Fabric or technology: value engineering after permission
Swapping glazing or cutting a solar array after permission can breach the condition tied to the approved energy statement. The recalculation, the routes and the timing.
If your permission carries a condition requiring the development to be built in accordance with the approved energy statement, then swapping triple glazing for double, halving the photovoltaic array or changing a heat pump for direct electric heating is a breach of that condition. Not a variation to be sorted out at completion. A breach, enforceable by notice, and one that building control sign-off does nothing to cure. Value engineering an energy condition is a planning matter before it is a commercial one.
The pattern repeats on almost every scheme. The energy statement is written to win the permission, the contractor prices the job, and the savings come out of the specification nobody on site treats as a planning document.
How the approved energy statement binds the build
Conditions come in three forms and the wording decides how much room you have.
A condition requiring development in accordance with a named and dated energy statement makes the whole document a specification. Every U-value, every system efficiency and every stated renewable capacity becomes a planning requirement.
A condition requiring a specified percentage improvement over the Building Regulations baseline is outcome based. You can change how you get there, provided the recalculated figure still meets the number.
A condition requiring details to be submitted and approved before a defined stage leaves the specification open until you submit it, which is the most flexible position and the one worth negotiating for at the decision stage.
Read your condition before assuming which situation you are in. An Energy Statement that is approved as a document is harder to depart from than one whose target is written into the condition.
Substitutions that breach a condition
The substitutions that cause problems share a feature: they change an input the modelling relied on.
| Change at tender | Why it matters to the condition |
|---|---|
| Glazing specification relaxed | Alters both heat loss and solar transmittance, so it moves the regulated carbon figure and the overheating result |
| Photovoltaic capacity reduced | Directly removes the renewable contribution the percentage improvement depended on |
| Heat pump replaced with direct electric | Changes the system efficiency used in the calculation, usually by a large margin |
| Mechanical ventilation with heat recovery replaced with extract only | Removes a heat recovery credit and affects the ventilation strategy |
| Air permeability target relaxed | Changes the fabric heat loss input and the as-built test obligation |
| Wall or roof construction changed for buildability | Alters U-values and may alter thermal bridging values |
What does not usually breach a condition is a change of manufacturer where the performance figures are equal or better. Document that equivalence at the time rather than reconstructing it later, with the product data alongside the approved figures.
Recalculating after a specification change
The sequence is the same whichever route you end up taking.
- Freeze the proposed as-built specification, with each parameter the model needs: U-values by element, thermal bridging approach, air permeability, glazing solar transmittance, system efficiencies, renewable capacity and ventilation type.
- Re-run the compliance calculation on that specification, using the same methodology and version as the approved statement so the comparison is like for like.
- Compare the resulting percentage improvement over the baseline against the figure the condition or the policy requires.
- Re-run the overheating assessment, because glazing and ventilation changes move that result and a scheme can meet its carbon target while failing on summer comfort.
- Prepare a short comparison table showing approved against proposed for every parameter, with the resulting figures at each stage of the energy hierarchy.
That table is the document that settles the matter with an officer. Without it, the conversation becomes a negotiation about intent rather than a check of arithmetic.
When a section 73 variation is needed
Where the recalculated figure still meets the requirement, a discharge of conditions application or a written agreement with the case officer is normally enough, depending on how the condition is worded.
Where the figure falls short, or where the approved document itself has to be replaced, a section 73 application to vary the condition is the orthodox route. It creates a new permission with the condition amended, and it brings consequences worth planning for: the whole condition set is reconsidered, the community infrastructure levy liability is recalculated, and the application is publicised and consulted on again.
A non-material amendment under section 96A is sometimes offered as a quicker alternative. It works for minor changes and it does not work for a change in the carbon performance a policy required, because that is not non-material by any sensible reading. The Levelling-up and Regeneration Act 2023 inserted a new route for varying permissions, and whether it is in force, and its scope, should be checked against the current position before relying on it.
Where the overheating result moves as well, the assumptions set out in our note on overheating assessment assumptions decide whether the revised scheme still passes.
Evidence the council will want
Councils and their sustainability officers ask for the same four things.
The comparison table, approved against proposed, parameter by parameter. The recalculated compliance output as produced by the software, not a summary of it. A statement of why the change is proposed, which is usually buildability, supply chain or cost, said plainly. And where there is a shortfall, what makes it up: additional renewables elsewhere, a fabric improvement, or a carbon offset payment where the local policy provides for one.
Offset payments are set locally and the rate per tonne is published by the authority, so take the figure from the current schedule rather than from a previous scheme. Where the policy includes a monitoring and reporting requirement at as-built stage, the recalculated figures feed that submission too.
Where the change frees up or consumes roof area, the competition between plant, panels and green roof needs resolving again, and the roof space competition is usually the hardest part of a late redesign.
Timing against the build programme
This is where money is lost. A discharge of conditions application takes around eight weeks. A section 73 application takes around eight weeks for a minor development and longer for a major, plus consultation. Neither can be started usefully until the recalculation exists.
So a substitution identified at tender, which is typically three to five months before the relevant element is installed, is manageable. The same substitution identified on site, after the windows are ordered, is not. The practical rule is that any change to a modelled parameter needs the planning route confirmed before the order is placed.
And the worst outcome, which happens more often than it should, is a scheme completed to a specification that breaches the condition, discovered during the as-built assessment. At that point the choices are retrofitting renewables, buying an offset the policy may not permit after the event, or applying retrospectively and hoping.
Avoiding the problem at tender
Three measures remove almost all of this risk.
Write the modelled parameters into the employer's requirements as performance figures rather than named products, so a tendering contractor can substitute products while meeting the performance. Include a change control clause requiring any proposed substitution affecting a listed parameter to be re-modelled and cleared with the planning consultant before it is accepted. And have the energy consultant retained through construction rather than discharged at planning, so the recalculation takes days instead of weeks.
Then keep one register, held by the project manager, of every parameter the permission depends on. A Sustainability Statement and a Whole Life Carbon Assessment often contain commitments of their own, and those get forgotten more readily than the carbon figure because nobody is testing them at completion.
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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
Does building control sign-off cure a planning breach?
No. The two regimes are separate. A completion certificate confirms compliance with the Building Regulations and says nothing about whether the development was built in accordance with a planning condition. A condition tied to an approved energy statement remains enforceable regardless of the building control position.
Which substitutions actually breach the condition?
Those that change an input the modelling relied on: glazing specification, photovoltaic capacity, heat generator type and efficiency, ventilation type, air permeability target and element U-values. A change of manufacturer with equal or better performance figures generally does not, provided the equivalence is documented at the time.
Can I use a non-material amendment instead of section 73?
Only for minor changes. A reduction in the carbon performance that a local policy required is not non-material on any sensible reading, so section 96A is the wrong route. The 2023 Act inserted a further variation route, and whether it is in force should be checked first.
What does a section 73 application bring with it?
A new permission with the condition amended, which means the whole condition set is reconsidered, the community infrastructure levy liability is recalculated, and the application is publicised and consulted on again. Allow around eight weeks for a minor development and longer for a major scheme.
What evidence does a council want for the change?
A parameter-by-parameter comparison table of approved against proposed, the recalculated compliance output as the software produced it, a plain statement of why the change is proposed, and where there is a shortfall, what makes it up through additional measures or an offset payment at the authority's current published rate.
How do I stop this happening at tender?
Write the modelled parameters into the employer's requirements as performance figures rather than named products, add a change control clause requiring re-modelling and planning clearance before any substitution affecting those parameters is accepted, and keep the energy consultant retained through construction.
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.