Make on-site biodiversity gains as a developer

Why developers need to make on-site gains 

Under mandatory biodiversity net gain (BNG) legislation, developers must deliver 10% BNG, as measured by the statutory biodiversity metric. 

The guidance on this page assumes a development is subject to BNG. 

There are 3 ways a developer can achieve 10% BNG. 

1. Enhance and restore biodiversity on-site (within the red line boundary of a development site). 

2. If developers cannot achieve all of their BNG on-site, they can deliver through a mixture of on-site and off-site. Developers can either make off-site biodiversity gains on their own land outside the development site, or buy off-site biodiversity units on the market.  

3. If developers cannot achieve on-site or off-site BNG, they must buy statutory biodiversity credits from the government. This should be a last resort. The government will use the revenue to invest in habitat creation in England.  

You can combine all 3 steps, but must follow the steps in order. This order of steps is called the biodiversity gain hierarchy. 

This guidance is about step 1 – how to enhance and restore biodiversity on-site.  

Other work you can count as part of your on-site BNG  

If you’re already creating or enhancing habitat as part of your development, you may be able to count this towards your BNG, as part of your biodiversity metric calculation. The same rules on what you can count apply across both on-site and off-site BNG.  

Depending on the scheme, it may only count in part towards your BNG or it may count in full. There is more information available on what you can count towards a development’s BNG. 

The rules that apply to on-site BNG 

In general, the same requirements apply whether you are doing on-site or off-site BNG.  

On-site and off-site requirements that are the same  

Whether you are relying on on-site or off-site habitat enhancements, you must:

• achieve 10% BNG
• do a survey of habitat before development and use the statutory biodiversity metric to prove the accurate calculation of the biodiversity value of habitats before and after development, and if you have met your 10% BNG 
• complete and submit a biodiversity gain plan after being granted planning permission 

Differences between on-site and off-site rules: legal agreements and 30 years of maintenance 

There may be differences to developers’ obligations when delivering on-site as opposed to off-site BNG, in relation to: 

• management and monitoring – this may be in the form of a habitat management and monitoring plan (HMMP)  
• a legal agreement with a local planning authority (a section 106 agreement) or responsible body (a conservation covenant) 
• a commitment to maintain the BNG for at least 30 years 

These obligations are mandatory for off-site BNG but only mandatory on-site for ‘significant’ on-site habitat enhancements. 

Significant on-site enhancements 

Significant enhancements are areas of habitat enhancement which contribute significantly to the proposed development’s BNG, relative to the biodiversity value before development.

Retention of existing habitat does not count as an on-site enhancement.

What counts as a significant enhancement will vary depending on the scale of development and existing habitat, but these would normally be: 

• habitats of medium or higher distinctiveness in the biodiversity metric 
• habitats of low distinctiveness which create a large number of biodiversity units relative to the biodiversity value of the site before development
• habitat creation or enhancement where distinctiveness is increased relative to the distinctiveness of the habitat before development  
• areas of habitat creation or enhancement which are significant in area relative to the size of the development  
• enhancements to habitat condition, for example from poor or moderate to good  

Examples of significant enhancements include creating a wildflower meadow or a nature park. 

The maintenance of these significant enhancements must be secured with a legal agreement (planning obligation or conservation covenant) or planning condition for 30 years in the same way as off-site gains. LPAs will consider the most appropriate mechanism and this will need to be agreed at the planning permission stage.

LPAs may also require legal agreements for wider planning policy reasons for other on-site enhancements or retained habitats which do not fall into the ‘significant enhancements’ category. For example, where these are expected to contribute to locally important species or ecological networks. Examples include amenity planting areas or individual street trees which may be significant depending on circumstances. Check with your LPA for more guidance or a local plan which explains any local requirements. 

Non-significant enhancements 

Non-significant enhancements are habitat enhancements whose loss will not significantly decrease the development’s biodiversity value. They should still be included in your metric calculations.

Examples could include private gardens which have a low distinctiveness value, or container planting. These enhancements do not normally require maintenance provisions, so for non-significant enhancements, you do not need to have an HMMP, legal agreement or commitment to maintain them for 30 years.  

Selling excess on-site gains 

If you make on-site gains in excess of the mandatory 10% BNG, you can count these towards another development’s BNG. This could be another of your own developments, or any other development.     

Example: a developer achieves 20% on-site BNG. This is in excess of the required 10% BNG. 

Where there are local policies requiring more than 10% BNG, you may need to follow these, for example if an LPA requires 20% BNG, a developer can only sell the excess above 20%.  

If you intend to use excess on-site enhancements from a development for another development, they should be treated as off-site gains for the development that they are counted towards. All the other development’s requirements for making off-site gains must be met, including: 

• securing with a legal agreement 
• registration in the biodiversity gain sites register 
• allocation to the other development   

Significant on-site gains must be subject to a planning condition, planning obligation or conservation covenant. When selling excess on-site gains, one planning obligation or conservation covenant may fulfil the need to secure significant on-site gains and the other development’s need for off-site gains to be legally secured. 

How to plan for BNG on-site 

1. Project design for BNG  

When designing on-site habitat creation and enhancement, you’ll need to consider whether it will be possible to maintain and monitor the habitat over 30 years. You may need to consult a competent person with appropriate training and experience in habitat identification, creation and management, who can advise on what BNG creation or enhancements will be feasible on your site. This could be an ecologist or landscaping professional, for example.  

Examples of questions to consider include: 

• will soil conditions be suitable for your plans? 
• will there be an access point for equipment needed to maintain the habitat, such as a mower? 
• how might pets living on the development affect your plans? 
• is this plant species suitable for the local area? 

It is important that the plants and trees used to deliver your BNG are free from pests and diseases. Source plants and trees from reputable nurseries or suppliers with plant health management standards in place, for example, nurseries with Plant Healthy certification or similar.   

You should take into account the following conditions which could impact on your BNG plans:  

• climate  
• geology and topography  
• agricultural land status  
• soils and substrates  
• contaminated land  
• hydrology and drainage  
• flood risk zones  
• landscape character and designations  
• biosecurity 
• invasive plant species 

If you plan tree planting, you may consider:  

• the urban tree manual published by Forest Research on GOV.UK 
• the National Model Design Code on GOV.UK 

2. Use the metric and submit a biodiversity gain plan metric

Follow the guidance for: 

• applying for planning permission and creating a biodiversity gain plan 
• securing your gains with a legal agreement

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• include all planned on-site gains as part of your calculation. calculation 

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5. Get planning permission 

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6. Submit a biodiversity gain plan   

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Include all your planned enhancements in the biodiversity gain plan.  Your site designs and HMMP should show the LPA how you will fund, maintain and monitor enhancements for 30 years. years.  

YouThe canLPA findhas 8 weeks to approve or refuse your LPA. biodiversity gain plan.

7. Manage on-site BNG and monitor the habitat 

Once the LPA has approved your gain plan and you have any legal agreements and planning permissions in place, you as the landowner are responsible for doing the habitat creation, enhancement and management work to deliver BNG on-site as set out in your plans. This work should start as soon as possible or at least within 12 months of the development commencing.  

You are also responsible for monitoring and reporting on this to the LPA.  .

Best practice guidelines for on-site BNG 

British Standards 8683 - Process for designing and implementing BNG, from the British Standards Institution (BSI). There is a cost to buy this for non-BSI members. 

Guidance for local planning authorities (LPAs) 

There is more information for LPAs.

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