Phasing energy and carbon obligations on a large site
Fix infrastructure and methodology at outline, then tie each phase to the standard in force when it is designed. Offset payments belong phase by phase.
Phasing energy obligations across a large site means writing a strategy at outline stage that will still make sense when phase six comes forward eight years later, under a version of Part L that has not been published yet. The two failure modes are symmetrical. Conditions that lock the scheme to today's standard become obsolete and sometimes unbuildable. Conditions that float entirely leave the authority with nothing to enforce and the developer with no certainty on cost.
The workable answer is a strategy fixed at outline on the things that are structural, with the performance standard tied to a defined point in time for each phase.
What an outline permission can realistically fix
Three categories of decision belong at outline, because they constrain everything afterwards.
Infrastructure comes first: the location and size of any energy centre, the primary pipe routes, substation positions and capacity, and the safeguarded space for a future network connection. These occupy land and cross phase boundaries, so leaving them to reserved matters means a later phase discovering that the route runs through a consented block. Our note on safeguarding a future heat network connection sets out the reservations worth making.
Second is the hierarchy and the approach. Whether the site is served by individual systems, a site wide network, or a hybrid. Whether the strategy relies on heat pumps, and if so what that means for electrical capacity, which is a grid connection question with lead times measured in years.
Third is the measurement framework: what metric performance is assessed against, what baseline is used, how reductions are reported, and who verifies them. Agreeing the framework at outline avoids an argument about methodology at every reserved matters application.
What cannot sensibly be fixed at outline is the detailed specification of buildings that have not been designed, or a numerical reduction target expressed against a baseline that will be superseded.
Which standard applies to phase six
This is the question that matters commercially, and the answer should be in the condition rather than left to negotiation.
| Drafting approach | Effect | Risk |
|---|---|---|
| Standard fixed at the date of the outline permission | Certainty of cost | Becomes obsolete, and may conflict with later building regulations |
| Standard in force when each reserved matters application is submitted | Tracks policy | Cost uncertainty across phases |
| Standard in force at the building regulations application for each plot | Tracks regulation closely | Weak planning control, hard to monitor |
| Higher of the outline standard and the standard then in force | Protects the authority | Developer carries all the upside risk |
| Phase review mechanism with a defined trigger and scope | Balanced | Needs careful drafting to avoid a reopening of everything |
Most authorities will push for the fourth option and most developers should argue for the second with a review mechanism. The argument for the second is straightforward: the applicant designs to the policy and regulations applicable when the phase is designed, which is what every other part of the construction industry does.
The relationship between planning policy and building regulations deserves a sentence here. Energy performance for new homes has been contested ground between national regulation and local policy for years, including the position set out in the written ministerial statement of March 2015 and the subsequent changes to Part L. The position has moved more than once, so verify where it stands when you draft, and record the date you verified it (position as at October 2026).
Drafting conditions that survive a decade
- Tie each obligation to a defined phase, with the phases shown on a plan approved as part of the outline permission.
- Use a trigger that exists on the ground, such as submission of the reserved matters application for a phase, rather than a calendar date.
- Name the document to be submitted, for example a phase energy statement, and say what it must contain as a list.
- State the baseline and the methodology, and allow for a successor methodology where the named one is withdrawn.
- Include a response period for the authority, because a phase cannot wait eight weeks for every variation.
- Allow substitution of an equivalent or better technology on a stated test, approved in writing.
- Say what verification is required at completion and who pays for it.
- Avoid conditions that require approval of matters already controlled by building regulations, because they fail the necessity test and create duplicate processes.
An Energy Statement prepared for each phase under that framework is a short document, because the strategic work was done once at outline. That is the point of phasing it properly.
Offset payments phase by phase
Where policy requires carbon offset payments for residual emissions, the mechanism usually sits in the section 106 agreement rather than in a condition. In London the London Plan sets a net zero-carbon target for major development with a minimum on-site reduction beyond the Part L baseline, and a cash in lieu contribution to the borough's offset fund for the shortfall, calculated over a 30 year period at a price per tonne the borough sets and reviews. Check the current price, because it is updated.
