Primary energy rate against emission rate in policy
Local plan carbon policies rarely say which Part L metric they mean. Emissions and primary energy diverged once grid carbon factors fell, so the baseline has to be stated before a percentage means anything.
When a local plan asks for a percentage improvement on Part L, the first question to settle is which number the percentage applies to. Approved Document L 2021 sets three targets for a dwelling, and two of them are plausible candidates for a primary energy rate planning policy: the target emission rate, measured in carbon dioxide per square metre per year, and the target primary energy rate, measured in kilowatt hours of primary energy per square metre per year. They move in different directions depending on the heating system, so the same scheme can show a comfortable improvement on one and a marginal one on the other.
Most adopted policies were drafted when only carbon existed as a metric. That is the root of nearly every argument on this subject.
The metrics the regulations now set
Approved Document L Volume 1 requires a new dwelling to beat three targets: emissions, primary energy and fabric energy efficiency. Volume 2 applies an equivalent structure to buildings other than dwellings. Primary energy was introduced as a headline compliance metric in the 2021 edition, having previously sat in the background.
The distinction matters because the two metrics answer different questions. Emissions reflect the carbon intensity of the fuel at the point of use, as modelled in the calculation methodology. Primary energy reflects the energy that had to be generated, transmitted and delivered to produce that unit of useful energy, so it captures grid losses and conversion inefficiency.
Grid decarbonisation pulled those two apart. The carbon factor for grid electricity in the current calculation methodology is far lower than in earlier versions, while its primary energy factor remains above one. An all-electric scheme therefore reads as a strong carbon performer and a weaker primary energy performer, and a gas scheme does something close to the reverse.
Why a percentage improvement needs a stated baseline
A policy requiring "a 20 per cent improvement over Part L" is incomplete in three ways at once. It does not say which edition of Part L. It does not say which metric. And it does not say whether the comparison is against the notional building for the actual scheme or against a separately modelled baseline building.
Those three unknowns compound. An improvement measured on emissions against the 2013 edition is a different exercise from an improvement measured on primary energy against the 2021 edition, and the arithmetic can differ by tens of percentage points for the same building.
The practical consequence is that the applicant chooses, and then has to defend the choice. State the edition, state the metric, state the comparator, and show the calculation. An Energy Statement that does all four is very hard to argue with, while one that announces a percentage with no stated basis invites a request for further information at week four.
How changed carbon factors shifted the arithmetic
The 2021 uplift to Part L was introduced with a stated ambition of around a 31 per cent reduction in carbon emissions for new dwellings and around 27 per cent for other new buildings, relative to the previous edition. Those figures do the heavy lifting in any argument about an older policy.
If a local plan adopted in 2017 requires a 19 per cent improvement on Part L 2013, a scheme that merely complies with Part L 2021 already exceeds that policy requirement on emissions by a wide margin. The policy's purpose has been met by national regulation catching up. Say so plainly, show the arithmetic, and do not volunteer an additional improvement against the current edition unless the policy actually asks for it.
The inverse case is the one to watch. Where a plan was adopted recently and expresses its requirement against the 2021 edition, the headroom has already been spent by the regulations and the remaining improvement has to come from fabric, from renewables or from heat pump efficiency that can be evidenced.
| Policy wording | What it probably means | What to pin down |
|---|---|---|
| Improvement over Part L, no edition | The edition current when the plan was examined | Confirm the edition in writing with the officer |
| Reduction in regulated carbon emissions | Dwelling emission rate against target emission rate | Whether unregulated loads are included |
| Reduction in primary energy | Dwelling primary energy rate against target | Whether the policy intended this or inherited it |
| Net zero carbon with on-site minimum | On-site reduction plus offset for the residue | The offset rate and the period it covers |
Reading a local policy for which metric it uses
Read the policy, then read the reasoned justification and the evidence base behind it, because the supporting text usually reveals the metric even where the policy does not. A policy sourced from a carbon study commissioned in 2018 almost always meant regulated carbon dioxide.
In London the position is set by the London Plan 2021, where the energy hierarchy of be lean, be clean, be green and be seen is applied and major development must achieve a minimum on-site reduction beyond building regulations with the shortfall offset. The Greater London Authority publishes guidance on how its policies apply following the 2021 Part L changes, and that guidance has been revised, so check the current version rather than the one you used last year.
