If you are building your own home, a key exemption is about to disappear. From 31 July 2026, the exemption that let self-build and custom-build dwellings sidestep Biodiversity Net Gain (BNG) is being removed. After that date many self-builders will, for the first time, need to think about the 10% biodiversity uplift that already applies to most other development in England.
This article explains exactly what is changing, why, and — importantly — why most self-build plots will still avoid a full BNG assessment through a different route.
What is changing on 31 July 2026
BNG, introduced under the Environment Act 2021, requires most new development to deliver a measurable 10% net gain in biodiversity. When the regime began, self-build and custom-build housing had its own carve-out. The government has now confirmed that this self-build/custom-build exemption is being removed from 31 July 2026, as part of a wider package of BNG reforms first announced in April 2026 and refined through transitional guidance published in July 2026.
The reasoning is straightforward: the exemption was widely seen as open to abuse and hard to apply consistently. Removing it is part of a deliberate move away from development-type exemptions ("is this a self-build?") towards a cleaner, site-based approach ("how big is the site, and does it touch priority habitat?").
The 0.2 hectare exemption is the safety net
Here is the reassuring part for most self-builders. On roughly the same timetable, a new small-sites exemption applies to development on land of no more than 0.2 hectares, provided the works do not affect an on-site priority habitat. The great majority of self-build and custom-build plots are 0.2 hectares or smaller — so in practice most of them simply move from the old self-build exemption to the new area-based one.
In other words, for a typical single-plot self-build on a modest garden or infill site, the day-to-day position may not change much: you were exempt before, and you are likely still exempt after — just under a different rule. We explain that rule in detail in the 0.2 hectare BNG exemption. What changes is that the exemption now depends on site area and habitat, not on the fact that you are building for yourself.
Who is actually caught?
The self-builders who will be brought into BNG are those on larger plots — typically rural or edge-of-settlement sites above 0.2 hectares — or on smaller sites that contain or affect a priority habitat (such as species-rich grassland, hedgerows or established woodland). If that is you, a self-build project now needs to engage with BNG properly:
- A baseline habitat assessment using the statutory biodiversity metric, ideally before you finalise the layout.
- A route to 10% net gain — on-site enhancement first, then off-site units, with statutory credits as a last resort. Our guide to delivering 10% BNG on a small site sets out the practical order.
- A 30-year commitment to secure and maintain the habitat, usually through a planning condition or obligation.
Watch the transitional arrangements
Timing matters. The government has published transitional guidance clarifying how applications straddling the change should be treated, with the broader reform package coming into force in early August 2026. If your application is in the system now, or you are about to submit, the sensible step is to confirm with your local planning authority which rules apply to your specific application date — an exemption you assumed you had may hinge on a matter of days. This sits within the wider set of 2026 BNG changes reshaping the regime this year.
Why it belongs in your sustainability statement
BNG is one strand of the broader sustainability case a planning application must make, alongside water efficiency, energy and — where required — BREEAM. Even where a self-build qualifies for the small-sites exemption, a good sustainability statement should evidence that exemption clearly (site area, absence of priority habitat) rather than simply asserting it. Validation officers increasingly expect the exemption to be demonstrated, not assumed — a theme we return to across our sustainability guidance.
What self-builders should do now
- Measure your plot. Confirm whether it is at or under 0.2 hectares — that single figure decides which regime you fall under.
- Check for priority habitat. If any part of the site could be priority habitat, assume BNG may apply and get an ecologist involved early.
- Evidence the exemption. Put the site area and habitat position in writing in your sustainability statement.
- Mind the date. If you are close to submission, know whether your application lands before or after 31 July 2026.
How Fortress Associates can help
Fortress Associates produces automated sustainability statements for UK planning applications, covering biodiversity net gain, water efficiency (the 110 l/p/d Part G calculator), urban greening and BREEAM where required. The report is free and ready in minutes, and helps you set out your BNG position — whether that is a route to 10% net gain or a clearly evidenced small-sites exemption. If you are planning a self-build affected by these changes, get in touch or see our full services.
Sources & further reading
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