Showing be lean savings separately in an energy statement

An energy statement that reports a single combined carbon saving will come back. The energy hierarchy of be lean, be clean and be green is a sequence, and the point of the sequence is that each stage has to earn its own reduction. A scheme that reaches 38 per cent overall with almost all of it coming from photovoltaic panels has not demonstrated compliance with a policy that expects demand to be cut first, however good the headline looks.

Why the stages are reported separately

The hierarchy exists because the measures are not interchangeable. Fabric performance lasts the life of the building and needs no maintenance contract. A heat network connection depends on a third party. Panels degrade, get shaded by later development and can be removed.

So policy puts a floor under the first stage. London Plan 2021 policy SI 2 and the Greater London Authority's energy assessment guidance set a minimum on-site reduction against the Building Regulations baseline, with a sub-target that has to be achieved through energy efficiency alone, set higher for non-residential than for residential schemes. Confirm the current figures and the baseline before you draft, because both have moved with each Part L uplift.

Outside London the wording varies, and many local plans simply require a percentage reduction without separating the stages. Report them separately anyway. Officers outside London increasingly use the same structure, and a statement that cannot show its demand reduction separately is hard to condition and harder to defend at appeal.

Demand reduction and the fabric measures

Stage one is everything that reduces the energy the building needs before any plant is specified. Orientation, form factor, glazing ratio and distribution, air tightness, thermal bridging, insulation thickness, ventilation strategy and lighting efficiency.

Report it as the change in regulated carbon emissions between the baseline model and a model with the improved fabric and no low-carbon supply. That is the figure the sub-target is measured against. Two things commonly get smuggled in at this stage and should not be: heat pumps, which belong in stage three, and photovoltaic panels, which also belong in stage three.

Form factor does more work here than any single U-value, which is why a terrace outperforms a detached house on identical specifications. Where the fabric specification is being set, the U-values officers look at are a useful starting point, though the figures that matter are the ones in your own model rather than a table.

Air tightness is the measure most likely to be challenged, because it is the one that depends on site workmanship rather than specification. If your stage one saving relies on a figure materially better than the Building Regulations requirement, expect a condition requiring post-completion testing.

Efficient supply

Stage two covers how energy is delivered rather than how much is needed. Connection to an existing or planned district heat network, communal heating where it is justified, and combined heat and power where it still makes sense, which is increasingly rare as the grid decarbonises.

The honest position on many schemes is that stage two delivers nothing. There is no network within reach, communal heating adds distribution losses, and gas-fired combined heat and power no longer produces a carbon saving against grid electricity. Say that, with the reason, and show a zero.

Where there is a network in the area, the usual expectations are a connection where one is available, a connection point and plant space safeguarded where the network is planned, and evidence of the enquiry you made to the operator. A statement claiming a future connection with no correspondence behind it carries no weight.

Renewables and the third stage

Stage three is on-site renewable generation. Photovoltaic panels on roofs, air source and ground source heat pumps, and solar thermal where hot water demand supports it.

Two practical constraints shape the answer. Roof area competes with plant, terraces, green roofs and rooflights, so the panel area in the energy statement has to match the roof layout drawing rather than the gross roof footprint. And the grid connection capacity may limit export, which does not affect the carbon calculation directly but does affect whether the array makes commercial sense, particularly where battery storage alongside the array is being considered to manage it.

Heat pumps sit here and they interact with stage one. A heat pump sized for a poor fabric specification needs more plant space, draws more electricity and produces more noise, so the stages move together even though they are reported apart.

The cumulative table officers expect

The table below is the structure most reviewers work from. Report regulated emissions in tonnes of carbon dioxide per year, the saving at each stage, and the cumulative percentage against the baseline.

Give the residual emissions as well, because that is what any carbon offset payment is calculated on, usually over a 30-year period at the price in the authority's own published guidance. Include the modelling software and version, the weather file and the compliance calculation used, so the figures can be reproduced.

Where the scheme is in outline or where whole life carbon is also required, keep the operational figures in the energy statement and the embodied figures in the Whole Life Carbon Assessment. Mixing them produces a number nobody can check.

Mistakes that collapse the stages together

The recurring errors are worth listing because they are easy to avoid and expensive to correct.

• Running one model with every measure in it and apportioning the saving afterwards. The stages have to come from separate model runs.
• Counting photovoltaic output or heat pump efficiency inside the demand reduction figure.
• Reporting unregulated energy alongside regulated energy without labelling which is which.
• Using a baseline from the wrong Part L edition, or comparing a notional building against a different notional building. If the baseline is unclear, the explanation of the notional building will save a round of comments.
• Changing the dwelling mix after the model was run and not rerunning it.
• Showing a percentage with no absolute figures, so the saving cannot be checked against the floor area.

An illustrative example. A 60-unit block reports a baseline of 100 tonnes of regulated carbon dioxide a year. Fabric measures take it to 88, a 12 per cent cut. There is no heat network, so be clean shows no change. An air source heat pump system and a rooftop array take it to 61, giving a cumulative 39 per cent. The statement reports all three stages, the residual 61 tonnes and the offset calculation. Figures here are illustrative.

Conditions and what gets checked later

Expect conditions attached to each stage rather than to the total. Typical wording requires the approved fabric specification to be built, requires evidence of the air tightness test result before occupation, safeguards the heat network connection point, and requires the renewable installation to be in place and retained.

That matters commercially. A total that can be met several ways gives you flexibility. A set of stage conditions does not, and swapping fabric performance for extra panels after permission needs a non-material amendment at best and a section 73 application at worst. Agree the conditions wording when the officer drafts them, not after.

The one honest uncertainty here is the offset price. It is set locally, reviewed periodically, and can change between your appraisal and your decision, so treat the figure in the authority's current guidance as a snapshot. Draft your Energy Statement so the residual emissions figure is easy to find, because that is the number the offset calculation attaches to.

This is general guidance, not legal advice. Check the current policy wording and guidance applying to your site, and take advice from 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.