Carbon and energy evidence on a section 73 variation
Vary a condition and the authority decides afresh what conditions the new permission should carry. That is why the energy statement gets reopened, and how to keep it proportionate.
A section 73 application produces a new planning permission, and that single fact is why your energy evidence gets reopened. You applied to change a condition about unit mix or a drawing number, and the officer comes back asking for an updated Energy Statement against current policy. That is not officiousness. Section 73 of the Town and Country Planning Act 1990 creates a fresh permission subject to its own conditions, and the authority decides what those conditions should be in the circumstances that exist now.
The practical skill is scoping the variation so the energy question stays proportionate, and knowing which route to use when it will not.
What a section 73 can and cannot do
Section 73 allows an application for planning permission to develop land without complying with conditions attached to a previous permission. The authority considers only the question of the conditions, and it grants a new permission if it decides the conditions should be varied or removed.
Two limits matter here.
The description of development cannot be changed. The Court of Appeal decision in Finney v Welsh Ministers settled that a section 73 cannot be used to vary a condition in a way that conflicts with the operative part of the permission, which means a variation that in substance changes what was permitted needs a different route.
Conditions imposed on the new permission must be ones the authority could lawfully have imposed on the original grant, and they must meet the six tests in Planning Practice Guidance. That is a real constraint, and it is the basis on which you push back when a request goes too far.
Section 73B of the 1990 Act, inserted by the Levelling-up and Regeneration Act 2023, provides a further route for development that is not substantially different from an existing permission. As at 13 October 2026, check its commencement position and any regulations on legislation.gov.uk before relying on it.
Why the energy evidence gets reopened
Because the new permission is granted today, the policies in force today are material to the conditions attached to it. Where the original permission carried an energy condition referencing an approved statement by date, the authority has to decide what the equivalent condition should say on the new permission.
Three triggers make a reopening more likely.
The variation changes the built form. More floorspace, a different envelope, altered glazing ratios or a change of unit mix all affect the calculation, and an energy statement based on the superseded layout no longer describes the building.
The original statement was prepared against an earlier Building Regulations edition. A statement demonstrating a percentage improvement against the 2013 baseline says nothing useful about a building that will be built to the current standard, and the arithmetic is where the confusion starts rather than ends.
The local plan has moved. A scheme consented under a policy requiring a modest on-site reduction, varied under a plan requiring net zero or a higher percentage, puts the officer in a difficult position which they will resolve by asking you to address the current policy.
Building Regulations do not follow the planning route
This is the distinction that saves the most time in these conversations, and it is routinely misunderstood on both sides.
The Building Regulations standard that applies to your building is determined by the building control route and timing, not by the planning permission. Transitional arrangements turn on when plans were deposited or an initial notice given and whether work started within the relevant period. A section 73 permission does not reset that position, and it does not, by itself, oblige you to build to a newer edition of Approved Document L.
What the planning system can do is impose a condition requiring performance beyond the Building Regulations minimum. That is where local policy operates, and it is the only lever the authority has. Saying so plainly, early, narrows the discussion to the right question: what does the development plan require of this permission, rather than which Part L applies.
Keep the two threads separate in your submission. A short note explaining the Building Regulations position, and a separate assessment addressing the development plan policy, is clearer than one document trying to do both.
What to submit, and at what depth
| Scale of variation | Proportionate energy evidence |
|---|---|
| Drawing number or minor internal change | A technical note confirming the approved performance is unaffected |
| Unit mix change, same envelope | Updated calculation summary, same methodology, with a comparison table |
| Change to envelope, glazing or floorspace | Full updated energy statement against current policy |
| Change to the energy strategy itself | Full statement, plus any carbon offset recalculation |
| Structural change on a referable scheme | Updated whole life carbon and circular economy evidence |
The middle row is where most schemes sit and where most money is wasted. A comparison table showing the approved figures, the revised figures and the delta, with the modelling assumptions stated, is usually enough. Commissioning a new assessment from scratch, with a new baseline and a new set of assumptions, invites a conversation about everything rather than about the variation.
