The be lean chapter of an energy statement
The first stage of the energy hierarchy reports the saving achieved by fabric, form and services efficiency alone. Here is what belongs in it, in what order, and what does not.
The be lean energy statement chapter is the one an officer reads to find out whether the building needs less energy, or whether the applicant has simply bolted a heat pump onto an ordinary design. It is the first stage of the energy hierarchy, it deals with demand reduction alone, and the saving it reports has to be achieved by the building fabric, the form and the services efficiency before any low carbon supply is counted.
Written properly it is two pages and a table. Written badly it is eight pages of measures with no numbers attached.
What the chapter has to show
One quantity matters: the reduction in regulated energy demand and the associated carbon saving achieved by demand reduction measures alone, expressed against the stated baseline.
That means three model runs reported in sequence. The compliance baseline generated from the notional building under the current edition of the Building Regulations. The building with the demand reduction measures applied. And, separately in later chapters, the effect of efficient supply and of renewable generation.
Report absolute figures alongside percentages. Kilograms of carbon dioxide per square metre per year and kilowatt hours per square metre per year survive a change of baseline edition. Percentages do not.
Greater London Authority guidance sets minimum expectations for the saving achieved at this stage alone, and the expectations differ between residential and non-residential development. Check the current version of that guidance before setting a target, because both the figures and the baseline they are measured against have been revised.
Fabric measures and the order they belong in
List them in the order of influence on the result rather than in the order the design team happened to resolve them.
- Form factor, the ratio of heat loss area to treated floor area, which is fixed by massing and is the single most powerful lever available.
- Opaque fabric U-values for walls, roof and ground floor.
- Glazing specification, covering U-value, g-value and the frame.
- Thermal bridging, reported as calculated linear transmittance values for the actual junction details rather than as default values.
- Air permeability, with the design target and the testing regime stated.
Thermal bridging is the measure most often reported as a default because the junction details have not been designed. That is an honest position at outline stage and a weak one at a detailed application, and an officer who has seen a few of these will spot it.
Form factor rarely appears at all, which is odd given that it is settled before anything else and cannot be improved later. A compact block with a form factor well below a detached house will outperform it on fabric with a less demanding specification, and saying so explains the design rather than defending it.
Glazing ratio and the tension nobody writes down
Increasing glazing raises heat loss, raises solar gain and raises daylight. Reducing it does the reverse. The chapter frequently reports a glazing reduction as a saving without mentioning what it cost elsewhere.
Be honest about the trade-off. A reduced glazing ratio that improves the energy result and worsens the daylight position for the units behind it is a design decision, not a free gain, and the daylight evidence will be read by the same officer.
The same applies to overheating. Measures that improve the carbon result, more insulation and tighter construction, push the overheating assessment the other way. Run the Overheating Risk Assessment alongside this chapter rather than afterwards, because a glazing change made to pass one test invalidates the other.
Ventilation and heat recovery
Ventilation sits in this chapter because the energy to condition incoming air is demand, and reducing it is demand reduction.
State the strategy, the system type, the specific fan power and the heat recovery efficiency, and state them as design values the installed system will have to meet rather than as manufacturer best case. A mechanical ventilation system with heat recovery claimed at a high efficiency and installed with poorly insulated ductwork in an unheated space does not deliver what the model assumed.
Where the strategy is natural ventilation, say how it works in the units that cannot open windows because of noise or air quality, since those are the ones that will drive the design. On a site next to a busy road the answer is usually mechanical, and the energy statement should admit that rather than modelling a window the acoustician has already closed.
Reporting the saving stage by stage
A single table carries the chapter.
| Stage | Regulated carbon | Regulated energy | Saving |
|---|---|---|---|
| Baseline from the notional building | State | State | n/a |
| After demand reduction | State | State | State |
Two rules keep it honest. Count each measure once, in the stage where it belongs, because an efficient heat pump is supply rather than demand and claiming it here inflates the first stage. And state the calculation methodology version alongside the figures, since the engine changes between editions.
Where the scheme is phased or has mixed uses, report by use and then in total. An aggregated figure across residential and commercial hides the stage at which one of them is underperforming, and authorities with separate targets for each will ask for the split anyway.
Where the chapter gets padded
Four patterns recur, and each one is visible to a reader who has looked at a hundred of these.
A list of measures with no quantified contribution attached. If a measure cannot be given a number, it belongs in the design narrative rather than in the energy statement.
Generic text about passive design principles that could apply to any building. Delete it. An officer reading 20 energy statements a month recognises the paragraph from the last one.
Claiming the same saving twice, usually by counting a low carbon heating system in both the demand reduction and the supply stages.
And a percentage with no baseline stated, which makes the whole chapter unverifiable. Our note on fabric first evidence in a planning submission covers what the quantified version looks like.
Linking the chapter to the compliance calculation
The energy statement is a planning document and the compliance calculation is a regulatory one, and the two have to agree.
Attach the calculation output for each stage, with the file references, so the officer can see that the figures in the table came from somewhere. A table of numbers with no output behind it is the commonest reason these chapters attract a request for further information. Where the application is outline or the design is early, say which assumptions are provisional and commit to the stage outputs at a later point, usually by condition.
Standards move, and a statement prepared under one edition of the regulations will be read against another if the application sits for a year. The route the Future Homes Standard takes will change the notional specification again, and our piece on designing now for the Future Homes Standard sets out what is worth doing in advance. State in the Energy Statement which rules it was prepared under and on what date.
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.
Frequently asked questions
What counts as a demand reduction measure?
Anything that reduces the energy the building needs before it is supplied: form factor, opaque fabric U-values, glazing specification, calculated thermal bridging, air permeability, efficient ventilation with heat recovery, and efficient lighting with controls. Low carbon heat supply and renewable generation belong in the later stages and should not be counted here.
Why does form factor matter so much?
Because it is the ratio of heat loss area to treated floor area, it is fixed by the massing before any specification is chosen, and it cannot be improved later. A compact block with a low form factor meets the same target with a less demanding fabric specification than a detached or highly articulated building of the same area.
Should thermal bridging use default values?
Only where the junction details genuinely do not exist, which is an honest position at outline stage and a weak one on a detailed application. Calculated linear transmittance values for the actual details give a better result and demonstrate that the construction has been thought through. Experienced officers notice defaults in a detailed submission.
How should the saving be reported?
As a table showing the compliance baseline from the notional building, then the figures after demand reduction, with absolute values in kilograms of carbon dioxide and kilowatt hours per square metre per year alongside the percentage. State the baseline edition and the calculation methodology version, because percentages alone cannot be compared across editions.
Does reducing glazing count as a saving?
It changes the energy result, but it is a trade-off rather than a free gain. Less glazing reduces heat loss and solar gain and also reduces daylight, and the daylight evidence will be read by the same officer. Say what the reduction cost elsewhere rather than reporting only the side that helps.
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.