Biodiversity Net Gain Off-Site Units Marketplace Prices August 2026: A Guide for Minor Developments

Last updated: August 12, 2026

Quick Answer: From 6 August 2026, minor developments of 1-9 dwellings in England must comply with mandatory Biodiversity Net Gain requirements. Off-site biodiversity unit purchases now carry equal legal weight to on-site delivery for these sites, and units are available through the DEFRA-registered marketplace at prices broadly ranging from £15,000 to £35,000+ per biodiversity unit depending on habitat type and location. Statutory credits remain available as a last resort but cost significantly more.

Key Takeaways

• The mandatory BNG requirement extended to minor developments (1-9 dwellings) on 6 August 2026, completing the phased rollout under the Environment Act 2021.
• Minor developments must achieve a minimum 10% net gain in biodiversity units compared to the pre-development baseline.
• Off-site biodiversity units purchased through the DEFRA-registered marketplace now have equal legal standing to on-site habitat creation for minor sites.
• Marketplace unit prices in August 2026 vary widely by habitat type, ranging from approximately £15,000 to over £35,000 per biodiversity unit (BU), these are indicative market estimates; always obtain current quotes directly from registered providers.
• Statutory biodiversity credits, sold directly by Natural England, are a valid fallback but are intentionally priced above market rates to encourage private market solutions.
• A Biodiversity Metric calculation (currently DEFRA's Biodiversity Metric 4.0) is required before any planning application submitted on or after 6 August 2026.
• Developers should commission a baseline habitat survey and metric calculation early, ideally at the design stage, not after planning is submitted.
• Failing to meet BNG requirements is a planning condition breach that can block development commencement.

What Is Biodiversity Net Gain and Why Does It Matter for Minor Developments?

Biodiversity Net Gain (BNG) is a legal requirement under the Environment Act 2021 that obliges developers to leave biodiversity in a measurably better state than before development. For minor developments, defined as 1 to 9 dwellings, mandatory BNG took effect on 6 August 2026, the final phase of a staged national rollout.

Before this date, many small developers assumed BNG only applied to larger schemes. That assumption is now incorrect. Any planning application for a qualifying minor residential development submitted on or after 6 August 2026 must demonstrate a minimum 10% biodiversity net gain, calculated using the DEFRA Biodiversity Metric. This applies across England.

For a deeper grounding in the fundamentals, see this plain-language overview of biodiversity net gain and a detailed explanation of what a biodiversity net gain assessment contains.

What Counts as a Minor Development for BNG Requirements?

A minor development, for BNG purposes, is a residential scheme of 1 to 9 dwellings, or a non-residential development with a floor area below 1,000 square metres or a site area under 1 hectare. This article focuses on the residential category.

Important edge cases:

• Permitted development conversions and certain householder applications may be exempt, check with your local planning authority (LPA) before assuming an exemption applies.
• Developments on land that is entirely within an irreplaceable habitat (ancient woodland, for example) follow a separate, more demanding process.
• De minimis exemptions exist for developments with a negligible impact on biodiversity, but these must be formally demonstrated, not assumed.

For a broader look at BNG obligations on smaller projects, the guide on BNG for small development projects covers common scenarios in detail.

What Is the Difference Between On-Site and Off-Site Biodiversity Units?

On-site biodiversity units are created by enhancing or creating habitats within the development boundary, for example, planting native hedgerows, creating a wildflower meadow, or installing green roofs. Off-site units are created on land elsewhere, managed by a registered habitat provider, and purchased by the developer to offset any remaining biodiversity deficit.

Before 6 August 2026, the BNG hierarchy strongly favoured on-site delivery for minor developments. The updated guidance that took effect on that date gives off-site units equal legal weight to on-site provision for minor residential schemes. This is a meaningful shift: a developer of a 4-dwelling infill site with no viable land for habitat creation can now satisfy the full 10% gain requirement entirely through off-site unit purchases, without any planning penalty.

The comparison of off-site versus on-site BNG delivery explains the practical trade-offs between these two routes in detail.

Can Small Developments Use Off-Site BNG Units Instead of On-Site?

Yes. As of 6 August 2026, minor developments can meet their entire BNG obligation through off-site unit purchases if on-site delivery is not feasible or sufficient. The developer's ecologist must still calculate the baseline metric and demonstrate the unit shortfall, but there is no longer a requirement to maximise on-site provision first before accessing the off-site market.

Choose off-site if:

• The site is too small or densely built to accommodate meaningful habitat creation.
• On-site habitat would be of low quality or unlikely to be maintained long-term.
• The cost and complexity of on-site management outweighs the purchase price of off-site units.

Choose on-site (or a hybrid) if:

• The site has genuine green space that can be enhanced.
• The LPA's biodiversity strategy prioritises local habitat connectivity.
• On-site delivery reduces the number of units needed and lowers overall cost.

