Turning a barn, office or single house into new dwellings is a material change of use — and it triggers SAP under the Building Regulations. We model the existing fabric honestly, handle heritage constraints intelligently, and give building control the evidence it needs.
Change of use
A new build starts from a blank page: pick a specification, model it, done. A conversion starts from a building that already exists — solid stone walls of uncertain thickness, a suspended timber floor here and a concrete slab there, an extension from the 1970s bolted to a structure from the 1870s. Modelling that element by element, rather than forcing it through a new-build recipe, is the difference between a compliance case building control accepts and one it sends back.
The regulations don't demand the impossible from existing fabric, but they do demand reasonable provision — and the SAP is where you demonstrate it. We work through what each element can realistically be upgraded to, what the constraints genuinely rule out, and what the whole building achieves once the proposed works are in the model.
Two obligations, not one: the change of use itself triggers SAP evidence for building control, and every dwelling the project creates also needs its own EPC at completion. We produce both from the same assessment so neither becomes a last-minute scramble.
Project types
Character is the asset and the constraint: exposed stonework, timber frames and heritage or structural limits that rule out standard insulation build-ups. We model what the fabric can take, document what it can't, and keep the compliance case realistic — so the design that won planning is the design that gets built.
Commercial shells were never designed to be lived in: curtain-wall glazing, deep floor plates and services built for a nine-to-five occupancy. The SAP work maps each new flat's fabric, heating and ventilation individually, so a scheme of many dwellings produces a clean, per-unit compliance trail.
Splitting a house into self-contained flats makes each flat a dwelling in its own right — its own SAP evidence, its own heating and hot water arrangement, its own EPC. If the split is heading towards licensed shared housing instead, our HMO services cover that route from design to licence.
Get ahead of it
Almost every conversion problem we see was avoidable at drawing stage: an internal insulation build-up that steals too much floor area, a glazing specification the existing openings can't accommodate, a heating strategy that doesn't survive the flat split. Modelling the scheme before the building control submission catches these while they cost a revision, not a redesign.
Upgraded elements usually need their performance proved as well — our U-value calculation service handles the wall, floor and roof build-ups the SAP model depends on, in-house and from the same set of drawings.
Common questions
It depends on the number of dwellings being created and the complexity of the existing fabric — a single barn is a different job from an office block becoming twelve flats. Send your drawings and a description of the existing building via the quote form and we'll reply with a fixed quote, usually the same working day.
If the project creates one or more dwellings where there weren't any — a barn becoming a house, offices becoming flats, a house split into self-contained units — that is a material change of use under the Building Regulations, and building control will expect SAP evidence of compliance. If you're unsure whether your project qualifies, send the details and we'll tell you straight.
Heritage and structural constraints can legitimately limit how far elements can be upgraded, and the regulations recognise that: the requirement is reasonable provision, not the impossible. We model what the fabric can genuinely accommodate, document why further upgrades aren't feasible, and make the compliance case building control needs — rather than pretending the constraint isn't there.
Yes — every dwelling the conversion creates needs its own EPC at completion, and a house split into four flats needs four. Because the EPCs draw on the same assessment work, we produce them alongside the SAP so completion isn't held up waiting for certificates.
Before the building control submission, ideally while the specification is still being drawn up. On conversions the expensive mistakes are baked in early — an insulation build-up that doesn't fit the existing walls, or a heating layout that can't serve the flat split. Early modelling flags those while they're still lines on a drawing.
Tell us the property type and postcode — we'll come back with a fixed quote and the earliest available date.