When to Use Off-Site Biodiversity Net Gain (BNG)
Off-site BNG explained for developers: when it's needed, the signs your site can't reach 10% on-site, and what to do after a biodiversity unit shortfall.
James Porter
8/12/202610 min read
When to Use Off-Site Biodiversity Net Gain (BNG)
Your ecologist has run the metric, and the numbers don't add up. The site can't reach a 10% biodiversity gain inside its red line, and the planning condition still needs discharging. That's the moment most developers first look seriously at off-site BNG.
Off-site biodiversity net gain is used when a development can't deliver its full 10% gain within its own boundary. Instead of creating all the habitat on-site, the developer secures biodiversity units from land elsewhere, usually a registered habitat bank, to make up the shortfall. Under the biodiversity gain hierarchy, it sits after on-site delivery and before statutory biodiversity credits, which are the last resort.
What is off-site biodiversity net gain?
Off-site biodiversity net gain is habitat created or improved away from the development site, then counted towards the scheme's 10% gain. The developer doesn't build the habitat themselves. They buy biodiversity units from a landowner or habitat bank that has already created, or committed to create, habitat on registered land.
Those units are recorded on the government's Biodiversity Gain Sites Register and allocated to a specific development, so the same habitat can't be sold twice. Whatever is created has to be secured and managed for at least 30 years, usually through a Section 106 agreement or a conservation covenant, with the long-term management arrangements sitting with the habitat provider.
A habitat bank is a land set aside for this purpose. A landowner creates or restores habitat such as grassland, woodland or wetland, registers it, and sells the resulting units to developers who need them. For developers, this can transform a complex on-site delivery challenge into a simple off-site procurement process, while the long-term habitat management is undertaken by specialist providers.
Why on-site BNG isn't always enough
On-site delivery is the default. The biodiversity gain hierarchy asks developers to create or enhance habitat inside the development boundary first, and off-site units come in only where the site can't get there on its own.
The trouble is that plenty of sites can't. The land that makes a scheme viable, the plots, roads, parking, drainage and usable open space, is the same land you'd need for habitat. On a tight site, every square metre given to a wildflower meadow is a square metre taken from something the scheme depends on.
A few common limits push developments off-site:
Not enough room. Urban infill, industrial units and dense residential schemes rarely have space for meaningful habitat once the buildings, access and parking are laid out.
Competing priorities. Affordable housing numbers, adoptable road widths, sustainable drainage and site access usually win the argument for space over new habitat.
The wrong ground. Sealed, contaminated or heavily disturbed land, common on brownfield sites, is hard to turn into high-value habitat.
Habitat mismatch. If a scheme removes a high-distinctiveness habitat, the Statutory Biodiversity Metric expects like-for-like or better. Recreating that quality on a small, built-up site often isn't realistic.
The timing point. On-site habitat is scored partly on how long it takes to reach target condition, so newly planted areas count for less at first than established habitat elsewhere. A registered habitat bank that's already in the ground can deliver the same gain without that wait.
Note - the rules are shifting in 2026
From 6 August 2026, minor developments that aren't otherwise exempt can weigh on-site and off-site options together, rather than having to exhaust on-site first. A separate 0.2-hectare exemption from August 2026 takes many of the smallest sites out of BNG altogether, and a brownfield residential exemption is under consultation. Thresholds and dates are still moving, so check the current position on GOV.UK for your specific scheme.
When should you use off-site BNG?
Use off-site BNG when your site can't realistically deliver the full 10% gain within its boundary and your ecologist's metric assessment confirms a shortfall. In practice, that's most schemes on constrained, built-up or brownfield land.
Signs your development may need off-site BNG
The Statutory Biodiversity Metric shows a biodiversity unit shortfall once the on-site design is set
The site is small, urban or tightly constrained
Parking, drainage, access or affordable housing take the space habitat would need
The site is brownfield, sealed or contaminated
You're removing a high-distinctiveness habitat that can't be recreated on-site
Your ecologist has recommended off-site delivery
Constrained urban and infill sites
On a small urban plot, the building footprint, access and parking often leave almost nothing for habitat. Even with green roofs and street trees, an infill scheme rarely creates enough units on-site to reach 10%. Off-site units usually cover most or all of the requirement. What to weigh: how few units you can realistically create on-site, and how many you'll need to buy.
Brownfield and redevelopment sites
Brownfield land is a mixed picture. Some previously developed sites carry surprisingly high baseline value from scrub, open mosaic habitat or self-seeded vegetation, which raises the gain you then have to deliver. Others are sealed and hard to plant well. Either way, recreating quality habitat on-site is often slow and uncertain, which pushes the gain off-site.
