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What do architects need to know about biodiversity net gain legislation?

Neal Morris

Learn more about the new biodiversity net gain regime and what architects can expect

The new biodiversity net gain regime is now live
The new biodiversity net gain regime is now live Credit: iStock Photo

It has been twice delayed, but biodiversity net gain (BNG) finally becomes mandatory for major developments from 12 February 2024 and will then be applied to small sites from 2 April 2024. (A small site is defined here among other things, as a residential development where the number of dwellings is between one and nine, or if this is unknown, the site area is less than 0.5 hectares.)

The passing of secondary legislation is seen as a hugely positive step in combating the biodiversity crisis. The Environment Bank says that during five decades, the UK has lost 60% of its biodiversity. This shocking statistic affects everyone, from humans to animals, but this legislation makes architects who work with developers and the built environment as a whole a central part in the restoration.

Enabling legislation has been in place for three years, but it was only at the close of last year (2023) that a handful of statutory instruments were laid before Parliament to deal with some of the technical nuts-and-bolts of the new BNG regime.

So what’s new and what can architects who work in this area expect?

How does biodiversity work within existing planning procedures?

Among other things, the recent legislation stipulates set fines (£5,000) for submitting incorrect data on existing biodiversity, allowing a site register of land to be set up for the sale of offsite credits, and clarifying the habitats that are to be considered ‘irreplaceable’.

There is now draft planning guidance on how the BNG process will work within existing planning application procedures.

BNG will be dealt with as a post-permission matter: once planning permission has been granted, a Biodiversity Gain Plan must be submitted and approved prior to the commencement of development. This will confirm how the biodiversity gain objective of at least 10% will be met for the development within approved plans, or whether offsite gains have been registered and allocated or biodiversity credits purchased.

Ben Stansfield, Partner and environmental law specialist at Gowling WLG, says the secondary legislation was a fairly predictable set of regulations that largely confirmed what the industry was expecting.

We also now have a definite and confirmed biodiversity hierarchy, which architects will need to apply to development sites. This is headed by avoiding adverse effects of the development on onsite habitat with a habitat distinctiveness score (applied in the Biodiversity Metric) equal to, or higher than ‘six’. Where adverse effects cannot be avoided, effects should be mitigated.

If you can't do that in relation to the onsite impact, then you’ve got to try and enhance existing habitats, and Stansfield suggests this is likely to be key to BNG on the majority of sites. Only where this is not feasible will developers be able to opt for the purchase of offsite gains or, as a last resort, BNG credits.

A lot of developers were hoping they would have the automatic option of purchasing offsite gains, he adds. But this has not happened and he expects that planners will be looking for a demonstration that enhancement was properly considered before being found to be genuinely not feasible.

‘I think planners will expect to see a paper trail with arguments as to why onsite solutions are not appropriate,’ he suggests.

Read more about tips to comply with BNG planning requirements

Why checking planning policies is important

The industry was put on notice that BNG was coming and biodiversity baselines are supposed to be set from this time. Planners – not unreasonably - may choose to investigate sites if they suspect developers have been trying to ‘game the system’.

Stansfield also recommends that architects should check the BNG policy of individual planning authorities. The 10% BNG uplift is a minimum, and he is already aware of 15-20 local authorities that are adopting or considering 15% or 20% uplifts or even higher.

With all that being said, the first thing any architect must do once they have their red-line demarcated site, of course, is to assemble reliable biodiversity data on what types of habitats are there and populate the government’s statutory Biodiversity Metric (this may be led by a specialist consultant, depending on project scope). Most larger practices will be familiar with the metric as various trial versions have been around for several years hosted by Natural England.

Except for small sites (nine dwellings or fewer), where use of the small sites metric will be allowed, the metric tool should be used by an ecologist or similarly competent person. Where architects are taking care of the planning application as well as the design, they will need to submit the completed statutory metric, Stansfield points out, and may not have the in-house skills.

The government has said that it expects the local planning authority to review submitted calculations and to reject them if they do not believe they have been provided by a competent person.

Read more about boosting your site's biodiversity net gain

Biodiversity net gain and habitat management

Stansfield adds that while the new legislation is a hugely positive and important development for the built environment, there may be bumps in the road during the initial period of transition. There could be, he suggests, delays in gaining permission especially when it comes to the management and stewardship requirements for biodiversity assets beyond construction.

Any developer who has to deliver significant on-site biodiversity enhancement will have to submit a habitat management and monitoring plan (HMMP), which must set out who is responsible for 30-years of management of the assets.

Management of a site where there is a relatively simple habitant enhancement is likely to be covered by planning conditions, which Stansfield suggests are likely to look like beefed-up versions of conditions already applied to landscaping assets. Anything more significant is going to need a Section 106 agreement.

For offsite solutions there will be the same 30-year management requirement, requiring either a Section 106 agreement or a ‘conservation covenant’ with a designated body. However, apart from Natural England (which as keeper of the offsite land register is declining to take on covenants), none of these designated bodies yet exist.

This means that for management of any significant enhancements, Section 106 will initially be the only game in town.

'We already know that Section 106 agreements take time to get resolved and can be a source of delay,' he says, 'but these biodiversity agreements will be quite different and will have new types of obligations that legal departments will be gearing up for.'

However, despite the potential for some initial bumps in the road, the introduction of the new regime and its subsequent requirements is a hugely positive development.  

‘Nature is the new carbon,’ posits Stansfield. ‘Everyone is taking it seriously. I think planning officers will not just be looking at BNG, but will see it as an opportunity to incorporate nature into design and really make it a feature of developments.’

Thanks to Ben Stansfield, Partner, Gowling WLG.

This is a Professional Feature edited by the RIBA Practice team. Send us your feedback and ideas

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