Biodiversity net gain became mandatory for most development in England in February 2024. The principle is simple enough to state: a development has to leave the natural environment measurably better than it found it, by at least 10%, either on the site itself or by buying units elsewhere.
On 6 August 2026 the rules changed. Three things happened that day, and they did not all point the same way.
The three biodiversity net gain changes of 6 August 2026.
The first change is the one that was reported. From 6 August 2026, biodiversity net gain does not apply to a planning application where the site area inside the red line boundary is 0.2 hectares or below. The guidance states it without qualification.
The second change was reported much less. A new exemption now applies to temporary developments, meaning those granted permission for five years or less.
The third change was barely reported at all, and it is the one worth the attention. The exemption for self-build and custom build housing has ended. It now applies only to applications made before 6 August 2026. Anyone applying to build their own home on or after that date is inside the biodiversity net gain regime for the first time.
So the day was not a relaxation. It was a swap.
Two exemptions were created and one was taken away, on the same morning, and the one taken away belonged to the only group of housebuilders the government has spent a decade trying to encourage.— The Editor · Ground Level, August 2026
How big 0.2 hectares is, measured in homes.
Thresholds expressed in hectares are hard to picture, and the picture matters here.
0.2 hectares is 2,000 square metres. In older units it is a little under half an acre. As a rough rectangle it is about 45 metres by 45.
The useful way to read it is in homes. At around 35 dwellings to the hectare, which is an unremarkable density for an edge of village or suburban scheme, 0.2 hectares holds about seven homes. At 50 to the hectare, a denser urban layout, it holds about ten.
That lands the new exemption almost exactly at the point where a development stops being minor and becomes major. In England, major residential development starts at ten dwellings. So the effect of the change is that a very large share of the schemes below that line now have no biodiversity obligation at all.
There is a reasonable case for it, and it should be put. The cost of a biodiversity assessment does not scale down neatly. A metric calculation, an ecologist's survey and a 30 year management plan cost broadly the same on a four home site as on a forty home site, and on the small scheme that fixed cost is a much larger share of the project. The government's own case for the change is that the administrative burden on small developments was disproportionate to the ecological benefit it produced.
The counter-case is equally straightforward. Small sites are where hedgerows, mature trees and rough margins actually sit in a village. A field of 40 homes is assessed, mitigated and monitored. Seven homes on the paddock behind the pub is now, for these purposes, invisible.
Why self-build lost its biodiversity net gain exemption.
Self-build and custom build housing has been an object of government policy for over a decade. Councils have been required since 2016 to keep a register of people who want to build their own home, and to grant enough permissions to meet the demand on that register. The stated purpose has been consistent across administrations: diversify housing supply away from a market dominated by a small number of volume housebuilders, and give people a route to a home that does not involve buying one from a plc.
Self-build was exempted from biodiversity net gain when the regime began. From 6 August 2026 it is not.
An individual building one house is now in the same regime as a developer building forty, minus the professional team. They will need the metric, the baseline habitat assessment and, if the gain cannot be delivered on the plot, the purchase of off-site units and a legal agreement securing them for 30 years.
The 0.2 hectare exemption will rescue many of them, because a single house on a single plot is usually well inside that. But not all self-build plots are small, and the two changes do not cancel out. A self-builder on a half hectare plot with a paddock has gained nothing on 6 August and lost something.
The reason this is worth naming is that it is the same shape as a pattern this publication keeps finding. A policy is introduced to encourage something. A cost is later attached to it, quietly, in an amendment to something else. Nobody announces that the encouragement has been withdrawn, because formally it has not been. The register still exists. The duty on councils still exists. What has changed is the price of using it.
What biodiversity net gain still requires.
It is worth being clear about the limits of all this, because there is a version of this story that overstates it.
Everything above concerns England, and it concerns the exemption list. The core requirement is untouched. A major development still has to deliver a 10% gain, still has to use the statutory metric, and still has to secure any off-site units for 30 years. The de minimis rule, which lets out developments affecting less than 25 square metres of habitat or 5 metres of linear habitat such as hedgerow, is unchanged and predates this.
Nor is biodiversity net gain the only ecological constraint on a small site. Protected species law is entirely separate and applies regardless of scheme size. A bat roost, a great crested newt pond or an active badger sett is a legal obstacle whether or not the site is above 0.2 hectares, and the exemption does nothing to change that.
The distinction matters. Biodiversity net gain is about the general habitat value of a site and the requirement to improve it. Species licensing is about specific protected animals and the requirement not to harm them. Losing the first does not touch the second.
Environmental Delivery Plans and the Nature Restoration Fund.
There is a larger reorganisation of nature and planning underway, and these amendments sit inside it.
The Planning and Infrastructure Act 2025 creates Environmental Delivery Plans, funded by a levy paid into a Nature Restoration Fund. The idea is to replace site by site negotiation with pooled mitigation at a landscape scale, so that a developer pays into a fund and Natural England delivers the environmental outcome somewhere it will do more good. In December 2025 Natural England notified the Secretary of State of its intention to prepare 23 such plans, 16 of them addressing nutrient pollution. The government committed to consulting on the first of them during 2026.
Read alongside that, the direction of the August amendments is legible. Small sites are being taken out of a site by site regime at the same time as a pooled regime is being built. Whether the second arrives in a form that actually delivers is the question, and it is the same question this publication has raised about every pooled mechanism from the Community Infrastructure Levy onwards. Money is collected reliably. Delivery is harder to observe.
How to check whether an application near you is exempt.
If you sit on a parish or town council, or you comment on applications in your area, two things are now worth checking that were not worth checking a month ago.
First, the red line. The exemption is measured by the site area inside the application's red line boundary, not by the number of homes and not by the area actually built on. An applicant drawing a tight boundary around a plot is drawing the thing the threshold is measured against.
Second, the date. Applications made before 6 August 2026 sit under the old rules, including the self-build exemption. Applications made on or after it sit under the new ones. On a scheme that has been in preparation for months, which side of that line it falls on may not be obvious from the documents.
The exemption list is published and is a single page. It is the fastest way to establish whether an application near you has any biodiversity obligation at all.