What is the difference between a SAP calculation and a planning energy statement?

A SAP calculation satisfies the Building Regulations; a planning energy statement satisfies planning policy. They're required at different stages, by different authorities, and many residential projects need both.

Do I need a SAP calculation for an extension?

Sometimes. Under Approved Document L, the total area of windows, roof windows, rooflights and doors in an extension should not exceed 25% of the extension's floor area, plus the area of any windows and doors that no longer exist or are no longer exposed because of the extension. Stay within that, meet the standard U-values for the new elements, and the extension complies directly, with no SAP or area-weighted calculation needed. Where a design goes beyond that, the same paragraph can instead be satisfied one of two other ways: an area-weighted average U-value calculation, showing the extension's thermal elements average no worse than a compliant extension of the same size and shape, or a whole-dwelling SAP calculation, showing the dwelling plus the proposed extension performs no worse than the dwelling plus a notional compliant extension on primary energy, emission and fabric energy efficiency. SAP is usually the more flexible of the two, because the extra glazing can be offset by upgrades elsewhere in the existing dwelling rather than only within the extension itself. A conservatory or porch is generally exempt where it meets the conditions in paragraph 0.14.

Do I need a SAP calculation for a conversion?

Yes, where the work creates a new dwelling. The Building Regulations treat this in two ways: a material change of use, where a building becomes a dwelling, gains a flat, or changes the number of dwellings it contains, and a change of energy status, where a previously unheated space becomes part of the heated dwelling, such as a loft or garage conversion. Either route requires the work to meet the energy efficiency standards for existing dwellings: existing thermal elements brought up to the limiting standards, new and replaced elements to the standards for new work, and the openings in the new dwelling kept within 25% of its floor area. Where a building contains more than one dwelling, a SAP calculation can be used instead, to show the converted building's primary energy use and total emissions are no worse than if each dwelling had been improved element by element.

Why do SAP calculations fail?

Most avoidable fails come down to unassessed thermal bridging left on SAP's conservative default psi values, which alone can push a sound design over its primary energy, emission and fabric energy efficiency targets. Others: a glazing specification the fabric can't carry, or a heating and ventilation spec that undershoots the target. Caught at design stage, all three are a specification change. Caught after work starts, they're a site problem. Revisions are included until the design meets its targets.

When does the Future Homes Standard come into force?

Its Approved Documents were published 24 March 2026. The regulations come into force 24 March 2027, with a 12-month transitional period to 24 March 2028. A building control application submitted before 24 March 2027, with work commenced before 24 March 2028, can still be built to Part L 2021.

What calculation method applies under the Future Homes Standard?

The government has confirmed two methods for demonstrating FHS compliance during a phased transition. SAP 10.3 is an updated SAP 10.2, with a revised notional dwelling and carbon factors, available as the interim route. The Home Energy Model (HEM) is the longer-term replacement the industry is moving to. We work in SAP 10.3 now.

SAP Calculations — New Builds & Extensions | CCW Surveys

SAP Calculations

A SAP calculation shows that a new dwelling meets Part L of the Building Regulations. It runs in two stages. The Design Stage SAP is prepared at the technical design stage, before work begins on site, and demonstrates that the design can meet Part L. The As Built SAP follows on completion, produced from what was actually built and the evidence supporting it, and it generates the property's Energy Performance Certificate (EPC).

It is not the same document as a planning energy statement. A SAP calculation answers to the Building Regulations; an energy statement answers to a council's planning policy. Many residential projects need both. [How the two differ, and how we write energy statements → Energy Statements]

You work directly with Abbas Naji, our Elmhurst-accredited On Construction Domestic Energy Assessor (OCDEA, registration BH51-0001), the accreditation Building Control requires to produce a new-build SAP and lodge its EPC.

The compliance problem

The Design Stage SAP is a Building Regulations requirement, submitted to Building Control before work begins on site. It models the design against a notional dwelling of the same size, shape and orientation, built to a defined reference specification, which sets the three targets the design has to meet: the Target Primary Energy Rate (TPER), the Target Emission Rate (TER) for carbon, and the Target Fabric Energy Efficiency (TFEE).

Compliance is met on all three simultaneously, not as an average across them. The dwelling's own calculated figures must each come in no worse than the target it is set: DPER no greater than TPER, DER no greater than TER, DFEE no greater than TFEE. Limiting fabric and services standards sit underneath as backstops, so a strong result on one metric cannot rescue a wall U-value or a junction detail that falls below the minimum.

A shortfall against any of the three costs little to resolve on the drawing board. Once the specification is fixed, or work has begun, the same shortfall means revised glazing, a changed heating system or an altered wall build-up: a redesign at the worst point to be doing one.

The point at which an assessor is most useful is the design stage, before those choices are locked. Bringing the OCDEA in early does not change what the SAP is for. It changes how much room there is to reach compliance the efficient way rather than the costly one.

What we do differently

A SAP result is only as good as the assumptions behind it. Every U-value, junction and system efficiency is an input, and each input has a default the software will accept if no one examines it. We examine each one, checked against the specification and the design in front of us. On a tight Part L target, that is what decides whether a sound design passes.

