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SAP Calculations

Part L compliance for new builds, conversions and extensions — from design-stage assessment through to the as-built calculation and on-construction EPC. Fast turnaround from drawings, and clear advice when a design needs help to pass.

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The essentials

What a SAP calculation actually is

SAP — the Standard Assessment Procedure — is the government's methodology for rating the energy performance of dwellings. It models the whole dwelling: fabric heat loss, thermal bridging, heating and hot water, ventilation, lighting and renewables.

For anything you're building, it answers the question building control will ask: does this dwelling comply with Part L of the Building Regulations? And for new homes it does one more job — the as-built SAP is what generates the on-construction EPC.

Part L compliance is demonstrated by meeting targets for emissions (TER), primary energy (TPER) and fabric efficiency (TFEE), plus minimum standards for each building element. A design-stage SAP must be submitted before work starts, and the as-built version reflects what was actually constructed.

The SAP process

  1. Design stage — we model the dwelling from your plans and specification, and issue the Part L report for building control.
  2. Design fixes (if needed) — if the first pass fails, we recommend the cheapest changes that get it through, and re-run at no drama.
  3. As-built — once construction is complete we update the model with any changes and the air test result.
  4. EPC lodged — the on-construction EPC is generated and lodged, ready for completion and sale.

Where SAP applies

SAP calculations for every project type

New build dwellings

Every new dwelling in England and Wales needs a SAP calculation — no exceptions. We work with self-builders on a single plot and with developers running multi-plot sites, providing design-stage reports for building control submission and as-built assessments with on-construction EPCs at completion.

What you get

  • Design-stage SAP report and Part L compliance documentation
  • Specification advice if the design doesn't pass first time
  • As-built SAP incorporating the air-pressure test result
  • On-construction EPC lodged for every plot

Good to know

  • Book at design stage — retrofitting a failed spec on site is expensive
  • Multi-plot developments priced per plot with volume discounts
  • We flag air-tightness targets early so your builder knows what to hit
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Conversions & change of use

Turning a barn, office, shop or house into one or more new dwellings is a material change of use under the Building Regulations — and it triggers SAP. Conversion projects are where good modelling earns its keep: existing fabric, mixed construction types and listed-building constraints all need handling intelligently rather than by the standard new-build recipe.

What you get

  • SAP assessment tailored to the existing fabric and proposed upgrades
  • U-value calculations for upgraded elements — done in-house
  • Practical advice where heritage or structure limits insulation options
  • EPCs for each new dwelling created

Good to know

  • Applies to barn conversions, office-to-residential, HMO splits into flats and similar projects
  • Pairs naturally with our U-value service for element upgrades
  • Early advice can save an entire re-design at building control stage
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Extensions

Most extensions comply through standard fabric U-values — but highly glazed designs (typically where glazing exceeds 25% of the new floor area) fail the simple route. That's where a SAP-based approach rescues the design: we model the whole dwelling before and after, and show building control the extension performs no worse than a notional compliant one.

What you get

  • Whole-dwelling SAP comparison to justify glazed designs
  • Compensatory measures worked out — better fabric, controls or renewables
  • Report formatted for your building control body

Good to know

  • Saves glass-heavy kitchen extensions and garden rooms that would otherwise be refused
  • Often needed alongside U-value calculations for the new elements
  • Send us your architect's drawings for a same-week assessment in most cases
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Common questions

SAP questions, answered

What do you need from me to start?

Scaled floor plans, elevations and sections, plus the construction specification — wall, floor and roof build-ups, window and door details, heating and hot water system, ventilation strategy and any renewables. If anything's missing we'll tell you before we start, not halfway through.

What happens if the design fails?

It's common on a first pass. We identify the most cost-effective fixes — a touch more insulation, better glazing, smarter heating controls, waste water heat recovery, or photovoltaics — and re-run the model until it passes. The goal is the cheapest compliant specification, not the most gold-plated one.

How fast can you turn a SAP calculation around?

For most single dwellings with complete drawings we return the design-stage assessment within days. Tell us your building control deadline when you enquire and we'll confirm timing with the quote.

Do I need an air-pressure test?

New dwellings need air-tightness testing, and the result feeds the as-built SAP. We'll tell you the target from the design-stage model so your builder knows what to achieve, and we can point you to testing when the build is ready.

Is SAP the same as an EPC?

They're linked: SAP is the calculation methodology, and for new homes the EPC is generated from the as-built SAP. Existing homes being sold or let get an EPC from a physical survey instead — see our EPC service.

Need a certificate or calculation sorted?

Tell us the property type and postcode — we'll come back with a fixed quote and the earliest available date.

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