Competence for a sustainability statement
A sustainability statement is policy compliance work, not modelling. Here is who writes it, which figures have to be imported and which commitments are enforceable.
A sustainability statement is a policy compliance document, and the person best placed to write it is whoever holds the adopted local plan policies and the design information: usually the architect or architectural technologist on a small scheme. It does not need a licensed assessor. What it does need is someone willing to go through the authority's sustainable design policy line by line and say what the scheme does about each requirement, with the numbers imported from whoever calculated them.
The confusion with an energy statement causes most of the trouble. One is a policy checklist across many themes. The other is a modelled carbon reduction exercise, and the people who can produce it are a narrower group.
What the statement is asked to demonstrate
A Sustainability Statement answers the question a case officer has to answer at the end of the assessment: does this scheme comply with the authority's sustainable design and construction policies, and where it does not, why.
The themes recur across most local plans. Energy and carbon, water efficiency, overheating, materials, construction and operational waste, biodiversity, drainage, transport and travel, air quality, and climate resilience. Some authorities add food growing, green roofs or an urban greening target.
The structure that works is the policy itself as the spine. Quote the policy requirement, state what the scheme provides, give the number or the drawing reference, and say where the supporting evidence sits. An officer can then verify compliance without reading the whole document, which is the point.
Where the statement has to cover themes with their own technical reports, it should summarise and cross-reference rather than reproduce. Duplicating the drainage calculation in the sustainability statement creates an opportunity for the two documents to disagree.
Policy checklist work compared with modelling
The division of competence is cleaner than people assume.
Checklist work needs planning literacy. Reading the adopted plan correctly, identifying which policies apply to this scale of development, distinguishing a requirement from an aspiration, and recognising where a supplementary planning document adds detail. An architect, a planning consultant or a competent technologist can do this.
Modelled work needs accreditation or specialist software. SAP calculations for dwellings need an accredited domestic energy assessor. Non-domestic carbon figures need SBEM modelling. Overheating assessment to the CIBSE methodology needs dynamic simulation and the judgement to select rooms and weather files. BREEAM ratings need a licensed assessor.
So a sustainability statement on a self-build or small scheme is usually written by the design team and populated with figures produced by others. Name the source of every number and the person who produced it. The reasons for doing that consistently across a submission are set out in why a planning report needs a named author and date.
Water efficiency calculations and their basis
Water efficiency is the one calculation a competent non-specialist can usually do themselves, and it is the one most often got wrong.
The method comes from Part G of the Building Regulations, which sets a fittings-based calculation using the government water efficiency calculator for new dwellings. The baseline requirement is 125 litres per person per day. An optional tighter requirement of 110 litres per person per day exists, and it can only be applied where the local plan contains a policy justified by evidence of local water stress, as the guidance on optional technical standards explains.
The calculation itself is arithmetic on fittings: WC flush volumes, basin and sink tap flow rates, shower flow rate, bath capacity, and the presence of a dishwasher and washing machine, each with a fixed use factor. A rainwater or greywater system earns a deduction.
Two errors recur. The first is quoting the 110 figure where no policy imposes it, which commits the applicant to a specification nobody asked for. The second is submitting a fittings schedule that the eventual bathroom specification will not match, because the figure was calculated on a 6 litre per minute shower and the client wants a rain head. Build in margin.
| Element | Who is competent | Output used in the statement |
|---|---|---|
| Policy compliance narrative | Architect, technologist, planner | Policy-by-policy response |
| Water efficiency | Designer using the Part G calculator | Litres per person per day with fittings schedule |
| Dwelling carbon figures | Accredited domestic energy assessor | Percentage improvement over the target rate |
| Non-domestic carbon | Specialist modeller | Modelled emission rate comparison |
| Overheating | Dynamic simulation specialist | Pass or fail against the chosen criteria |
| BREEAM | Licensed assessor | Pre-assessment score and target rating |
Where energy modelling has to be imported
If the authority's policy sets a percentage carbon reduction over the Building Regulations target, the sustainability statement cannot answer it without modelled output. That number comes from the Energy Statement and the assessor who produced it.
