Energy strategy: Be Lean, Be Clean, Be Green, Be Seen

The London energy hierarchy has four steps, and the fourth one is the reason so many schemes come unstuck at condition discharge rather than at committee. Be Lean, Be Clean and Be Green are design decisions made before the application goes in. Be Seen is a commitment to report actual metered performance for years after the building is occupied, and it has to be set up in the planning documents even though nothing can be measured yet.

London Plan Policy SI 2 requires major development to be net zero-carbon, with a minimum on-site reduction beyond the Building Regulations target emission rate and any residual emissions dealt with through a cash contribution to the borough's carbon offset fund. The hierarchy is the order in which you are expected to get there, and applying it out of order is the commonest reason an Energy Statement is sent back.

The four steps and what each one demands

Be Lean reduces demand through the building itself: form, orientation, fabric performance, air tightness, glazing ratios, thermal bridging and efficient ventilation and lighting. Be Clean addresses how heat is supplied, which in London means the heating hierarchy in Policy SI 3 and the question of connection to a heat network. Be Green covers on-site renewable generation, in practice almost always photovoltaics. Be Seen is operational monitoring and public reporting.

Policy SI 2 also sets minimum contributions from the first step alone, higher for non-residential than for residential development, which stops an applicant meeting the overall target entirely with solar panels. Check the current percentages and the applicable baseline in the Mayor's energy assessment guidance, because the baseline moved when the 2021 Part L uplift took effect and the guidance has been revised since.

The sequence matters in the arithmetic as well as in principle. Each stage is modelled as a separate scenario, with regulated carbon emissions reported after Be Lean, after Be Clean and after Be Green, so the assessor can see what each step contributed.

Demand reduction before technology

The honest difficulty with Be Lean is that it competes with everything else in the design. Deep plans reduce surface area and heat loss, and worsen daylight. Smaller windows reduce overheating risk and solar gain, and attract objections on outlook and internal daylight, which is where the tension with the approach in our note on applying BRE 209 daylight guidance in dense London becomes real.

What a reviewer checks is consistency. If the energy model assumes a glazing ratio of 25 per cent, the elevations have to show 25 per cent. If it assumes an air tightness figure well beyond the regulatory backstop, the construction details have to be capable of delivering it and the applicant has to accept a condition requiring testing. Fabric values typed into the model to make the percentage work, with no corresponding change to the drawings, are the single most common finding when the GLA reviews a stage one submission.

Overheating is part of the same conversation. Policy SI 4 requires the cooling hierarchy to be applied, and dynamic thermal modelling to CIBSE TM59 for residential schemes is the expected evidence. An Overheating Risk Assessment that contradicts the energy model's assumptions about openable area or shading is worse than no assessment at all.

Heat networks and the connection question

Policy SI 3 sets a heating hierarchy, and the first question is whether the site falls within a Heat Network Priority Area. The London Heat Map is the tool for that, and the answer has to appear in the energy statement with the source cited rather than asserted.

Inside a priority area, the expectation runs in this order:

1. Connect to an existing or planned local heat network where one is available or committed.
2. Use zero-emission or local secondary heat sources, which in practice means heat pumps, with ambient loop arrangements increasingly common.
3. Only then consider lower-emission alternatives, with gas-fired combined heat and power now very hard to justify given air quality policy and the decarbonising grid.

Where no network exists but one is planned, safeguarding is the requirement rather than connection. That means a plant space sized and located for a future heat exchanger, a route reserved for the incoming pipework, a hydraulically separate secondary system, and distribution temperatures low enough to be compatible with a future network. Those are drawings and a commitment in the section 106 agreement, not a sentence in the statement.

Renewables and what the roof can actually hold

Be Green in London is a photovoltaic argument almost every time, and it is usually an area argument. The roof has to accommodate plant, lift overruns, a safe access zone, any green roof needed for the urban greening factor, and amenity space on buildings where that is where the amenity space went.

Show the panel layout on a roof plan with the other demands marked, and give the installed capacity, the orientation and the expected annual yield from the model. An energy statement that claims a percentage from renewables without a roof plan invites the reviewer to assume the panels will not fit, and they are often right.

Where the roof simply cannot take enough, say so and quantify the offset payment instead of inflating the generation figure. A carbon offset contribution calculated on the residual emissions over the period set in the Plan, at the price in the Plan or the borough's own adopted rate, is an accepted outcome. An overstated renewables figure discovered at as-built stage is a problem for the developer, because the shortfall still has to be paid for.

The Be Seen stage

Be Seen requires reporting of actual energy performance data through the Mayor's online portal, at three points: the predicted figures at planning stage, the as-built figures once construction is complete, and in-use metered data reported annually for a period after occupation.

What this means practically is that the application has to commit to the metering strategy. Sub-metering by end use and by tenure, access arrangements for reading the meters, and a responsible party named for the reporting period all have to exist. Retrofitting sub-metering into a completed block to satisfy a condition is expensive and sometimes impossible.

Expect the obligation to be secured by condition or by the section 106 agreement, with the reporting stages as triggers. Put the metering schematic and the nominated reporting party in the energy statement, and the discharge of that condition becomes administrative rather than contentious.

Referable schemes and the documents that travel with the statement

For applications referable to the Mayor, the energy statement arrives alongside a Whole Life Carbon Assessment prepared to the RICS methodology and a circular economy statement, both to the Mayor's published templates. The three documents share inputs, and inconsistency between them is noticed.

The frequent mismatch is between the whole life carbon assessment's assumed structural solution and the energy statement's assumed fabric build-up. A second mismatch sits between the circular economy statement's claims about retention and the demolition drawings. Allocate one person to reconcile the three sets of numbers before submission.

Capacity decisions upstream affect all of this, since massing drives surface-to-volume ratio, roof area and overheating risk at once. The approach in our note on optimising site capacity under Policy D3 is where an energy strategy should start rather than where it should be tested.

Where strategies fall short

Six failures account for most of the comments a GLA or borough energy reviewer writes.

The baseline is wrong, usually because an older Part L target emission rate was used. The Be Lean saving is claimed from fabric values the drawings do not support. The heat network priority area check is missing or unsourced. Combined heat and power appears without an air quality justification. The photovoltaic area is asserted with no roof plan. And Be Seen is mentioned in a single sentence with no metering strategy behind it.

None of these are difficult to fix at draft stage, and all of them are expensive to fix after a resolution to grant. Build the statement around evidence that a reviewer can check against the drawings, and the energy chapter of the committee report writes itself.

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 see which reports your scheme is likely to need.

PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval.