The biodiversity gain condition and who is exempt from it

Every planning permission granted in England now carries a biodiversity gain condition unless the development falls within one of a short list of exemptions. The condition is deemed, which means it applies whether or not the decision notice mentions it, and it prevents development beginning until the local planning authority has approved a biodiversity gain plan. For a self-builder with nine plots or fewer, the exemption that matters is the self-build one, and it has three limbs that all have to be satisfied.

The machinery sits in Schedule 7A of the Town and Country Planning Act 1990, inserted by the Environment Act 2021. The headline requirement is a 10 per cent gain in biodiversity value, measured using the statutory biodiversity metric, maintained for at least 30 years. Major development came into scope on 12 February 2024 and small sites on 2 April 2024.

What the deemed condition actually says

The condition prohibits the carrying out of development until a biodiversity gain plan has been submitted to, and approved by, the planning authority. It bites before any work starts, and it behaves like any other such condition: starting on site without approval is a breach, and the usual enforcement remedies follow.

The plan itself sets out the pre-development biodiversity value of the onsite habitat, the post-development value, any registered off-site gains and any statutory biodiversity credits, and shows that the total reaches the required uplift. It also identifies irreplaceable habitat, which is handled outside the metric through bespoke compensation agreed with the authority.

Two dates decide the pre-development baseline. The value is normally assessed as at the date of the application, though where habitat has been degraded after 30 January 2020 the authority can require the earlier, higher value to be used. That anti-avoidance provision catches sites cleared in anticipation of an application, and it is the reason a photographic record and a dated habitat survey are worth having before anyone brings in machinery.

The exemptions, in the order most people need them

The exemptions sit in the Biodiversity Gain Requirements (Exemptions) Regulations 2024 and in Schedule 7A itself.

• De minimis. Development that does not impact a priority habitat and impacts less than 25 square metres of on-site habitat, or less than 5 metres of on-site linear habitat such as a hedgerow or line of trees. Hard surfacing and buildings count as habitat with a value of zero, so a scheme confined to existing tarmac can fall under the threshold even when the building is large.
• Householder development. Extensions, outbuildings and alterations within the curtilage of a dwellinghouse, as defined in the regulations.
• Self-build and custom build. No more than nine dwellings, a site area of no more than 0.5 hectares, and dwellings that meet the statutory definition of self-build or custom housebuilding. All three conditions apply together.
• Development granted by a development order. Permitted development and prior approval routes fall outside the gain requirement, which is one of the practical differences between a Class Q conversion and a full application on the same barn.
• Biodiversity gain sites. Development on land already registered as a gain site, so that habitat banks are not caught by their own regime.
• Urgent Crown development and certain other categories set out in the regulations.

Section 73 permissions have their own treatment, and the position depends on when the original permission was granted and whether the earlier permission was itself subject to the gain requirement. If you are varying an older consent, check that alongside the section 73B route, because the choice of application route can change whether a gain plan is needed at all.

Where the de minimis test goes wrong

The test is about habitat area, not about development area, and those are different numbers. A single storey rear extension of 30 square metres built over an existing patio may affect almost no habitat. The same extension built over a lawn affects 30 square metres of modified grassland and fails the test.

Linear habitat catches more schemes than people expect. Five metres of hedgerow is a driveway width. Removing a hedge to form an access, even on an otherwise exempt scheme, puts the development back into the regime, and hedgerows are scored separately in the metric.

The safe approach on a small site is to have an ecologist walk the site and measure the habitat parcels before the layout is fixed. It is a short visit, and it converts an uncertain exemption claim into an evidenced one. Authorities do challenge de minimis claims, and the challenge usually arrives at validation, which is the worst point in the programme to lose three weeks.

Getting the numbers done properly

The statutory metric is a calculation tool, and using it is not the same as being able to defend the habitat classification behind it. Condition assessment, distinctiveness scoring and the strategic significance multiplier all involve judgement, and the Environment Act regime expects a competent person to carry it out. A biodiversity net gain assessment drafted with AI assistance is a structure for that person to work within, never a replacement for them.

Off-site units and statutory credits sit at the end of the hierarchy. On-site gain first, then registered off-site units, then credits from the government as a last resort at a deliberately unattractive price. Authorities will ask what was tried on site before an off-site solution is proposed, and a layout that never considered on-site habitat is a weak starting point.

The 30-year management obligation is secured through a section 106 agreement or a conservation covenant, with monitoring reports at set intervals. That is a long-term liability on the land, so it belongs in the appraisal and in any sale documentation.

An illustrative check

Illustrative example. A plot of 0.18 hectares for four self-build homes on a former paddock. Site area and dwelling count sit within the self-build limits, and the applicants can evidence entries on the authority's self-build register. The exemption applies and no gain plan is needed. Change one fact, so that two of the four homes are for open market sale, and the exemption falls away for the whole scheme, bringing in a metric assessment on modified grassland with a mature hedge along one boundary. The figures are illustrative.

Keeping up with the changes

The regime has moved several times since 2024, through amendments to the regulations, revised metric versions and updated guidance on small sites. Government has also consulted on changes to how the requirement applies to minor development, so anyone reading an older article should check the current position on gov.uk before relying on it.

The same caution applies to policy citations, since the Framework itself has been re-issued twice in two years. Our note on citing the Framework after the move to policy codes covers how to reference it safely, and the planning law timeline is the place to follow reform as it lands.

Enter your postcode on PlanScope to check whether a site is likely to fall within the gain requirement and what the supporting evidence base looks like.

This is general guidance, not legal advice. Check the position with your local planning authority or a qualified professional before relying on it. PlanScope provides AI-assisted draft reports for planning applications. Reports should be reviewed before submission. We do not guarantee planning approval. For specialist technical reports, qualified professional input may be required.