The cross-reference needs to be exact. State the regulation edition the modelling was run against, the target emission rate, the dwelling or building emission rate achieved, and the resulting percentage. A statement claiming a percentage improvement without naming the baseline is not verifiable, and officers now ask.
Overheating is the other imported element. Where the authority expects an assessment against the CIBSE methodology, the figures come from a dynamic model and belong in an Overheating Risk Assessment with the statement summarising the conclusion. Do not assert compliance with the Building Regulations overheating requirement on the basis of opening windows, because on a single-aspect flat beside a busy road that argument fails.
Materials and waste commitments
Materials sections are where sustainability statements become vague, and vagueness is what officers condition.
Commitments that can be written and kept include responsibly sourced timber with a named certification scheme, a stated percentage of recycled or secondary aggregate, locally sourced facing materials with the source identified, a site waste target with a diversion from landfill percentage, and reused material from demolition quantified by the pre-redevelopment audit.
Commitments that cannot be kept, and should not be made, include unquantified promises to minimise embodied carbon, references to materials with low environmental impact without a standard attached, and any claim that depends on a supplier who has not been approached. Where embodied carbon is a policy requirement, that is a whole life carbon exercise with its own methodology and should be dealt with as such rather than asserted in a paragraph.
Avoiding unenforceable promises
A planning officer reads a sustainability statement looking for things to condition. Anything specific and measurable becomes a condition that has to be discharged. Anything vague becomes a condition requiring further details, which costs the applicant more.
Write commitments as a specification, with a number, a unit and a stage at which it will be evidenced. And be careful about committing to a standard the scheme cannot certify, because a condition requiring a final BREEAM certificate at a stated rating is enforceable and a scheme that misses it by one credit is in breach.
The honest position on small schemes is that some policy requirements were written with larger developments in mind and sit awkwardly on a single dwelling. Say so, with reasons, rather than claiming compliance that the scheme cannot deliver. Officers respond better to a reasoned explanation of partial compliance than to a statement that collapses at discharge of conditions stage.
Who in a design team usually owns it
On a self-build or a scheme of a few units, the architect owns the document and the energy assessor supplies the carbon figures. On a scheme of 20 units upwards, a sustainability consultant usually takes it, because the number of imported calculations grows and someone has to hold the interfaces.
Whoever owns it needs three things: access to the adopted local plan and any relevant supplementary guidance, the design information at the right level of detail, and authority to say no to a commitment the project cannot deliver. That third point is the one that gets skipped.
If you want the draft checked by someone with the right accreditation before it goes in, the professional directory lists reviewers who can sign off a report in the relevant discipline.
PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. For specialist technical reports, qualified professional input may be required.
Frequently asked questions
Does a sustainability statement need an accredited author?
No. It is a policy compliance document and can be written by an architect, technologist or planning consultant with access to the adopted local plan. The figures inside it often do need accredited authors, including SAP calculations by a domestic energy assessor and BREEAM scores by a licensed assessor, so name the source of each number.
How is the water efficiency figure calculated?
Using the fittings-based method in Part G of the Building Regulations and the government water efficiency calculator for new dwellings. You enter WC flush volumes, tap and shower flow rates, bath capacity and whitegoods, each with a fixed use factor. Rainwater or greywater reuse earns a deduction from the total.
When does the 110 litre standard apply?
Only where the local plan contains a policy applying the tighter optional requirement, justified by evidence of local water stress. The default requirement is 125 litres per person per day. Quoting 110 litres where no policy imposes it commits the applicant to a specification the authority never asked for.
How does it differ from an energy statement?
An energy statement is a modelled carbon exercise producing a percentage improvement over the Building Regulations target rate. A sustainability statement covers many themes, including water, materials, waste, overheating, biodiversity and transport, and imports the carbon figures by cross-reference rather than producing them.
What makes a sustainability commitment enforceable?
A number, a unit and a stage at which it will be evidenced. Responsibly sourced timber under a named certification scheme is enforceable. A promise to minimise embodied carbon is not, and officers typically respond by imposing a condition requiring further details, which costs the applicant more than writing the specification properly.
Sources and further reading
This article is general guidance about the planning system in England and, where stated, the rest of the UK. It is not legal or professional advice. Check your local planning authority’s validation requirements and take professional advice for your specific site.