Thermal bridging is the clearest example. Junction heat loss, at window reveals, wall-to-floor and wall-to-roof junctions, feeds directly into the transmission heat loss coefficient. Unassessed, SAP applies a conservative default in its place, and that default alone can push a design past its primary energy, emission and fabric energy efficiency targets, on a specification that is otherwise sound.

Corrected at design stage, this costs nothing to act on. Found at the As Built stage, the same correction is a site problem. That is what the rigour is for: a design that meets its targets on the specification it actually needs.

What you receive

For a new dwelling, the compliance set is:

● Design Stage SAP. The assessment that has to be in place before work starts, tested against the primary energy, emission and fabric targets.

● As Built SAP. The completion-stage assessment, updated for what was actually built and any changes made during construction.

● BREL report. The Building Regulations England Part L compliance report Building Control checks the build against.

● New-build EPC. Lodged on completion from the As Built SAP. The EPC is the SAP's output, not a separate exercise.

Extensions. An extension can need a SAP calculation too. The trigger is glazing: if the glazed area is more than 25% of the extension's floor area, plus the area of any windows and doors the extension covers over, the extension has to show compliance by calculation rather than by the standard elemental route. SAP is one of the two routes, and usually the more flexible one. The full rule, and the caveats, are in the FAQ below.

Conversions and change of use. Turning an existing building into a dwelling, a barn conversion, a commercial unit to residential, or a house divided into flats, also needs SAP calculations and an EPC. The compliance route differs from a new build; the FAQ below sets out how.

How we work

SAP is a desk-based assessment. We work from architectural drawings, elevations and sections, the construction specification, and the heating and ventilation details. No site visit is required, at design stage or as built; the As Built assessment is completed from photographic evidence and air testing, not a physical inspection. While based in Berkshire, we provide SAP calculations nationally. Design Stage SAP is returned within 3 to 5 working days of receiving a complete set of drawings and specification. We also work as a named sub-consultant to architects and consultancies who need SAP capacity behind their own client relationship.

Future Homes Standard readiness

We have the capabilities to work in SAP 10.3. If your scheme sits near the transition, or you want to know how a current design would perform against the Future Homes Standard rather than only today's targets, we can run it and show you the result. It is your design, your numbers, and the specific gap between the standard you are building to and the one coming next.

Get a tailored quote

Upload your architectural drawings and specification for a quote and delivery timeframe.

Frequently asked questions

A SAP calculation satisfies the Building Regulations; a planning energy statement satisfies planning policy. They're required at different stages, by different authorities, and many residential projects need both. [How we write energy statements → Energy Statements]
Yes, for a new dwelling. The Design Stage SAP is submitted before work begins and shows the design can meet the target primary energy, emission and fabric energy efficiency rates. The As Built SAP follows on completion, from photographic evidence and air testing, and generates the EPC.
Sometimes. Under Approved Document L, the total area of windows, roof windows, rooflights and doors in an extension should not exceed 25% of the extension's floor area, plus the area of any windows and doors that no longer exist or are no longer exposed because of the extension. Stay within that, meet the standard U-values for the new elements, and the extension complies directly, with no SAP or area-weighted calculation needed.
Where a design goes beyond that, the same paragraph can instead be satisfied one of two other ways: an area-weighted average U-value calculation, showing the extension's thermal elements average no worse than a compliant extension of the same size and shape, or a whole-dwelling SAP calculation, showing the dwelling plus the proposed extension performs no worse than the dwelling plus a notional compliant extension on primary energy, emission and fabric energy efficiency. SAP is usually the more flexible of the two, because the extra glazing can be offset by upgrades elsewhere in the existing dwelling rather than only within the extension itself. A conservatory or porch is generally exempt where it meets the conditions in paragraph 0.14.
Yes, where the work creates a new dwelling. The Building Regulations treat this in two ways: a material change of use, where a building becomes a dwelling, gains a flat, or changes the number of dwellings it contains, and a change of energy status, where a previously unheated space becomes part of the heated dwelling, such as a loft or garage conversion. Either route requires the work to meet the energy efficiency standards for existing dwellings: existing thermal elements brought up to the limiting standards, new and replaced elements to the standards for new work, and the openings in the new dwelling kept within 25% of its floor area. Where a building contains more than one dwelling, a SAP calculation can be used instead, to show the converted building's primary energy use and total emissions are no worse than if each dwelling had been improved element by element.
Most avoidable fails come down to unassessed thermal bridging left on SAP's conservative default psi values, which alone can push a sound design over its primary energy, emission and fabric energy efficiency targets. Others: a glazing specification the fabric can't carry, or a heating and ventilation spec that undershoots the target. Caught at design stage, all three are a specification change. Caught after work starts, they're a site problem. Revisions are included until the design meets its targets.
Its Approved Documents were published 24 March 2026. The regulations come into force 24 March 2027, with a 12-month transitional period to 24 March 2028. A building control application submitted before 24 March 2027, with work commenced before 24 March 2028, can still be built to Part L 2021.
The government has confirmed two methods for demonstrating FHS compliance during a phased transition. SAP 10.3 is an updated SAP 10.2, with a revised notional dwelling and carbon factors, available as the interim route. The Home Energy Model (HEM) is the longer-term replacement the industry is moving to. We work in SAP 10.3 now.