img(height="1" width="1" style="display:none" src="")

What legislative areas do architects need to know more about on biodiversity net gain?

Neal Morris

Learn more as the November deadline for implementing a minimum 10% uplift approaches

The legislative framework that will apply to uplift biodiversity net gain is less well known.
The legislative framework that will apply to uplift biodiversity net gain is less well known. Credit: iStock Photo

Under the UK government’s 25-year Environment Plan, all new development must provide a biodiversity uplift of a minimum of 10%. Implementation is just months away.

From November, developers will have to carry out a biodiversity assessment of their site and submit a Biodiversity Net Gain Plan for delivering the uplift alongside their planning application.

For small sites, uplift plans will not be required until April 2024 on the government’s current timetable. Small sites are defined in two ways: residential (where the number of dwellings is between one and nine on a site of less than one hectare, or where the number of dwellings is not known on a site area of less than 0.5 hectares); and non-residential (where the floor space is less than 1,000 square metres or where the site area is less than one hectare). The full definition is provided by Defra.

Most architects will be aware that the core tool for calculating how development will change the biodiversity value of a site is the Biodiversity Metric, which has been available with a user guide since last summer (there is a separate small sites metric and user guide). The new currency for uplift will be ‘biodiversity units’.

Less well understood is the legislative framework that will apply to uplift, such as the biodiversity hierarchies that must be applied at site level, the offsetting options for sites where uplift is simply not achievable, and the wider Nature Recovery Strategies that local uplift efforts are supposed to plug into.

How to apply a mitigation hierarchy

Biodiversity Net Gain is not a matter of adding 10% or more to what is already there. Architects will have to apply a mitigation hierarchy to the process, which is enshrined in the National Planning Policy Framework.

The hierarchy calls for a sequential approach:

Avoid: Avoiding biodiversity loss is the most effective way of reducing potential impacts, and it requires biodiversity to be considered at early design stages. The most effective avoidance mechanisms will be achieved through pre-application engagement with an ecologist and/or local planning authority and early identification of any surveys that need to be undertaken.

Minimise: Measurements should be taken to reduce the duration, intensity and/or extent of impacts to biodiversity. Where avoidance is not feasible, it is seen as essential to minimise potential negative impacts by modifying the project design and strategy to the fullest extent possible.

Mitigate: All non-avoidable ecological damage must be adequately replaced/mitigated with the guidance and expertise of a trained ecologist. Planning applicants will have to provide a strong evidence-case to demonstrate why avoidance and minimisation strategies were not viable.

Offset: Offsetting or compensation for adverse and unavoidable impacts is seen as the last resort. Biodiversity net gain offsetting mechanisms could include creation or enhancement of off-site habitats, purchasing biodiversity units on the market or purchasing statutory credits.

Kerri McCarton, Project Coordinator for Resilience and Nature at UKGBC, advises that the 10% biodiversity uplift should always be regarded as a minimum baseline, not a target. She adds that design proposals should aim to go beyond the number, and consider biodiversity holistically to achieve the full range of economic and social benefits. Under current guidance, projects that rely solely on offsetting without providing strong evidence of why other elements of the hierarchy could not be used risk refusal by planners.

Planning applicants will need to submit a Biodiversity Net Gain Plan that explains how the mitigation hierarchy has been addressed as well as the Biodiversity Metric assessment. Defra is still testing templates for these plans, says UKGBC Policy Advisor Philip Box, and further guidance is expected to appear before the November deadline.

Using the Proximity Principle for on-site and off-site measures

If biodiversity net gain cannot be achieved on site, then the gain must be achieved by following the proximity principle. Off-site opportunities must be identified with priority given to local enhancements, while statutory credits may be purchased only as a final option.

The Biodiversity Metric penalises net gain proposals as distances of locations increase from the development site, and conversely applies a multiplier where proposals align with local nature priorities, such as those identified in Local Nature Recovery Strategies or local biodiversity plans.

Information on off-site and on-site measures will need to be included in the core BNG information submitted with the planning application.

McCarton says when net gain is onsite, architects will need to plan ahead, because gains should be secured for delivery within 12 months of the development being commenced. There should be a clear timeline set out for delivery of the biodiversity net gain.

Proximity deals are seen as a great opportunity for the sourcing of investment in local priority projects, where the pooling of contributions will benefit from economies of scale, she adds.

How to identify local nature recovery strategies

Architects must identify opportunities to enhance local nature recovery sites through consultation with local authorities. They can examine local habitat maps and identify how strategies can enhance sites such as local nature reserves, wildlife sites and irreplaceable habitats.

The Environment Act mandates the creation of spatial plans to be known as Local Nature Recovery Strategies (LNRS), which will prioritise areas for specific actions. The Strategies will set out biodiversity priorities within strategy areas and describe opportunities for biodiversity recovery or enhancement.

The government has published statutory guidance on what an LNRS should contain, though further guidance on how the strategies should be reflected in Local Plans is still awaited.

Some local authorities have done the groundwork for their strategies and Defra has funded five LNRS pilots, though it remains to be seen what sort of formal LNRS coverage will be in place by November. Some areas, such as Greater Manchester, have already started drawing up lists of priority sites that developers can consult, says Box.

To encourage off-site enhancements in the areas of greatest benefit, the Biodiversity Metric suggests a 15% uplift in units generated when actions take place in locations proposed by the LNRS.

What can Biodiversity Net Gain's contribution be to existing targets?

Biodiversity Net Gain delivery should be part of a strategic approach aligned with key targets and priorities set out in the Environment Act. These priorities are underpinned by key data sources.

These include the data indicators being developed to monitor progress against the government’s 25 Year Environmental Plan.

With the countdown to November now underway, UKGBC has launched a series of essential factsheets that look beyond the metrics, alongside a specific definitions list.

UKGBC plans to deliver further resources to support the built environment sector’s journey to understanding an implementing biodiversity net gain in the future.

Thanks to Kerri McCarton, Project Coordinator: Resilience and Nature, UKGBC; Philip Box, Policy Advisor: Nature & Resilience, UKGBC.

RIBA Core curriculum topic: Sustainable architecture.

As part of the flexible RIBA CPD programme, professional features count as microlearning. See further information on the updated RIBA CPD core curriculum and on fulfilling your CPD requirements as an RIBA Chartered Member.



Launching our new summer series on inventive house extensions, Artefact co-founder Benedetta Rogers talks about a new wing to a detached home in Epsom, informed by the clients’ Caribbean heritage

Artefact on its new wing for a detached home in Epsom that spurns open-plan living spaces

The founding partner of Gustafson Porter + Bowman explains why she finds landscape architecture so fascinating, how it is great for who she is and why her mantra is ‘the sky is mine’

Why the landscape architect says ‘the sky is mine’

Three borough councils are expected to pipeline their projects through a new agreement designed to build engagement between the capital's public sector clients and a diverse range of architects

Three boroughs are expected to pipeline their projects through new agreement, which launches in May 2025

Howells’ new restaurant building has turned a run-down services area into a leisure asset and made a National Trust house into a local destination

From down-at-heel services area to leisure asset

RIBA-backed platform developed by Grimshaw-led team provides comprehensive guidance and management tools to help cut carbon throughout the building process

Grimshaw-led team's guidance and management tools cover the entire building process