How Much Do Off-Site BNG Units Cost in August 2026?

Off-site biodiversity unit prices on the DEFRA-registered marketplace in August 2026 vary considerably by habitat type, strategic significance, and geographic location. The figures below are indicative market estimates based on known pricing structures; developers should obtain live quotes from registered providers before budgeting.

A typical minor development of 4-6 dwellings on a previously developed site might require 2-6 biodiversity units to meet the 10% gain threshold, depending on the baseline habitat quality. At mid-range prices, total off-site BNG costs for such a scheme could fall between £40,000 and £120,000, a significant but plannable cost when factored into land appraisals early.

For a detailed breakdown of unit costs and statutory credit pricing, see the guide on the cost of biodiversity units and statutory credits.

Are BNG Unit Prices Going Up or Down in 2026?

Market pricing for off-site BNG units has trended upward through 2025 and into 2026, driven by two factors: growing developer demand as the minor development deadline approached, and a constrained supply of registered habitat providers with sufficient land in the right locations.

The extension of mandatory BNG to minor developments on 6 August 2026 has added a significant new pool of buyers. Early market signals suggest prices for the most in-demand unit types (lowland grassland and new woodland) have risen 10-20% compared to mid-2025 levels. Wetland units, already scarce, command a premium in most regions.

Prices are not fixed. The DEFRA-registered marketplace operates on a negotiated basis between buyers and registered providers, so volume, timing, and habitat type all affect the final price. See below for guidance on negotiation.

Biodiversity Net Gain Marketplace Prices: How to Buy Off-Site BNG Units

Purchasing off-site biodiversity units for minor developments involves several distinct steps. Developers and their ecologists should follow this process for any planning application submitted on or after 6 August 2026.

Step-by-step process:

1. Commission a baseline habitat survey. A qualified ecologist surveys the development site and records all existing habitats using the DEFRA Biodiversity Metric 4.0 methodology.
2. Run the metric calculation. The ecologist calculates pre-development and post-development biodiversity unit values, identifying the shortfall that must be addressed.
3. Determine the off-site unit requirement. After maximising any feasible on-site habitat enhancement, the remaining deficit is the number of off-site units needed.
4. Search the DEFRA-registered marketplace. Access the official habitat trading platform to identify registered providers offering units of the correct habitat type in an appropriate location (ideally within the same local nature recovery network area).
5. Obtain quotes and agree a Habitat Management and Monitoring Plan (HMMP). The provider must commit to managing the off-site habitat for a minimum of 30 years.
6. Register the agreement. The off-site unit allocation must be recorded on the DEFRA biodiversity gain site register before or at the point of planning permission.
7. Submit the planning application. Include the Biodiversity Net Gain Statement, the metric outputs, and evidence of the registered off-site allocation.

For a practical walkthrough of the full report requirements, see what you need in a biodiversity net gain report.

Can I Negotiate BNG Unit Prices, or Are They Fixed?

Prices on the DEFRA-registered marketplace are not fixed. They are set by registered habitat providers and are subject to negotiation, particularly for developers purchasing multiple units or willing to commit early in a provider's habitat creation timeline.

Practical negotiation points:

• Early commitment (before the habitat is fully established) often attracts a lower price.
• Purchasing units from a provider with surplus stock in a given habitat type gives more room to negotiate.
• Bundling hedgerow and area units from the same provider can reduce transaction costs.
• Statutory credits, by contrast, have a fixed government price and cannot be negotiated.

Common mistake: approaching the marketplace after planning has been submitted and under time pressure. This removes all negotiating leverage and often forces acceptance of premium pricing.

When Are Statutory Biodiversity Credits the Right Fallback?

Statutory biodiversity credits, sold by Natural England on behalf of DEFRA, are the correct option when no suitable off-site units are available on the private marketplace. They are intentionally priced above typical market rates to make the private marketplace the preferred route.

Use statutory credits when:

• No registered habitat providers can supply the required habitat type in the relevant geographic area.
• The development timeline is too short to wait for a private marketplace transaction to complete.
• The unit requirement is very small (1-2 units) and transaction costs on the private market outweigh the price premium of statutory credits.

Statutory credits are purchased directly through Natural England's online portal. Payment triggers an obligation on Natural England to fund equivalent habitat creation elsewhere in England. The process is faster than the private market but more expensive, statutory credit prices for some habitat types can be two to three times higher than comparable private market units.

What Are Common Mistakes Developers Make with Off-Site Biodiversity Net Gain?

Starting the process too late is the single most common error. BNG must be addressed before planning submission, not after. Developers who treat it as a post-permission task risk delays, cost overruns, and planning condition breaches.