Outside London, the pattern is more varied. Some authorities have adopted supplementary guidance clarifying the metric. Others have not, and the answer comes from pre-application correspondence.
Where a policy predates the current regulations
Section 1 of the Planning and Energy Act 2008 lets local authorities include policies imposing reasonable requirements for energy efficiency standards that exceed building regulations. That power is the legal basis for most of these policies, and it has been qualified by national statements over the years, including a written ministerial statement in December 2023 on local energy efficiency standards which indicated that authorities should not set standards beyond current or planned building regulations without a well-reasoned and costed justification. Verify the current position before relying on it, because this area has moved more than once and further change has been signalled.
For a consultant, the practical use of all this is narrow. An old policy with an old baseline is usually satisfied by compliance with the current regulations, and saying so with the arithmetic attached is faster than negotiating an enhanced specification nobody asked for.
Arguing the point with an officer
Four questions, asked at pre-application, settle it before the application is drafted.
- Which edition of Approved Document L is the baseline for this policy.
- Is the percentage measured on regulated carbon dioxide, primary energy or both.
- Is the comparator the notional building generated for this scheme or a separately modelled baseline.
- Does any offset payment apply to the residual, and at what rate and for what period.
Put the answers in writing. Officers change, and a figure agreed verbally in February is worth nothing at committee in November. Where the officer cannot answer, state your interpretation in the energy statement with reasons, which shifts the burden to the authority to disagree in terms.
And be willing to be told no. Where a policy is clear and recent, arguing about metrics is a poor use of fee when the design answer is a heat pump and a larger array.
Recording the baseline in the statement
One paragraph near the front of the energy statement, stating the policy, the edition, the metric, the comparator and the result. Then the calculation, then the measures that deliver it, in hierarchy order.
Keep the energy statement consistent with anything else in the submission that quotes a carbon figure. A Whole Life Carbon Assessment reports operational carbon in modules B6 and B7 on different boundaries from a regulated-emissions calculation, and two documents quoting different operational figures without explanation is the sort of inconsistency a committee report picks up. The same discipline applies to non-residential work, where the baseline question behaves differently again, as set out in our note on energy statements for warehouse and logistics schemes.
Where a draft is produced from structured inputs, keep anything unverified visibly flagged rather than filled in with a plausible number. A reviewer can work with a gap. A wrong baseline survives into the committee report.
This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. To see which supporting documents a scheme is likely to need, enter your postcode on PlanScope.
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 is the difference between the emission rate and the primary energy rate?
The emission rate measures carbon dioxide per square metre per year from regulated energy use, using the carbon factors in the current calculation methodology. The primary energy rate measures the energy that had to be generated and delivered to supply that use, so it captures grid losses. Electricity scores well on carbon and less well on primary energy.
Does complying with Part L 2021 satisfy an older local policy?
Often yes, on carbon. The 2021 uplift was introduced with a stated ambition of around 31 per cent lower emissions for new dwellings and around 27 per cent for other buildings against the previous edition. A policy asking for a smaller improvement on the 2013 baseline is therefore usually met by compliance alone, with the arithmetic shown.
Which metric should I use if the policy does not say?
Read the reasoned justification and the evidence base behind the policy, which usually reveals the metric even where the policy text does not. A policy drawn from a carbon study written before 2021 almost always meant regulated carbon dioxide. Confirm your reading with the case officer in writing and record it in the energy statement.
Can a council require standards above building regulations?
Section 1 of the Planning and Energy Act 2008 allows local plan policies to impose reasonable energy efficiency requirements exceeding building regulations. National statements have qualified how far that goes, including a written ministerial statement in December 2023 on local energy efficiency standards. Verify the current position, because this area has changed more than once.
How do I keep the energy statement consistent with a carbon assessment?
State the boundary each document uses. A whole life carbon assessment reports operational energy in its in-use modules on a different basis from a regulated emissions calculation, so the two figures will differ legitimately. Explain why in both documents, because unexplained differences get picked up in the committee report.
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.