Where the original consent was outline, the position is different again, because the carbon commitments may sit in a framework document rather than in a fixed design, and the mechanics of carbon reporting in an outline planning application determine what a variation actually changes.
Fabric performance is the part most likely to be scrutinised, since it is the part that survives a change of services strategy. The u-values and the junction details you commit to are the figures an officer can check later, which is why the u-values officers look at deserve attention in the comparison rather than a headline percentage alone.
London and the offset recalculation
On schemes referable to the Mayor, and on many borough schemes, an energy assessment follows a prescribed format and the residual carbon is paid for through a cash-in-lieu offset contribution. Where a variation increases floorspace or changes the energy strategy, the offset calculation changes with it.
Expect the Greater London Authority and the borough to ask for an updated assessment in the current template, with the offset recalculated and the planning obligation varied accordingly. Where the variation reduces floorspace, the same logic works in your favour, and it is worth running the calculation rather than assuming the original figure stands.
Structural changes on a referable scheme bring the embodied carbon evidence back into scope too. A Whole Life Carbon Assessment prepared for the original consent will need updating where the frame, substructure or facade system changes, and the result often moves more than the operational figures do.
Overheating is the one that catches residential variations. Increasing glazing or changing unit layouts alters the dynamic modelling, and an Overheating Risk Assessment prepared for the approved layout may no longer hold. Officers have become noticeably more alert to this.
Choosing the right route
Three routes exist and the choice is usually commercial rather than legal.
A section 96A non-material amendment does not create a new permission and cannot be used for anything material. It is quick, it carries a low fee, and it will not carry a change that affects the energy position, because a change that affects the energy position is not non-material.
A section 73 variation creates a new permission and reopens the conditions. Use it where the change is material but the description of development still fits.
A fresh full application starts from today's policy framework entirely. That sounds worse and sometimes is not, particularly where the original permission carries conditions you would rather be rid of, or where the description of development needs changing anyway.
Model all three before choosing. A section 73 that triggers a full policy update on a scheme with marginal viability can cost more than the variation delivers.
Scope it with the officer first
Write to the case officer before you submit, setting out precisely which condition you want varied, why the change is needed, and what energy evidence you propose to provide. Ask them to confirm whether that scope is acceptable.
Officers answer that question, and a written answer is worth having on the file. Where they ask for more than the variation justifies, the six tests and the limits on what could lawfully have been imposed on the original permission are the arguments to make, politely and in writing.
This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it.
Enter your postcode on PlanScope to draft the energy and carbon documents your variation needs, then send them for professional review. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.
Frequently asked questions
Why does a section 73 application reopen my energy statement?
Because section 73 grants a new planning permission, and the authority decides what conditions that new permission should carry in the circumstances existing now. Where the original condition referenced an approved energy statement by date, the authority has to settle what the equivalent condition should say, which brings current development plan policy into play.
Does a section 73 permission change which Part L applies?
No. The Building Regulations standard is determined by the building control route and timing, through the transitional arrangements based on when plans were deposited or notice given and whether work started. A section 73 permission does not reset that. Planning can only require performance beyond the Building Regulations minimum, through a condition.
Can a section 73 change the description of development?
No. The Court of Appeal decision in Finney v Welsh Ministers established that a section 73 cannot be used to vary a condition in a way that conflicts with the operative part of the permission. Where the change in substance alters what was permitted, a fresh application or another route is needed.
How much energy evidence should I submit with a variation?
Match it to the change. A drawing number amendment needs a technical note confirming the approved performance is unaffected. A unit mix change with the same envelope needs an updated calculation summary with a comparison table. A change to the envelope, glazing or floorspace needs a full updated statement against current policy.
Will my carbon offset payment be recalculated?
In London, usually yes, where the variation changes floorspace or the energy strategy. Expect a request for an updated assessment in the current template with the offset recalculated and the obligation varied. Where the variation reduces floorspace the same logic can reduce the contribution, so run the calculation rather than assuming.
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.