Every new dwelling in England & Wales needs a SAP calculation to comply with Part L — submitted at design stage before work starts, updated as-built at completion, and finished with the on-construction EPC. We handle the whole sequence, and the fixes in between.
Part L targets
Part L doesn't set a single pass mark — it sets a notional dwelling of the same size and shape as yours, built to a reference specification, and derives targets from it. Your design has to beat those targets on three fronts at once, while every individual element also meets its own minimum standard, so a weak wall can't hide behind a generous solar array.
The design-stage SAP is the document that demonstrates all of this to building control, and it must be submitted before work starts on site. Get it done early and it becomes a design tool rather than a hurdle: the model tells you exactly which specification choices are doing the work, and which are dead weight you're paying for without needing.
Flag air-tightness early. The design-stage model assumes an air-permeability figure that the finished building must live up to under test. We state the target plainly in our reports so your builder knows the standard to build to — long before the fans arrive for the air-pressure test.
| Target | What it limits |
|---|---|
| TER | Target Emission Rate — the dwelling's CO2 emissions |
| TPER | Target Primary Energy Rate — the primary energy the dwelling consumes |
| TFEE | Target Fabric Energy Efficiency — how well the fabric itself performs, before systems help |
Plus minimum standards for each element — walls, roof, floor, windows, doors and air-tightness.
The process
Scaled plans, elevations and sections, plus the intended build-ups, glazing, heating, ventilation and any renewables. We confirm anything missing before modelling starts.
We model the dwelling against its notional targets and issue the design-stage report for building control if it passes.
A failed first pass is normal, not a crisis. We rank the options — insulation, glazing, controls, waste water heat recovery, photovoltaics — by cost against effect, and re-run until the design passes without gold-plating.
After construction, the model is updated with any on-site changes and the measured air-pressure test result.
The new build EPC is generated from the as-built SAP and lodged for each plot — the last document building control and the buyer's solicitor need.
Who we work with
Building your own home usually means learning Part L for the first time, mid-project. We translate the report into decisions: which specification upgrades are worth the money, what the air-tightness target means for your builder, and what to do in what order. You get one point of contact from first drawings to the lodged EPC.
Repeated house types are modelled once and applied across the site, with per-plot as-built assessments and EPCs lodged as each plot completes. We track the site as a schedule — which plots are at design stage, which await air tests, which are lodged — so nothing surfaces as a surprise at completion.
Related services: element build-ups that need proving are covered by our U-value calculations, converting an existing building instead falls under SAP for conversions, and a glass-heavy addition to an existing home needs SAP for extensions.
Common questions
It depends on the number of plots, the number of distinct house types and how complete the drawings and specification are. A single self-build is priced differently from a site with repeated house types. Send your plans and plot schedule via the quote form and we'll reply with a fixed quote, usually the same working day.
Before work starts on site — the design-stage SAP has to be submitted to building control at that point anyway, and it is far cheaper to fix a specification on paper than in brickwork. Booking early also means the air-tightness target reaches your builder while it can still influence how they build.
Nothing unusual — a failed first pass is a normal part of the process. We identify the cheapest combination of changes that gets the dwelling through: typically a step up in insulation or glazing, better heating controls, waste water heat recovery or photovoltaics. We re-run the model with each option costed against its effect, so you pass without over-specifying.
The as-built SAP must use the measured air-permeability result, not the design assumption. A build that leaks more than the design-stage model assumed can drag the dwelling below its targets, which is why we flag the air-tightness target to your builder early — hitting it on the first test avoids remedial sealing and a re-test.
Yes — for a new dwelling the on-construction EPC is generated directly from the as-built SAP, so there is no separate survey. We lodge the certificate for each plot once the as-built assessment is complete, ready for building control sign-off and the buyer's solicitor.
Tell us the property type and postcode — we'll come back with a fixed quote and the earliest available date.