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Start a conversationBiodiversity net gain, explained.
The ten per cent rule, who stopped being caught in August 2026, and what a shortfall costs.
Reviewed August 2026
The short answer
Biodiversity net gain is a legal requirement for most development in England to leave nature measurably better off, by at least 10 per cent, secured for 30 years. Since 6 August 2026 sites of 0.2 hectares or less are exempt, provided no priority habitat is affected.
In practice · Burton Green
Won in October, issued in February
The cost of leaving net gain late is easiest to see on a scheme where it was the last thing standing.
The order of work
01Test the siteWhether net gain applies at all, before anything is drawn.
02Design the gainWhat the layout can carry without losing a plot.
03Secure the shortfallThe off-site agreement, drafted alongside the application.
04Then the noticeConsent issues once the agreement completes.
Four homes on a back-land plot at Burton Green, near Kenilworth. A third of a hectare, hemmed in by neighbours, reached by a single narrow access. It drew a parish council objection and ten others, which took the decision out of officers' hands and sent it to Planning Committee.
The job
- Site
- A 0.36 hectare back-land plot at Burton Green, near Kenilworth
- Role
- Architect and planning agent, application run to committee
- Consent
- Warwick District Council ref W/24/0454, four homes
- Outcome
- Resolved at committee October 2025, issued February 2026
The committee granted it on 7 October 2025, upholding the officer recommendation. The decision notice was issued on 25 February 2026.
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Four and a half months sat between those two dates, and what sat in them was the section 106 agreement securing the off-site biodiversity net gain and the carbon offsetting. The permission was resolved in the autumn. It became a permission anyone could build on in the winter.
That gap is the argument for treating net gain as a design question rather than a paperwork one. It is not a condition to be discharged at leisure once consent is in hand. Here it was part of what made the consent issuable at all.
The plot measures 0.36 hectares. The exemption that arrived on 6 August 2026 stops at 0.2, so a site of this size and shape would still be caught today and the same agreement would still be needed. The threshold is closer to most back-land schemes than it sounds.
Net gain was not the only thing in that agreement. Carbon offsetting sat alongside it and the two were negotiated together. Where a scheme needs a legal agreement at all, it is worth knowing early what else will be loaded into it, because the agreement completes as one document or not at all.
The proof
Ecology, resolved in the consent.
Protected species · discharged
Ashlawn Road, Rugby
A countryside family home on the edge of Rugby. A protected bat roost in the existing building is where a good many programmes stall. The survey work and the mitigation went in with the application rather than after it, and the ecology condition was discharged twenty-three days early.
Rugby Borough Council · consented, condition discharged
Refusal ground · answered
Oakridge Lynch, Stroud
Nine homes in the Cotswolds, refused on eight grounds. One of them was ecology, the council being unsatisfied on great crested newts. The answer was evidence rather than redesign, an updated survey and a reading of what the data actually showed, and the appeal was allowed in October 2025.
Stroud District Council · allowed at appeal, October 2025
Habitat bank · 68 acres
Wood Farm, Everdon
Sixty-eight acres in Northamptonshire, managed as a habitat bank so that schemes which cannot deliver their gain on site can buy the units elsewhere. Dan Rickett, a director of the practice, owns it. Units are sold through a broker, and the bank has the flexibility to discount them.
Wood Farm Grounds Ltd · units available through a broker
Every planning application we make in our own name is a matter of public record on a council register, and ours reach more than 100 planning authorities across the UK.
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01 · Where you stand
First, check whether your site is caught
Net gain does not apply to everything, and what it misses changed on 6 August 2026. Checking is a desk exercise, and it is worth doing before anything is drawn.
Three tests take a site out of scope on size. A development of 0.2 hectares or less, measured to the red line. A development touching less than twenty-five square metres of habitat, or five metres of hedgerow. And a temporary permission of five years or less.
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All three carry the same override, and it is the one that catches people out. None of them applies if the development impacts a priority habitat on site. A small site with priority habitat on it is caught however small it is, so the habitat question has to be answered before the area question is worth asking.
Householder applications are out entirely, and so are permitted development rights and urgent Crown development. Off-site gain sites are exempt themselves, which makes sense once you see that their whole purpose is to carry somebody else's obligation.
The area test is measured to the red line, which means the boundary drawn on the application decides whether the scheme is in scope. That is worth thinking about before the plan is drawn rather than after, because a boundary drawn loosely can put a scheme into a regime it did not need to enter.
02 · The routes
Four routes to the ten per cent
The gain can come from four places and they are not equally priced. On anything below major development the first three now rank equally, which is new since August 2026.
Route 01
Enhance what is there
The cheapest units are the ones already on the site. Improving the condition of existing grassland, hedgerow or woodland scores against the same metric as making something new, and costs a fraction as much, because the habitat is already established.
Where it fails: condition has to be evidenced by survey, not assumed from a site walk.
Route 02
Create habitat on site
New planting, ponds, meadow, green roofs. This is where layout and net gain start arguing with each other, because land given to habitat is land not given to homes. Running the metric early is what stops that argument happening after the layout is fixed.
