Two regimes on one set of numbers
Everywhere in England a new dwelling needs a SAP calculation to satisfy Part L — checked by Building Control, reported as the DER against the TER, finished off with an EPC. London adds a second regime that uses the same calculation for a different purpose. Under the Planning and Energy Act 2008, a planning authority may require development to exceed Building Regulations, and London’s does: the London Plan sets a carbon target above Part L and boroughs add their own on top. That is a planning condition, tested at application stage, not a Building Control matter.
So a London scheme usually needs the SAP run in two ways. Once as Building Control will see it. And once for the planners, staged through the London energy hierarchy — Be Lean (fabric and efficiency), Be Clean (heat networks and local energy), Be Green (on-site renewables), Be Seen (in-use monitoring) — to show what each step achieves against the baseline. The two submissions have to agree with each other. When they come from different people, they frequently don’t.
The London Plan: majors, 35%, and cash
London Plan Policy SI 2 requires major development — ten or more dwellings, a site of half a hectare or more, or 1,000 m² of other floorspace — to be net zero-carbon, and sets a minimum on-site reduction of at least 35% beyond Building Regulations. Since 1 January 2023 that baseline is Part L 2021, which made the 35% materially harder than the same figure was against Part L 2013. The GLA’s own guidance says residential schemes should be aiming for 50% or more.
Within the 35%, at least 10% for residential (15% non-residential) must come from energy-efficiency measures alone — the Be Lean stage — before renewables are counted. That rule exists to stop schemes buying compliance with solar panels on a leaky building.
Whatever is left between the on-site reduction and net zero is offset: a cash payment into the borough’s carbon offset fund, calculated on the residual tonnes of CO₂ per year over 30 years. The GLA’s recommended price is £95 per tonne, which comes to £2,850 per tonne of annual residual emissions — and several boroughs charge more (below). On a mid-sized scheme the offset payment is a line item worth designing against.
Major schemes also submit a full energy assessment to the GLA’s Energy Assessment Guidance, including the GLA Carbon Emissions Reporting Spreadsheet with SAP or BRUKL outputs at each stage of the hierarchy; must address overheating through the cooling hierarchy with TM59 modelling under Policy SI 4 (that is in addition to Part O at Building Control, not instead of it); and carry a Be Seen obligation to report in-use energy performance for at least five years after completion, normally through a Section 106 agreement. Schemes big enough to be referred to the Mayor — 150 homes or buildings over 30 m — add a whole-life carbon assessment.
Below ten homes: it depends on the borough
The London Plan’s 35% is written for majors. Nothing in it requires a scheme of six flats or one house to beat Part L. The borough’s Local Plan usually does, and the boroughs disagree with each other. The ones we can vouch for, as they stand in September 2026:
- Merton — minor residential schemes (1–9 dwellings) must achieve a 35% improvement on Part L 2021 on site, submitted on Merton’s own template for minor residential schemes rather than a full statement, with residual emissions offset at £300 per tonne over 30 years. Merton also sets a space heating demand target and requires 105 litres per person per day for water.
- Wandsworth — all non-major new residential development should achieve a 35% on-site reduction below Part L 2021, with a 10% minimum from energy efficiency, under Policy LP10.
- Haringey — energy statements are required for 1–9 new dwellings, and the policy is zero carbon: a 100% reduction against Part L 2021, with at least 20% from on-site renewables and offsetting for the rest.
- Camden — an energy statement for every new-build dwelling, and for any development of five or more dwellings or 500 m².
- Tower Hamlets — 45% over Part L 2021 for major schemes, above the London minimum, offset at £95 per tonne.
- Westminster — a new City Plan adopted in January 2026: 35% for majors with a 50% residential benchmark, a retrofit-first policy requiring demolition to be justified, and offset prices of £330 per tonne (electric) and £880 (gas).
- Kensington and Chelsea — major developments must be net zero-carbon, offset at £2,850 per tonne (£95 × 30 years), under Policy GB4.
- Islington — a sustainable design and construction statement for all development creating new dwellings, proportionate to its size, under the Climate Action SPD adopted September 2025.
- Barnet — the outlier. Its Local Plan (adopted March 2025) references the Mayor’s energy hierarchy but expressly follows the December 2023 ministerial statement that local policies should not exceed Building Regulations. Part L is the test.
- Hammersmith and Fulham — a draft policy would ask 35% of all non-major schemes, but it is a consultation draft, not adopted, and carries little weight yet.
Two boroughs with a common boundary can want entirely different things from the same drawings. Tell us the borough before anything else.
