Do you need an energy statement for an extension? For most householder extensions in the UK, the honest answer is no — but check your council first. There is no national planning rule requiring one, yet a growing number of local authorities ask for energy or sustainability information with householder applications through their validation checklists, and building regulations Part L applies to every extension regardless of what planning asks for.
This guide explains when an extension does need an energy statement, how to check your own council's position in five minutes, and what a proportionate extension energy statement should contain if you are asked for one.
When does an extension need an energy statement?
An energy statement is normally associated with new-build development: councils use it to check a scheme's carbon reduction strategy against local policy. For extensions, requirements split three ways:
- Most councils: not required. Householder validation lists in the majority of authorities do not mention energy statements, and the application is judged on design, amenity and other standard matters.
- Some councils: required or encouraged for householder schemes. A minority of authorities — Stockport is a well-known example, with its published energy efficiency statement requirement — ask householder applicants to describe the energy efficiency measures considered. These are usually short, proportionate documents, not full SAP-modelled statements.
- Larger projects and special cases: often required. If the "extension" is really a major refurbishment, creates a new dwelling or self-contained annexe, or forms part of a larger scheme, energy policies for new development can be engaged — and in London, borough-level requirements reach smaller schemes than elsewhere.
The deciding document is always the council's local list of validation requirements, so that is the first thing to check.
How do you check your council's requirements?
Three steps, five minutes:
- Search "[your council] local list validation requirements" and open the householder column. Look for entries such as "energy statement", "energy efficiency statement" or "sustainability checklist".
- Check whether the local plan has a climate change policy that applies to all development — some councils hook householder requirements off such policies even when the validation list is silent.
- If it is still unclear, ask the duty planner or use pre-application advice. A one-line email now is cheaper than an invalid application later.
Planning vs building regulations: Part L applies either way
Whatever planning asks for, every extension must comply with Approved Document L of the building regulations. For extensions to existing homes, Part L 2021 sets limiting U-values for new walls, floors, roofs and windows, and rules on the area of glazing. This is checked at building control stage, not planning — a point that confuses many applicants. An energy statement is a planning document about strategy and policy compliance; Part L compliance is demonstrated separately, whether or not a statement was ever required. (An EPC is different again — see EPC vs energy statement.)
It is also worth knowing what is coming: the Future Homes Standard, published in March 2026, takes effect for new dwellings from March 2027. It does not rewrite the extension rules, but it signals the direction — councils are increasingly interested in energy performance at every scale.
What goes into an extension energy statement?
Where a council does ask for one, keep it proportionate. A good extension energy statement typically covers:
- Fabric performance — the U-values you will achieve for new elements, ideally better than the Part L limiting values, plus airtightness and thermal bridging intentions;
- The energy hierarchy in miniature — following the same Be Lean, Be Clean, Be Green logic used for major schemes: reduce demand first, then supply heat efficiently, then add renewables;
- Heating strategy — how the extension will be heated, and whether the project is a sensible trigger to upgrade the whole house (for example to a heat pump, which has its own permitted development rules);
- Renewables where practical — typically roof-mounted solar PV on suitable orientations;
- Measures considered but rejected, with brief reasons — councils asking for these statements usually want evidence that options were weighed, not a promise of perfection.
How much does an extension energy statement cost?
Because no SAP modelling of a full dwelling is normally needed, an extension-level statement sits at the bottom of the price range — often a few hundred pounds from a consultant, and less where the information can be assembled from your architect's specification. Our guide to energy statement costs in the UK sets out indicative figures for every scheme size.
Key takeaways
- There is no national requirement for an energy statement with a householder extension application — but individual councils can and do ask for one via their validation lists.
- Check your council's local list before submitting; an invalid application is the most common own goal.
- Part L of the building regulations applies to every extension regardless of planning requirements — U-values and glazing limits are checked at building control stage.
- Where a statement is required, keep it proportionate: fabric first, an efficient heating strategy, and renewables where they make sense.
How Fortress Associates can help
If your council does ask for an energy statement — for an extension, a new dwelling or a larger scheme — Fortress Associates' automated energy statement service produces a free report in minutes for any UK local authority, built on a Part L 2021 / SAP 10.2 baseline and working through the full Be Lean, Be Clean, Be Green energy hierarchy with CO₂ savings calculated at each stage. Contact us if you are not sure what your council needs, or browse our other planning report services.
Sources & further reading
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