Where it fails: a scheme that reaches planning before the metric is run usually loses a plot.
Route 03
Buy registered units
Where the site cannot carry the whole gain, the shortfall is bought in. Only units on the biodiversity gain sites register count towards it, and the land behind them has to be managed for thirty years under a legal agreement of its own.
Where it fails: the agreement takes time, and on a section 106 scheme it can hold the decision notice.
Route 04
Statutory credits
The government sells credits directly, as a deliberate last resort. They are available to any scheme that genuinely cannot find units, so nothing is ever truly blocked, but they are priced to make certain nobody reaches for them first.
Where it fails: it does not fail. It simply costs more than every other route, by design.
03 · The cost
What a shortfall actually costs
There is no published price for a biodiversity unit, because the off-site market is private and brokered. There is a published price for the alternative, and that is what makes the rest of it legible.
Statutory credits run from forty-two thousand pounds a credit at the lowest tier to six hundred and fifty thousand at the highest, with hedgerow and watercourse credits priced separately. Two credits are required for every one biodiversity unit. So the cheapest unit anyone can buy this way costs eighty-four thousand pounds.
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That figure is a ceiling rather than a price. The government set the credits high, in its own words to ensure they do not compete with the development of the private market, so any off-site quote worth having sits below it. Knowing where the ceiling is tells you whether a quote is reasonable.
The arithmetic that decides a feasibility is not the price per unit, it is the number of units. A site of tired grassland and a thin hedge starts from a low baseline and needs very little to clear ten per cent. A site carrying mature habitat starts high, and every unit of that baseline has to be replaced before the uplift even begins.
Which makes net gain a site-selection question before it is a design question. Two sites of the same size, in the same town, carrying the same number of homes, can arrive at very different net gain bills, and the difference is visible from a desk long before anyone commissions a layout.
Common questions
Net gain, answered
When did biodiversity net gain become mandatory?
12 February 2024 for major development, and 2 April 2024 for small sites.
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Applications made before those dates are not caught, and neither are variations of permissions that were never subject to it. Nationally significant infrastructure projects come into scope on 2 November 2026, the last major commencement still outstanding at the time of writing. The date that decides it is when the application was made, not when it was determined, which matters on anything that has sat in the system for a while.
How is biodiversity net gain measured?
With the statutory biodiversity metric, which converts habitats into biodiversity units.
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The metric scores each parcel of habitat by type, distinctiveness, condition and strategic significance, then does the same for what is proposed. The difference between the two is the gain. Because condition carries real weight, an accurate baseline survey is worth more than an optimistic one in either direction: a baseline pitched too high makes the ten per cent harder to reach, and one pitched too low will not survive scrutiny.
What is a biodiversity gain plan?
The document showing how the gain will be delivered. It has to be approved before development starts.
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The requirement arrives as a condition on the permission, and the law treats that condition as attached whether or not the authority writes it in. The plan sets out the baseline, the post-development value, what is being done on site, what is being bought off site with the register references, and any credits. Because it is pre-commencement, it sits between consent and starting work, which is exactly where an unresolved shortfall becomes a delay.
What is a habitat bank?
Land managed to generate biodiversity units that other people's developments can buy.
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The land goes under a legal agreement to be managed for at least thirty years, the gain is calculated, and the site is entered on the biodiversity gain sites register with its own reference. Only registered sites produce units that count. A developer buys a number of units and cites that reference in the gain plan. The land itself stays with the bank, which is what lets it serve schemes that have no room of their own.
Can a self-build still claim the exemption?
Only where permission was granted before 6 August 2026. The exemption was removed on that date.
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The regulations that came into force on 6 August 2026 omit the self-build and custom build exemption entirely, with a transitional provision preserving it for applications made before then. A self-build scheme carried forward on the old assumption is worth re-checking, because it may now have to meet the ten per cent like anything else, or fall under the area test instead.
How does net gain interact with nutrient neutrality?
They are separate regimes, and satisfying one does nothing for the other.
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Net gain is a biodiversity uplift under the Environment Act. Nutrient and water neutrality are catchment-based constraints under the habitats regulations, and they can hold a consent until mitigation is secured. A site in an affected catchment has to resolve both, through different markets and different evidence. The order they are tackled in affects the programme, so both are worth testing at feasibility rather than discovering one after the other.
What happens after consent, and for how long?
The habitat has to be maintained for at least thirty years, secured by a legal agreement.
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That is a section 106 obligation or a conservation covenant, and it binds the land rather than whoever signed it. Monitoring and reporting are usually written into the same agreement. Thirty years is longer than most development companies hold a site, which is why the obligation attaches to the land, and why buyers and funders have started asking about it during diligence.
Written by
Rickett Architects
A RIBA Chartered practice, working since 1970, with more than 2,500 projects behind it. Our senior architects take projects from first survey through planning to completion, for private clients, developers and landowners across the Midlands and well beyond it.