Other frequent mistakes:

• Assuming an exemption applies without checking with the LPA or a qualified ecologist.
• Underestimating the baseline habitat value of a site. Even a scrubby brownfield site can have measurable biodiversity value that increases the unit shortfall if not properly surveyed.
• Failing to register the off-site allocation on the DEFRA gain site register before submitting the application.
• Choosing the cheapest unit type without checking whether it matches the habitat type lost on-site. The metric requires like-for-like matching in some circumstances.
• Not budgeting for BNG costs in the land appraisal, leading to viability problems later.

The guide on achieving biodiversity net gain without the risk covers risk mitigation strategies in more detail.

Do All Minor Developments Need to Buy BNG Units?

Not all minor developments will need to purchase off-site units. Some sites will have sufficient space and appropriate conditions to meet the 10% gain entirely through on-site habitat creation. Others may qualify for a de minimis exemption if the development has a genuinely negligible impact on biodiversity.

Developments likely to need off-site units:

• Dense infill sites with little or no existing green space.
• Brownfield sites where on-site habitat creation is constrained by ground conditions or layout.
• Sites where the existing habitat baseline is high-quality, making the 10% improvement threshold harder to meet on-site alone.

Developments less likely to need off-site units:

• Rural sites with large gardens or open land that can be managed for biodiversity.
• Sites where the developer is willing to create and manage a meaningful on-site habitat area.

How Long Does It Take to Purchase and Implement Off-Site BNG?

The timeline from initial habitat survey to confirmed off-site unit registration typically runs 6 to 12 weeks for a straightforward minor development, assuming a registered provider is available with suitable units.

Approximate timeline:

• Baseline survey and metric calculation: 2-4 weeks
• Marketplace search and provider negotiation: 2-4 weeks
• Legal agreement and HMMP finalisation: 2-4 weeks
• Registration on DEFRA gain site register: 1-2 weeks

Delays are most common when the required habitat type is in short supply, when the legal agreement requires extensive negotiation, or when the developer has not engaged an ecologist until late in the planning process. Starting at the design stage, rather than after a planning application is drafted, avoids most of these delays.

FAQ

Q: Does BNG apply to a single new dwelling on a garden plot?
A: Yes, if the application is submitted on or after 6 August 2026 and the development does not qualify for a de minimis or other exemption. A single new dwelling is within the 1-9 dwelling threshold for minor developments. Always confirm exemption eligibility with your LPA or a qualified ecologist before assuming the requirement does not apply.

Q: Can a developer use the same off-site unit allocation for multiple planning applications?
A: No. Each biodiversity unit can only be allocated to one development. Once registered on the DEFRA gain site register against a specific planning permission, those units cannot be reused for another site.

Q: What happens if a planning application is submitted without a BNG statement?
A: The LPA can refuse to validate the application or impose a planning condition requiring BNG compliance before development commences. Persistent non-compliance can result in enforcement action.

Q: Are off-site BNG unit prices the same across England?
A: No. Prices vary by region, habitat type, and local supply. Areas with active local nature recovery strategies and higher developer demand tend to have higher unit prices. Always obtain quotes from providers operating in or near the relevant local nature recovery network area.

Q: How long must off-site habitat be maintained?
A: A minimum of 30 years from the date of the habitat management agreement, as required under the Environment Act 2021. This long-term commitment is built into the legal agreement between the developer and the habitat provider.

Q: What is the DEFRA Biodiversity Metric and which version applies in August 2026?
A: The DEFRA Biodiversity Metric is the standardised calculation tool used to measure biodiversity unit values before and after development. Biodiversity Metric 4.0 is the current version applicable to planning applications submitted in August 2026. It assigns unit values based on habitat type, condition, and strategic significance.

Q: Can a developer sell surplus on-site biodiversity units to other projects?
A: Only if the landowner registers the land as a habitat bank through the DEFRA gain site register process. A developer who creates more on-site habitat than required cannot informally sell the surplus, formal registration as a habitat provider is required.

Conclusion

The extension of mandatory BNG to minor developments on 6 August 2026 marks a genuine turning point for small housebuilders across England. Off-site unit purchases are now a fully equal route to compliance, and the DEFRA-registered marketplace provides a structured mechanism to source those units, but prices are not fixed, supply is not unlimited, and the process takes time.

Actionable next steps for developers:

1. Commission a baseline habitat survey and Biodiversity Metric 4.0 calculation at the design stage for any site with a planning application intended for submission on or after 6 August 2026.
2. Budget for off-site BNG costs in the land appraisal, indicative figures of £15,000 to £35,000+ per unit should be modelled against the likely unit requirement.
3. Engage with the DEFRA-registered marketplace early to identify suitable providers and negotiate before time pressure forces a premium purchase.
4. Reserve statutory credits as a genuine last resort, not a first option.
5. Ensure the off-site allocation is registered on the DEFRA gain site register before submitting the planning application.

For developers and ecologists wanting to understand the full scope of their obligations, the guide to biodiversity credits for developers and the eight key BNG planning points are practical starting points. Acting early is the most reliable way to control costs and avoid planning delays on minor development sites in 2026.