Biodiversity Net Gain Exemptions
Not all development in England is subject to the mandatory Biodiversity Net Gain requirement. A number of exemptions apply, and the framework changed significantly on 6 August 2026 — most notably with the introduction of a new area-based exemption for smaller sites.
This page sets out the current exemptions, what changed, and what developers and planners need to establish before assuming a site falls outside BNG.
Last updated: July 2026.
What Changed on 6 August 2026
The Biodiversity Gain (Town and Country Planning) (Amendments and Transitional Provisions) (England) Regulations 2026 introduced four changes, applying to planning applications made on or after 6 August 2026.
Applications made before that date continue under the previous arrangements.
- A new exemption for sites of 0.2 hectares or less
- A new exemption for temporary development permitted for five years or less
- Removal of the self-build and custom-build exemption
- The biodiversity gain hierarchy relaxed for minor development, so registered off-site gains now sit on an equal footing with on-site creation
The Priority Habitat Condition — Read This First
Both new exemptions carry a condition that is easy to miss and expensive to get wrong.
Neither the 0.2 hectare exemption nor the temporary development exemption applies where the development would negatively affect an on-site priority habitat.
That means site area alone does not determine exemption. A development of 0.15 hectares is not exempt if it would harm priority habitat present on the site.
Priority habitats include a range of woodland, grassland, hedgerow and wetland types listed under section 41 of the Natural Environment and Rural Communities Act 2006. Establishing whether any is present requires ecological assessment — it is not something that can be determined from a site plan or an assumption that a small site cannot contain anything significant.
Where trees, woodland or hedgerows are present, that assessment should happen before the exemption is relied on.
The 0.2 Hectare Exemption
Development is exempt from mandatory BNG where the area within the planning application red line boundary is no more than 0.2 hectares — 2,000 square metres — provided no on-site priority habitat is negatively affected.
The threshold is based on the development site area, not the area of habitat being removed. That distinction is the one most commonly misread. A site of 0.19 hectares qualifies regardless of how much habitat it contains; a site of 0.21 hectares does not, however little habitat is affected.
The exemption applies only to applications made on or after 6 August 2026 and is not retrospective.
Current BNG Exemptions
The following are exempt from the mandatory BNG requirement:
- Sites of 0.2 hectares or less — from 6 August 2026, subject to the priority habitat condition
- Temporary development — permission granted for five years or less, requiring removal and reinstatement of the land within that period, subject to the priority habitat condition
- Householder applications — works to your own home, including extensions, outbuildings and alterations
- Biodiversity gain sites — development on a registered biodiversity gain site itself
- De minimis — development affecting less than 25 square metres of on-site habitat, or less than 5 metres of linear habitat such as hedgerow
- Development not subject to the biodiversity gain condition — certain permitted development and applications that do not trigger the requirement
- High Speed 2 — covered by separate arrangements
The self-build and custom-build exemption, which previously covered schemes of up to nine dwellings on sites of 0.5 hectares or less, no longer applies to applications made on or after 6 August 2026. Many single plots will fall within the new 0.2 hectare exemption instead, but larger self-build schemes must now deliver 10% BNG like any other development.
Still to Come
Nationally Significant Infrastructure Projects are expected to become subject to mandatory BNG from 2 November 2026, covering major transport, energy and water schemes.
A consultation on a potential exemption for residential development on previously developed land closed on 10 June 2026, with the outcome expected in due course.
Exempt Does Not Mean No Tree Survey
This is the most common misunderstanding following the August changes, and it is worth being clear about.
An exemption from mandatory BNG removes the requirement to deliver a 10% biodiversity gain. It removes nothing else.
The National Planning Policy Framework still requires development to avoid harm to biodiversity where possible. Local planning authorities may still request ecological information. And where trees are present on or adjacent to the site, a BS5837 arboricultural survey remains a validation requirement in its own right — a great many schemes that are now BNG-exempt still need one.
Tree Preservation Orders, conservation area protection and the six-week notice requirement are also entirely unaffected by BNG status. See our guidance on protected trees.
How Trees and Hedgerows Affect BNG
Even where a development is subject to BNG, arboricultural input affects the outcome considerably.
Trees and hedgerows are measured as habitat features within the statutory biodiversity metric and contribute biodiversity units to the site baseline. Retaining existing trees and hedgerows in good condition preserves those baseline units and reduces the net gain that must be delivered elsewhere — which is frequently cheaper than removing them and compensating afterwards.
Urban Tree Management provides the arboricultural survey data the ecologist uses to calculate the baseline, and supports the tree and woodland planting element of BNG delivery. The metric assessment itself is carried out by a qualified ecologist.
For the wider framework, see understanding biodiversity net gain.
Is My Development Exempt?
Whether your development is exempt depends on the site area within the red line boundary, the type of development, the date of the application, and whether priority habitat is present.
The 0.2 hectare threshold means many smaller extension, infill and minor development sites now fall outside mandatory BNG. But exemption cannot be assumed from site size alone, and other requirements continue to apply regardless.
If you are unsure, we can advise on the arboricultural position and, where a full metric assessment or priority habitat determination is needed, refer you to a qualified ecologist.
Frequently Asked Questions
What is the new 0.2 hectare BNG exemption?
From 6 August 2026, planning applications for developments where the red line boundary is 0.2 hectares or less are exempt from mandatory BNG, provided no on-site priority habitat is negatively affected. It applies only to applications made on or after that date.
Is my small site automatically exempt?
No. The exemption does not apply where the development would negatively affect an on-site priority habitat, regardless of how small the site is. That needs establishing rather than assuming.
I applied before 6 August 2026. Do the new exemptions apply?
No. The changes are not retrospective. Applications made before that date continue to be assessed under the previous rules.
My development is exempt — do I still need a tree survey?
Very possibly. BNG exemption does not remove other requirements. Where trees are present on or near the site, a BS5837 survey remains a validation requirement in its own right, and TPO and conservation area protections are entirely unaffected.
Is self-build still exempt?
Not as a category. The separate self-build and custom-build exemption was removed for applications made on or after 6 August 2026. Many single plots will fall within the new 0.2 hectare exemption instead, but larger schemes must now deliver 10% BNG.
Biodiversity Net Gain — Arboricultural Support Across the North West
Urban Tree Management provides the tree and hedgerow survey data that underpins BNG baseline calculations, and supports the tree and woodland planting element of delivery — working alongside your ecologist.
Get in contact with our highly experienced and personable team of arboricultural consultants today, to discuss your requirements and to obtain your zero obligation quotation.