For a phased site, the drafting points are these. Calculate the payment per phase, at the time that phase is designed, using the price then current. Set the trigger on commencement of each phase, not on the first phase. Index the figures. And include a reconciliation at post-construction stage, because the as-built performance will differ from the design stage calculation.
Resist a single payment calculated at outline for the whole site. It fixes a liability against an uncertain design and almost always produces a figure that neither side believes.
Illustrative example: a 900 home site in four phases agrees phase level energy statements at each reserved matters stage, offset payments calculated per phase at the price current when that phase is approved, with payment on commencement of each phase and a post-construction reconciliation within twelve months of the last completion in the phase. Figures are illustrative.
Changing technology mid-build
Between phase one and phase four the plant market will move. A condition naming a specific system makes a better option unlawful without a section 73 application, and three section 73 applications across a site is a poor use of everyone's time.
Draft the substitution clause now. A workable test requires the substitute to deliver equal or better regulated carbon performance, to be no worse on operational cost to the occupier, and to be compatible with the site infrastructure already built. Require a short technical note demonstrating each limb, approved in writing within a stated period.
Grid capacity is the constraint that most often forces a change. Where an all electric strategy depends on a connection offer, the offer has a validity period and a price that can change, and a strategy that cannot be delivered because the connection moved needs a route to amendment that does not stop the site.
Whole life carbon across phases
Where a Whole Life Carbon Assessment is required, an outline application can only ever produce an indicative figure, because quantities depend on design. Agree an outline level assessment with stated assumptions, then a phase level assessment at reserved matters and a post-construction update.
The useful discipline is to carry the assumptions forward explicitly. Where the outline assessment assumed a concrete frame and the phase comes forward in timber, the comparison tells a good story. Where it assumed timber and the phase is concrete, the authority will ask why, and having the assumption written down is better than having it inferred.
Detailing decisions interact with this, and our note on thermal bridging detail at planning stage covers the fabric side of the same argument.
Monitoring and reporting
Post-construction monitoring is increasingly a requirement rather than an aspiration. The London Plan expects energy performance to be reported after completion and in use, which means metering has to be designed in and someone has to collect the data for years.
Allocate that duty in the section 106 agreement, name the reporting format, set the frequency, and say what happens if performance falls short. A reporting obligation with no consequence and no named party is the clause everyone forgets, and an authority that discovers in year five that nobody has reported will raise it on the next phase.
Decide the standard-in-force question before you accept the outline conditions. Browse all 66 PlanScope report types to see which energy and carbon documents each phase is likely to need, and have any draft reviewed before submission.
PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. This is general guidance, not legal advice, so check the position with your local planning authority or a qualified professional before relying on it.
Frequently asked questions
What should an outline energy strategy fix?
Three things: infrastructure that crosses phase boundaries, including energy centre location, pipe routes, substation capacity and safeguarded space; the strategic approach, such as individual systems against a site wide network and the grid capacity it implies; and the measurement framework covering metric, baseline, reporting and verification.
Which energy standard applies to a later phase?
Whatever the condition says, which is why the drafting matters. The common options are the standard at the date of the outline permission, the standard in force when each reserved matters application is submitted, or the higher of the two. Tying it to the standard in force when the phase is designed is the position most developers should argue for.
Should a carbon offset payment be calculated at outline?
No. A single payment fixed at outline is calculated against an uncertain design and rarely convinces either side. Calculate per phase, at the price current when the phase is approved, with the trigger on commencement of that phase, indexation, and a post-construction reconciliation once as-built performance is known.
How do I allow for a change of technology between phases?
Include a substitution clause requiring the alternative to deliver equal or better regulated carbon performance, to be no worse on operational cost to the occupier, and to be compatible with infrastructure already built, demonstrated in a short technical note approved in writing within a stated period. Grid capacity is the usual reason a change is needed.
Who is responsible for post-completion energy monitoring?
Whoever the section 106 agreement names, which means someone has to be named. Metering must be designed in, the reporting format and frequency specified, and the consequence of shortfall stated. The London Plan expects performance to be reported after completion and in use, so plan for data collection over several years.
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.