Energy statement baselines: Part L against policy targets

An energy statement baseline part L question usually arrives as a complaint from a case officer: the submitted statement shows Building Regulations compliance, and the local plan asks for a percentage improvement, and the two numbers in the report do not relate to each other. They are not meant to. One is a pass or fail against a notional building generated from your own geometry. The other is a reduction measured from a stated starting point. An energy statement has to carry both, clearly separated, with the arithmetic shown.

The confusion has a cause. Many adopted local plan policies were written against Part L 2013 and have not been updated since Part L 2021 took effect, so a policy asking for a 19 per cent improvement over the Building Regulations means something quite different today from what it meant when the policy was drafted.

What Part L compliance actually measures

Part L sets the target by reference to a notional building of the same size and shape as the one you are proposing, fitted with specified fabric and services. For dwellings the calculation produces three comparisons: emissions, primary energy and fabric energy efficiency, each of which the actual design has to better or match.

Two consequences follow, and both matter for planning.

First, the notional building moves with your design. A heavily glazed block gets a notional baseline with that same glazing, so its target is easier than a compact well-proportioned building's target. A Part L percentage improvement is therefore not comparable between two schemes, and quoting one as evidence of environmental performance is close to meaningless. The relationship between glazed area and the policy position is set out in heat loss from glazing ratio and design policy.

Second, Part L 2021 already delivered a substantial uplift against the 2013 edition, stated by government as around a 31 per cent reduction in carbon emissions for new homes and around 27 per cent for non-domestic buildings. A policy asking for 19 per cent over Part L 2013 is already satisfied by Building Regulations compliance alone.

What a policy improvement target measures

Planning policy targets measure a reduction from a declared baseline through a sequence of design moves. In London, Policy SI 2 of the London Plan requires major development to be net zero-carbon, with a minimum on-site reduction beyond the Building Regulations baseline and minimum proportions of that reduction to come from energy efficiency rather than from renewables, and a cash in lieu contribution to the borough's carbon offset fund for the residual.

The sequence is the energy hierarchy: be lean, be clean, be green, be seen. Each stage produces a number, and the policy target applies to the cumulative result.

The be green stage is where roof area becomes the binding constraint, competing with plant, amenity and greening, and the arithmetic of that competition is covered in roof area arithmetic.

Regulated against unregulated emissions

This distinction decides what goes in the table and what the offset payment is calculated on.

Regulated emissions are those arising from the building's fixed services: space heating, hot water, fixed cooling, ventilation, fixed internal lighting and auxiliary energy such as pumps and fans. Part L deals with regulated emissions and nothing else.

Unregulated emissions come from cooking, appliances, small power, external lighting and, in many cases, lifts. They are often the larger share of a modern well-insulated dwelling's actual energy use, which is an uncomfortable fact for any policy expressed purely in regulated terms.

State explicitly which set your percentages refer to. Where a policy is silent, assume regulated emissions and say so. Where a scheme is reporting unregulated figures voluntarily, keep them in a separate column rather than blending them, because a blended percentage cannot be compared with anything.

Carbon factors and why the answer changed

The carbon intensity figures inside the calculation methodology shifted substantially with the current version of the standard assessment procedure, with the electricity factor falling from the order of 0.519 kilograms of CO2 per kilowatt hour in the previous version to around 0.136 in the current one.

That single change rewrote the design logic. Electrified heating with a heat pump now scores well on carbon where it struggled before. Gas-fired combined heat and power, which used to be the standard route to a policy percentage on a large residential scheme, no longer produces a carbon saving against an all-electric alternative. Any energy statement reusing a strategy from a 2018 scheme is likely to be arguing for the wrong system.

State the methodology version and the carbon factors used at the front of the statement. Officers comparing your statement with one submitted two years ago need to know why the numbers look different.

Reporting both without confusion

Structure the Energy Statement so that the two assessments never share a table.

1. The regulatory section: Part L edition, calculation tool and version, the three target comparisons for dwellings or the equivalent for non-domestic, and a plain statement that compliance is achieved.
2. The policy section: the declared baseline, the four hierarchy stages with tonnes and cumulative percentage at each, the final on-site reduction, the residual emissions, and the offset calculation with the price per tonne and the period used.
3. A reconciliation paragraph explaining in words why the regulatory percentage and the policy percentage differ.

That third item is the one nobody writes and every officer wants. Three sentences are enough.

Keep the metering strategy consistent with whatever heat network or communal system the be clean stage relies on, because a policy saving claimed from a network that cannot be metered will not survive the discharge of conditions stage. The practical arrangements are covered in metering and submetering strategies for mixed use.

Where the two produce different answers

Four situations come up repeatedly.

A scheme passes Part L comfortably and misses the policy target, because Part L compliance can be achieved through services efficiency while a policy with a minimum energy efficiency component demands fabric improvements the designer skipped.

A scheme meets the policy percentage and fails Part L on fabric energy efficiency, because photovoltaics improve the emissions comparison without touching the fabric metric.

A mixed-use scheme produces different percentages for the residential and non-residential parts and an officer asks for a single figure. There is not one. Report each element separately and give a weighted total only with the weighting basis stated.

And a scheme with an unusual form gets a flattering Part L result and an unflattering policy result, or the reverse, for the reasons set out above. Say which is happening rather than leaving the officer to work it out.

Presenting the comparison to an officer

Lead with a half-page summary table showing both results side by side, with a one-line statement of what each measures. Then the detail.

Three things to include that applicants routinely leave out. The declared baseline in absolute tonnes per year, so the percentages can be checked. The offset contribution calculation in full, including the price per tonne applied and the number of years, since that figure goes into a section 106 obligation and will be queried. And the assumptions behind the renewable yield, including the panel area, orientation, tilt and the shading losses applied, because an unshaded yield on an overshadowed roof is the single most common challenge to a be green figure.

Where the authority also asks for embodied carbon, keep it entirely separate. A Whole Life Carbon Assessment covers different life cycle modules on a different methodology, and merging operational and embodied figures into one headline makes both unusable.

One honest caveat on timing. The Future Homes Standard has been consulted on and its start date and transitional provisions should be verified against the current published position before an energy strategy is fixed, because a scheme being designed now may be built under a different regulatory baseline from the one the planning statement assumed.

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This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.