Urban Greening Factor or biodiversity net gain units

If you are asking whether the Urban Greening Factor or biodiversity net gain applies to a London scheme, the answer is both, and they measure different things. The Urban Greening Factor under London Plan 2021 Policy G5 scores the weighted surface cover of your site against a target: 0.4 for predominantly residential development and 0.3 for predominantly commercial. Biodiversity net gain under the Environment Act 2021 counts habitat units before and after development and requires a 10 per cent uplift secured for at least 30 years.

One is a design ratio checked at determination. The other is a statutory condition with a post-permission approval stage and a long management tail. Treating them as one exercise is the mistake that produces a landscape drawing satisfying neither.

What each measure counts

The Urban Greening Factor divides the site into surface cover types, multiplies the area of each by a factor reflecting its greening value, adds the results and divides by the site area. Sealed surfaces score zero. Semi-natural vegetation and open water sit at the top of the scale. Everything else, including green roofs, rain gardens, hedges, trees in connected pits, amenity grassland and permeable paving, sits somewhere between, with the definitive factors set out in the Greater London Authority's published guidance. Use the current version of that table rather than a figure remembered from an earlier scheme, because it has been revised.

The statutory biodiversity metric works from habitat parcels instead of surface cover. Each parcel is scored on area, distinctiveness, condition and strategic significance, then adjusted for the time habitat creation takes and the difficulty of creating it, with a further reduction for off-site parcels according to how far away they are. The output is habitat units, not a ratio.

So one asks what proportion of your site is green and how good that green is. The other asks how much biodiversity value you are removing and whether you are putting back more than you took.

Surface cover scoring against habitat units

The two behave differently under pressure, and understanding how is worth an hour at concept stage.

The row that catches developers out is the fifth one. A high Urban Greening Factor score can be achieved with a lot of ordinary landscaping. A metric gain cannot, because the metric discounts low distinctiveness habitat heavily and rewards creating something better than what was there.

Which schemes are asked for each

Policy G5 applies to major development in London, and boroughs apply it through their own local plan policies as well. Outside London, some authorities have adopted a green space factor or urban greening requirement of their own, so read the adopted plan rather than assuming the requirement is London-only.

Biodiversity net gain applies far more widely. The biodiversity gain condition has applied to major development since 12 February 2024 and to small sites since 2 April 2024, with a short list of exemptions covering householder applications, self-build and custom build of up to nine dwellings on 0.5 hectares or less, and development affecting less than 25 square metres of on-site habitat.

A London major residential scheme therefore faces both, on different timetables. The greening score has to be right in the submitted drawings. The gain plan is approved after permission, but the baseline that drives it has to be surveyed and submitted with the application, so the ecology programme starts at the same time.

How a green roof scores in both

Green roofs are the clearest illustration of the divergence, and the reason so many schemes over-rely on them.

In the Urban Greening Factor, a green roof is productive. It counts towards the score at a factor that rises with substrate depth and planting quality, and on a tight urban site it may be the only way to reach 0.4 at all.

In the statutory metric, the same roof is a low distinctiveness urban habitat. It generates units, but modestly, and the condition assessment is strict about substrate depth, species diversity and management. Building a scheme's entire gain strategy on an extensive sedum roof usually produces a small positive number that any survey revision can wipe out.

The practical response is to specify the roof once, to a depth and species mix that works for both, and to record its area identically in the greening calculation and the habitat parcel plan. A biodiversity roof with 150 millimetres or more of varied substrate does real work in both systems. A thin sedum mat does very little in one of them.

Where the two pull the design apart

Four tensions show up repeatedly on constrained sites.

Amenity grassland is the first. Large lawns lift the greening score usefully and score poorly for distinctiveness, so a scheme optimised for the ratio can go backwards on units.

The second is podium landscaping. Vegetation over structure counts in the greening calculation, and the metric treats it as habitat only where the substrate depth and management allow the condition criteria to be met. Shallow planters full of ornamental shrubs are worth more to one measure than the other.

The third is off-site delivery. Net gain allows units to be bought or created elsewhere, subject to the spatial risk reduction and the statutory sequence. The greening factor has no off-site route at all, so it cannot be solved with money.

The fourth is retention. The metric rewards keeping an existing high-distinctiveness parcel far more than creating a new one, because creation carries temporal and difficulty penalties. The greening factor is indifferent to whether the vegetation is old or new, which is why a scheme can hit 0.4 while clearing the one patch of ground worth keeping.

Getting the Landscape Strategy and the ecology work onto the same drawing at concept stage is the only reliable fix. If they are drawn separately and reconciled at submission, the reconciliation usually involves losing units.

Securing each through conditions and obligations

The mechanisms are not comparable, and confusing them delays commencement.

The greening score is normally secured through a landscape condition requiring detailed planting, substrate specifications and sometimes a recalculated score against the approved drawings. It is a pre-occupation or pre-above-ground-works condition in most cases.

Biodiversity net gain is secured by the statutory biodiversity gain condition. Development cannot begin until the authority has approved a biodiversity gain plan, and on-site gains need a habitat management and monitoring plan running for at least 30 years, typically through a planning obligation or a conservation covenant. Off-site gains have to be registered and allocated to the development. This is a pre-commencement gate, not a discharge item you can leave until later.

A Biodiversity Net Gain Assessment under the Environment Act 2021 expects the statutory metric to be completed by a competent person, and the gain plan is approved by the local planning authority. An AI-assisted draft sets out the structure and the policy narrative. The metric file and the professional judgement behind it have to come from your ecologist. If you are still deciding which document you need, the difference between net gain work and a broader ecological assessment is set out in our note on biodiversity net gain or ecological impact assessment.

Reporting them in one submission

Use one base drawing, one area schedule and one set of surface definitions. Then produce two calculations from it.

State the site area used for the greening calculation and confirm it matches the red line. State the habitat parcels used for the metric and confirm their areas sum to the same site area. Where a surface counts differently in the two systems, say so in a footnote rather than adjusting one figure to make the two agree. And give the metric version number and the greening guidance version, because reviewers check both.

A Green Infrastructure Plan is a useful place to hold the shared narrative, with the two calculations appended as separate technical annexes.

Enter your postcode on PlanScope to see which reports a London major scheme is likely to need before you commission the surveys.

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