SAP outputs an energy statement has to show

An energy statement that quotes a percentage improvement without showing the calculation behind it gets sent back. What an officer needs from the SAP outputs is the comparison against the notional building, expressed in the three metrics Part L 2021 uses, with the same dwelling mix as the drawings and the same assumptions as the rest of the application.

Part L 2021, which applies through Approved Document L Volume 1 for new dwellings, moved the primary compliance metric to primary energy while keeping carbon and fabric targets alongside it. That means three pass or fail tests per dwelling rather than one, and a planning energy statement that reports only carbon is incomplete before anyone starts reading it.

Why the notional building is the benchmark

Part L does not set an absolute energy or carbon figure for a dwelling. It creates a notional building of the same size, shape and orientation as the one being assessed, applies a defined specification to it, runs the same calculation, and uses the result as the target. Compliance means the actual dwelling performs at least as well as its own notional twin.

The consequence for design is not obvious until you have run a few. Because the notional building shares the geometry of the real one, a poorly shaped dwelling with a high heat loss form factor gets a correspondingly easier target, and a compact block gets a harder one. Two dwellings with the same percentage improvement over target can have very different energy demands in kWh per square metre per year. Where a local plan sets an absolute energy use intensity target alongside the percentage, both have to be reported.

Regulated against unregulated emissions

Regulated emissions are those from the fixed building services covered by the calculation: space heating, hot water, ventilation, pumps, fans and fixed lighting. Unregulated emissions come from everything else the occupant plugs in, including cooking, appliances and small power.

Building Regulations compliance deals only with regulated emissions. Several planning policies, the London Plan among them, ask for both to be reported, and some carbon offset calculations are based on the regulated figure alone. Be explicit about which basis each number uses. The most common inconsistency in submitted statements is a carbon saving expressed against regulated emissions in one table and total emissions in another, with no note explaining the change.

The outputs an officer expects to see tabulated

Present the results as a table, per dwelling type and then aggregated for the scheme, rather than as prose. The figures that belong in it:

Attach the SAP worksheets or the BRE output documents as an appendix. An officer or their consultant will check that the areas in the SAP match the accommodation schedule, that the number of dwellings matches the application, and that the specification in the tables matches the one in the energy statement narrative. Those three checks catch most errors.

Carbon factors and why the electricity figure moved

SAP 10 revised the carbon emission factors used in the calculation, and the change to grid electricity was the one that altered design decisions across the industry. The factor fell to 0.136 kg CO2 per kWh, against a gas factor of around 0.210, reflecting the decarbonisation of electricity generation.

That reversal is why heat pumps now produce better carbon results than gas boilers in the calculation, and why direct electric heating is no longer automatically penalised in carbon terms even though it performs badly on primary energy and on running costs. Say which version of SAP was used, because a statement produced on SAP 2012 factors and one produced on SAP 10.2 are not comparable, and older documents still circulate.

The fuel factor treatment also matters where the scheme is not connected to gas. Set out the assumption rather than leaving the reader to infer it from the results.

Presenting the improvement over the target rate

Percentage improvement is the number that policy usually turns on, and it is the number most often presented in a way that cannot be checked.

State the baseline explicitly: improvement over the Part L 2021 notional building, not over an earlier edition. Where the London Plan applies, the Greater London Authority's energy assessment guidance sets out how the improvement is to be calculated and reported at each stage of the Be Lean, Be Clean, Be Green, Be Seen hierarchy, with savings attributed to each stage separately rather than as a single figure. Check the current version of that guidance, since the percentages and the reporting format have been revised as the Building Regulations baseline changed.

Show the savings stage by stage: the reduction from fabric and passive design, then from efficient supply, then from renewables. A scheme claiming a large improvement delivered entirely by photovoltaic panels on a roof that also carries plant will be asked to prove the panels fit.

Where design stage figures diverge from as built

The SAP submitted with a planning application is a design stage calculation. The as-built calculation is produced after completion, using the specification actually installed and the measured air permeability from testing.

Divergence is normal and usually small. It becomes a planning problem where a condition requires the development to achieve the reported performance, because the as-built figure is what will be tested against it. Three things cause most of the gap: substitution of specified products during procurement, thermal bridging assumptions replaced by default values when the accredited details are not achieved, and air permeability results worse than the design assumption.

Where a condition requires evidence of compliance post-completion, keep the design stage assumptions conservative. A statement that assumes a perfect air permeability result to reach a target leaves no margin, and the discharge of that condition becomes a problem for someone two years later.

Keeping the statement consistent with the drawings

The failure mode that wastes most time is internal inconsistency. The assessor works from one set of drawings, the architect revises them, and nobody re-runs the calculation.

Check before submission that:

• Dwelling count, unit mix and floor areas match the accommodation schedule.
• Glazing areas and orientations in the SAP match the elevations.
• Plant shown in the energy strategy has space on the drawings, including flue routes, cylinder cupboards and external unit positions for heat pumps.
• The photovoltaic array area fits on the roof plan alongside rooflights and plant.
• The ventilation strategy matches the one assumed in any overheating risk assessment prepared under Approved Document O.

The overheating point deserves attention. A fabric-first strategy with large south-facing glazing can pass Part L and fail Part O, and resolving that after planning permission usually means changing the elevations. Run both together. Where a wider sustainability statement is also required, the water efficiency and carbon figures in it should be drawn from the same model rather than assembled separately.

And if the scheme changes materially after submission, re-run the calculation and issue an addendum. Officers notice when the drawing revision date is later than the energy statement, and the question that follows is rarely a quick one. For the assumptions officers query most often, see the energy modelling assumptions that tend to attract scrutiny.

PlanScope drafts energy statements structured to UK planning policy, with the SAP outputs and site-specific figures flagged for your assessor to supply. Browse the report types and start a draft. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval, and SAP calculations must be produced by an accredited energy assessor.