Biodiversity Net Gain in 2026 – What Developers Need to Know About the Next Wave of Changes
by Joe Bradley
When I wrote about Biodiversity Net Gain (BNG) ahead of its introduction, the industry was understandably focused on one question: How do we comply?
Two years on, most planning professionals, architects and developers have become familiar with the fundamentals. BNG has become another established part of the planning process, much like drainage, highways or heritage considerations.
However, 2026 is shaping up to be another significant year for the legislation.
Rather than changing the core principle of delivering a minimum 10% biodiversity net gain, Government is introducing a series of reforms intended to reduce complexity for smaller developments whilst maintaining environmental outcomes.
So, what is changing - and who should be paying attention?
Key Date: Before 31 July 2026
The Government has confirmed that secondary legislation is expected before 31 July 2026, introducing a number of important amendments following its review of BNG implementation.
The headline changes include:
A new 0.2 hectare area-based exemption for qualifying developments.
Removal of the current self-build and custom build exemption.
Temporary planning permissions of up to five years becoming exempt.
Changes to the Biodiversity Gain Hierarchy for minor developments, making off-site delivery a more practical option.
Continued development of a digital Biodiversity Metric, replacing the current Excel-based process in the future.
What Does This Mean for Small Developers?
For many small developers, these proposals should reduce both cost and administrative burden.
One of the biggest criticisms of the original legislation was that relatively modest developments often faced the same procedural requirements as much larger schemes. The proposed 0.2 hectare exemption is intended to create a more proportionate system where ecological risk is relatively low.
However, there is an important caveat.
The removal of the existing self-build exemption means that eligibility will increasingly depend on the size and characteristics of the site rather than the identity of the applicant. Some self-build projects that were previously exempt may now fall within the BNG regime if they exceed the new thresholds, while many smaller plots will remain exempt because they fall below the proposed area limit.
Medium-Sized Developers
Developers delivering schemes beyond the proposed exemption threshold should not expect significant relaxation of requirements.
The Government has made it clear that BNG remains a central part of planning policy. The emphasis is instead on simplifying the process rather than weakening biodiversity objectives.
For these projects, the advice remains largely unchanged:
Engage an ecologist at the earliest opportunity.
Understand the site's baseline biodiversity before fixing layouts.
Consider biodiversity alongside viability from the outset rather than treating it as a planning condition to resolve later.
In practice, the earlier BNG informs the design process, the cheaper compliance generally becomes.
Major Developers
For larger residential and commercial developments, very little changes.
The 10% mandatory biodiversity gain remains in place, as does the expectation that gains are secured for a minimum of 30 years through appropriate legal agreements.
Large developers should instead keep an eye on forthcoming updates to the Biodiversity Metric and associated guidance, which are intended to improve consistency, particularly around urban habitats, open mosaic habitat and spatial risk assessments.
Nationally Significant Infrastructure Projects
Perhaps the biggest date for the infrastructure sector is 2 November 2026.
From this date, Biodiversity Net Gain will become mandatory for Nationally Significant Infrastructure Projects (NSIPs), bringing major transport, energy and infrastructure schemes into the BNG framework under their own arrangements.
Although the detailed implementation differs from standard planning applications, the direction of travel is clear: biodiversity enhancement is becoming embedded across virtually every scale of development.
My Advice Hasn't Changed
When BNG was introduced, I argued that the biggest mistake developers could make was treating biodiversity as something to deal with once the architectural design had been completed.
That remains true today.
In fact, as the legislation matures, the projects that perform best are increasingly those where architects, ecologists and planning consultants collaborate from the very beginning.
A simple adjustment to a building footprint, retaining an existing hedgerow, or protecting higher value habitats early in the design process can often save considerably more time and money than relying on expensive off-site biodiversity units later.
BNG is no longer "new" legislation. It is becoming a standard design constraint -mand, when embraced early, an opportunity to create developments that are both commercially viable and environmentally resilient.
As with many aspects of planning, those who plan ahead are likely to find compliance significantly easier than those trying to retrofit solutions at the end of the process.