Commercial, industrial and logistics schemes
Warehousing, trade counters and industrial units are built to maximise floorspace and yard, so most of the plot becomes hardstanding and circulation. There's little soft landscaping in the design, and less still that scores well on the metric. These schemes almost always look off-site for the bulk of their units.
Note: securing units early, because larger commercial schemes can need a lot of them.
Residential schemes with limited green space
A housing layout might include some public open space, but amenity grassland and ornamental planting score low. Residential gardens score lower still. Unless the design builds in genuine, well-managed habitat, the on-site gain can fall short of 10%. Many residential schemes deliver part of the gain on-site and buy the balance off-site.
Loss of high-distinctiveness habitat
If development removes a high-distinctiveness habitat, such as species-rich grassland or certain high-value woodland habitats, the metric's trading rules require you to replace it with the same broad habitat type or a better one. Recreating that on a small site, at the right quality, usually isn't feasible. Off-site delivery through a habitat bank that already holds the right habitat type is often the only credible route. (Irreplaceable habitats such as ancient woodland sit outside this and carry their own, stricter protections.)
A shortfall confirmed by the metric
This is the definitive one. Once your ecologist completes the statutory biodiversity metric and the post-development figure lands below baseline plus 10%, you have a measured shortfall. That number, not a hunch, decides whether you go off-site and how many units you need.
Where off-site gives a better ecological outcome
Sometimes off-site is simply the better answer for nature. A larger, connected habitat bank can deliver more ecological value than small patches squeezed around a development, and it can line up with local nature recovery priorities. For minor developments from August 2026, off-site delivery is treated on an equal footing with on-site, so this choice becomes more open.
How the main development types tend to fall out in practice:
Urban infill
Reach 10% on-site? Rarely
Off-site units needed? Yes, often most or all
Why? Little space remains after allowing for the building footprint, access and parking
Brownfield redevelopment
Reach 10% on-site? Sometimes, but delivery can be slow
Off-site units needed? Often
Why? High baseline value and sealed ground can complicate on-site delivery
Commercial, industrial and logistics
Reach 10% on-site? Rarely
Off-site units needed? Yes
Why? Floorspace and yard requirements leave little room for habitat that scores well
Residential developments with open space
Reach 10% on-site? Partly
Off-site units needed? Often, for the remaining shortfall
Why? Amenity grassland scores poorly, so genuine habitat is needed to generate on-site units
Rural and edge-of-settlement developments
Reach 10% on-site? More often
Off-site units needed? Sometimes
Why? More land may be available, but the outcome depends on the baseline habitat and proposed design
Sites losing high-distinctiveness habitat
Reach 10% on-site? Rarely at the required quality
Off-site units needed? Likely
Why? Trading rules require like-for-like habitat replacement or something better
Metric pointing to a shortfall?
It helps to know what local units are available before the design is locked in.
See our available habitat banks
What happens after a biodiversity unit shortfall is identified?
Once a shortfall is confirmed, off-site BNG follows a fairly set path from assessment to a discharged planning condition. You don't buy units the moment a gap appears. You confirm the number, find suitable units, secure them, and feed that into your biodiversity gain plan.
The typical sequence looks like this:
Step by step:
1. Baseline and metric. An ecologist surveys the site and runs the statutory biodiversity metric to work out pre- and post-development value.
2. Optimise on-site. The design team pushes on-site habitat as far as it sensibly goes.
3. Confirm the shortfall. Whatever the metric still can't deliver on-site is the number you need to cover off-site.
4. Match the units. You look for units of the right habitat type, in a location that works under the spatial rules (more on that below).
5. Buy and allocate. You're invoiced, you pay, and the units are allocated to your development on the Biodiversity Gain Sites Register. There's no legal agreement for you to negotiate. The 30-year agreement sits between the habitat bank and the local authority or responsible body, and it has to be in place before the site can be registered at all.
6. Gain plan and discharge. The biodiversity gain plan sets out how you'll reach 10%, and the local planning authority approves it before the condition is discharged.
Two things worth knowing. A habitat bank doesn't run your survey or write your gain plan; that sits with your ecologist. What it provides is the registered off-site units and the support to match them to your scheme. And the earlier you start step four, the fewer surprises you'll hit on availability and price later.
How to choose an off-site BNG solution
Consider off-site units on four things: if the habitat type matches what you're losing, if the location works under the spatial rules, whether the site is properly registered and legally secured, and if the units are actually available when you need them.