What we do on a London job
Run the SAP as Building Control needs it. Run the Be Lean and Be Green scenarios and complete the GLA spreadsheet or the borough’s template. Write the energy statement, or the short-form version, to the borough’s own policy wording — see our energy statements service for the planning side in full. Tell you what the offset payment is likely to be while there is still time to reduce it. And keep one model behind all of it so the planning and Building Control submissions say the same thing.
London also puts more of your sites into Part O’s high-risk category — central and inner London postcodes have tighter glazing limits and a mandatory shading requirement — and the London Plan’s 105 litres per person per day water standard is tighter than Part G’s default. Both are on the Part O and London water calculation pages.
What is about to change
Two things, on two timetables.
The London Plan. A draft new London Plan was published on 16 July 2026; consultation runs to 15 October 2026, with adoption expected in early 2028. It abolishes the 35%-beyond-Part-L model and the carbon offset fund, replacing them with absolute targets under a new Policy GHR1: an energy use intensity of 40 kWh/m²/yr (35 aspirational) and a space heating demand of 20 kWh/m²/yr (15 aspirational) for homes, with five years of in-use reporting kept. Until adoption, the London Plan 2021 applies in full — and boroughs that already work in absolute terms, as Merton does, are ahead of it.
Building Regulations. The Future Homes Standard comes into force on 24 March 2027, with transitional cover for schemes submitted to Building Control before then and started by 24 March 2028. The GLA has not yet said how, or whether, the 35% will be rebased against it. We’ll tell you when it does.
Send the drawings and the borough — get a quote or call 01202 623236.
Common questions
Is a SAP calculation in London different from the rest of England?
The SAP itself is the same — Part L 2021, assessed for Building Control. What is different is that London planning runs a second test on the same numbers. The London Plan requires major developments to be net zero-carbon with at least a 35% on-site reduction beyond Part L, demonstrated in an energy statement at planning stage, and many boroughs apply their own version of that to schemes as small as one dwelling. So a London SAP usually has to be run twice over: once as Building Control sees it, and once as Be Lean and Be Green scenarios for the planners.
What is the 35% rule?
London Plan Policy SI 2 requires major development — ten or more dwellings, or a site of half a hectare — to achieve a minimum on-site reduction of at least 35% in regulated carbon emissions beyond Part L, measured against the Part L 2021 baseline for applications made since 1 January 2023. At least 10% of that must come from energy-efficiency measures alone for residential (15% non-residential). The GLA says residential schemes should be aiming for 50% or more. Whatever remains between 35% and net zero is offset with a cash payment to the borough.
How much is the carbon offset payment?
The GLA's recommended price is £95 per tonne of CO2 for 30 years — £2,850 per tonne of annual residual emissions — and most boroughs use it. Some do not: Lewisham charges £104, Merton £300, and Westminster £330 per tonne for electric and £880 for gas, all over 30 years. Fifteen more boroughs are reviewing their price. Check the borough's current figure, not the London Plan.
Does the 35% apply to a scheme of fewer than ten homes?
Not under the London Plan, which is written for major development. But it very often applies under the borough's own Local Plan. Merton and Wandsworth require 35% from minor residential schemes; Haringey requires them to be zero carbon; Camden requires an energy statement for every new-build dwelling. Other boroughs ask for nothing beyond Part L. Which borough you are in decides the answer, so tell us first.
What is an energy statement, and do I need one?
The planning document that shows how the scheme follows the London energy hierarchy — Be Lean, Be Clean, Be Green, Be Seen — and hits its carbon target. For major schemes it follows the GLA's Energy Assessment Guidance and includes the GLA Carbon Emissions Reporting Spreadsheet with SAP outputs at each stage. Boroughs set their own thresholds for smaller schemes, and several want a simplified template rather than a full statement. We produce both.
What is Be Seen?
The last step of the London energy hierarchy: monitoring. Major developments must report actual in-use energy performance to the GLA's portal every year for at least five years after completion, usually secured by a Section 106 agreement. It means the numbers in the energy statement get checked against reality, which is one reason the GLA wants them realistic.
Is London about to change the rules?
Yes. A draft new London Plan was published on 16 July 2026, with consultation to 15 October 2026 and adoption expected in early 2028. It drops the 35%-beyond-Part-L model and the offset fund in favour of absolute energy targets — 40 kWh/m²/yr energy use intensity and 20 kWh/m²/yr space heating demand for homes. Until it is adopted the London Plan 2021 applies in full. Separately, the Future Homes Standard comes into force for Building Control on 24 March 2027.