Energy Statement or Sustainability Statement: which is which

An Energy Statement proves a number. A Sustainability Statement proves a policy position. That is the shortest honest answer to the energy statement vs sustainability statement question, and it explains why a council can ask for both on the same application without duplicating anything.

The Energy Statement is a calculation document. It shows the regulated carbon emissions of the proposed building, the reduction achieved against the Building Regulations baseline, and how that reduction was produced stage by stage. The Sustainability Statement is a policy compliance document. It walks through the adopted local plan policies on sustainable design and answers each one with evidence, of which the energy calculation is only a part.

Confusing the two produces the document architects most often get bounced on: a forty-page sustainability statement with no target emission rate in it, or an energy statement that says nothing about water, materials or climate resilience.

What each document is asked to prove

The Energy Statement answers a quantitative question. What are the regulated emissions of this building, what would they have been under a notional building compliant with Part L, and what is the percentage improvement?

The Sustainability Statement answers a list of qualitative and quantitative questions drawn from the development plan. Does the scheme meet the water efficiency standard the local plan requires? What is the materials strategy? How does the design respond to a warming climate? Is there a construction waste target? Has biodiversity been addressed? Some answers are numbers, some are commitments, and several will cross-refer to other documents in the pack.

A useful way to keep them apart: if the answer comes out of a software model, it belongs in the Energy Statement. If it comes out of reading a policy and explaining how the scheme responds, it belongs in the Sustainability Statement.

Regulated energy and the hierarchy

Regulated energy is the energy the Building Regulations control: space heating, hot water, fixed lighting, ventilation and cooling. Unregulated energy, meaning appliances and plug loads, sits outside Part L and outside most energy statement targets, though some policies now ask for it to be reported separately.

The energy hierarchy structures the reduction. Demand reduction first, then efficient supply, then renewable generation, then, in London and a growing number of authorities, monitoring of actual performance after occupation. Each stage is reported with its own emissions figure so the reader can see what produced the saving. The stage-by-stage treatment is set out in more detail in the energy hierarchy explained.

Two practical points. Fabric measures have to be modelled as built, not as aspiration, because the same fabric specification goes into the Building Regulations submission later and a gap between the two is an obvious target at discharge of conditions. And roof area is finite: a scheme that needs a large photovoltaic array to hit its target should show the array on a roof plan alongside the plant, the terraces and the green roof competing for the same square metres.

Where the wider sustainability topics belong

Everything that is not regulated energy goes in the Sustainability Statement, and the list is longer than most architects expect at the start of a job.

• Water efficiency, usually expressed in litres per person per day and secured by condition.
• Materials, including responsible sourcing and any policy target on recycled content.
• Construction and operational waste, including provision for separated storage.
• Climate resilience: overheating, drainage, urban greening.
• Biodiversity, cross-referring to the ecology work rather than repeating it.
• Sustainable transport, cross-referring to the transport documents.
• Any adopted certification requirement such as a BREEAM rating for non-domestic floorspace.

Do not answer a policy by quoting it back. The failure mode here is a table with the policy text in the left column and the words "the scheme complies" in the right. Say what the scheme does, give the number, and name the drawing or report where it is shown.

The modelling outputs behind each

An Energy Statement for dwellings is built on SAP outputs. For non-domestic floorspace it is built on SBEM or an approved dynamic simulation model. The statement should include the actual output sheets as an appendix rather than a summary table alone, because the reviewer's first job is to check that the model matches the drawings.

The baseline matters more than the percentage. A reduction quoted against an old edition of Part L is not comparable with one quoted against the current edition, and reviewers will ask which notional building you used. State the edition in the first paragraph of the statement and again in the summary table.

Overlap with carbon and overheating work

Three documents draw on the same design information and contradict each other more often than they should.

Overheating is the clearest example. The Energy Statement improves the fabric and may add solar gain through larger glazing to help daylight. The Overheating Risk Assessment then tests the same rooms under CIBSE TM59 and fails them. If the mitigation is external shading or restricted glazing, the energy model has to be rerun. Doing the overheating work last guarantees rework.

Whole life carbon covers embodied emissions across the life cycle modules, which the Energy Statement ignores entirely. The two documents share a specification and a floor area schedule, and those are worth fixing once and circulating, because a mismatch between the gross internal area in one and the other is the first thing a reviewer notices.

Where a BREEAM pre-assessment is required, its energy credits depend on the same model. Run them from the same file.

Local plan policies that ask for both

Most English authorities now carry a sustainable design and construction policy and a separate energy or carbon policy. The two documents map onto that split, which is why councils ask for both.

Check the validation list rather than guessing. Some authorities fold both into a single "sustainability and energy statement" and will reject two separate documents as duplication. Others specify a proforma. In London, the energy assessment requirements for referable and major schemes are set by the London Plan and the Greater London Authority's guidance, and the reporting format is prescribed closely enough that a free-form statement will be sent back.

Where a policy predates the current Part L edition, say so and explain how you have translated the target. That is a legitimate planning argument and officers deal with it regularly. Silence on the point is what causes the query.

Keeping one set of numbers across the pack

The single most useful thing an architect can do on a scheme with several sustainability documents is to maintain one schedule of agreed figures and circulate it to every consultant.

Put the gross internal area, the unit mix, the fabric U-values, the heating system, the photovoltaic area and capacity, and the modelled emissions at each hierarchy stage in one table with a version number. Every report quotes from that table. When the design changes, the table changes and everyone is told.

It sounds like housekeeping. It is the difference between a discharge of conditions that takes a fortnight and one that takes four months, because a sustainability officer who finds two different roof areas in the same submission will stop reading and write to ask which is right.

One honest uncertainty: the Future Homes Standard will change the baseline that energy statements are written against, and until it is in force there is a period where local policy targets and the Building Regulations baseline sit awkwardly together. Say in the statement which baseline you used and on what date, so the document can be read correctly later.

Browse the PlanScope report types to see how the energy, sustainability and carbon documents fit together for a given scheme.

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