026 names two methods: the Home Energy Model (HEM) and SAP; validity dates are in the Notice of Approval. On completion: An energy performance certificate is required on construction of a new dwelling.

Read architectural drawings in Hillingdon for the planning context and building regulations drawings in Hillingdon for the technical set. Structural work follows in structural calculations in Hillingdon.

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