Habitat suitability
The metric's trading rules mean you can't offset the loss of one habitat with just any replacement. Higher-distinctiveness losses need higher-distinctiveness gains, of the same broad type or better. A good habitat bank will tell you which of its habitats can offset your specific losses.
Location and the spatial rules
Where units come from affects how many you need. Under the statutory metric's spatial risk multiplier, units created in the same local planning authority or National Character Area as your development count at full value. Units from further away are discounted, so you need more of them to deliver the same gain. Buying locally usually means buying fewer units. (These boundaries are being reformed towards Local Nature Recovery Strategy areas during 2026, which should widen the local pool, but proximity still counts.)
Registration and legal security
Units only count once the gain site is on the Biodiversity Gain Sites Register and that one fact does most of the checking for you. A site can't be registered until the habitat is legally secured for at least 30 years, through a Section 106 agreement or a conservation covenant with the local authority or a responsible body, and until a habitat management and monitoring plan is in place. So if the units are on the register, that work is already done, and three decades of management sit with the provider rather than with you.
Timing and availability
The right habitat type, in the right place, in the right quantity, isn't guaranteed to be sitting there when you need it. Availability tightens as demand grows, and NSIP schemes entering the market from November 2026 are expected to absorb a large share of units. Early conversations protect your programme.
This is where a regional specialist earns its place. Habitat Banks West Midlands creates and manages registered habitat banks across Staffordshire, Birmingham and the Black Country, Warwickshire and the wider region, with woodland, heathland and grassland sites, and connects developers with local units suited to their scheme. Because the sites sit in the region, they tend to hold full value under the spatial rules for developments nearby.
Working out whether local units suit your scheme?
Send us your metric summary and site location, and we'll tell you whether suitable units are available.
Talk to us about off-site units
Frequently asked questions
Can I combine on-site and off-site BNG?
Yes, and most schemes do. You deliver what you sensibly can on-site and buy the rest off-site. For minor developments, from 6 August 2026 you can weigh on-site and off-site options together rather than having to maximise on-site first.
When should I secure biodiversity units, before or after planning?
You can start looking well before planning is decided, and it's usually wise to. Units are formally allocated as part of discharging the pre-commencement biodiversity gain condition, but checking availability and rough cost early stops off-site delivery becoming a bottleneck later. You don't want to find the units you assumed would be there have already gone.
Can off-site BNG be outside my local planning authority?
Yes. Off-site units can come from outside your LPA. The catch is the spatial risk multiplier: units from outside your LPA or National Character Area are discounted, so you need more of them to deliver the same gain. Sourcing locally generally means buying fewer units.
What's the difference between off-site units and statutory biodiversity credits?
Off-site units are bought from a habitat bank or landowner on the open market. Statutory biodiversity credits are bought from the government and priced deliberately high as a last resort, for when no suitable units can be found. The hierarchy expects you to exhaust off-site options first. One exception: if you need less than 0.25 units, you can buy credits without having to prove off-site options were unavailable - it’s just likely to be a more expensive option.
How is my shortfall calculated?
Your ecologist runs the statutory biodiversity metric, which scores habitats on type, size, condition and location, both before and after development. If the post-development score is below your baseline plus 10%, the gap is your shortfall, and that's what off-site units cover.
Who manages the off-site habitat, and for how long?
The habitat bank or landowner manages it, for a minimum of 30 years, secured through a Section 106 agreement or a conservation covenant. As the developer, you're buying units backed by that long-term commitment, not taking on the management yourself.
What if there aren't suitable units available?
It happens, especially for particular habitat types or in high-demand areas. Options include widening your search (accepting the spatial discount), adjusting the on-site design to shrink the shortfall, or, as a genuine last resort, buying statutory credits. This is exactly why starting the search early matters.
Does every development need off-site BNG?
No. Plenty of schemes deliver their full 10% on-site, and some are exempt altogether, including, from August 2026, many sites of 0.2 hectares or less. Off-site BNG is for developments that can't close the gap within their own boundary.
Find the Right Off-Site BNG Solution for Your Scheme
Off-site BNG isn't a sign something's gone wrong. It's a planned, regulated route for the many sites that can't fit a full 10% gain around the homes, roads and buildings they exist to deliver. The developments that handle it smoothly are the ones that read the metric early, work out the shortfall, and line up suitable units before the design is fixed and before availability tightens.
If your ecological assessment points to a shortfall, the next step is to find out what off-site units are available in your area and whether they suit the habitats you're losing. Habitat Banks West Midlands works with developers across the region to match schemes with local, registered biodiversity units, and to support the allocation process once you've found the right fit.
Send your metric summary and site location, and we'll come back with the units that suit your scheme and when they can be allocated.
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