National foreword

This British Standard is the UK implementation of ISO 17620:2025.

The UK participation in its preparation was entrusted to Technical Committee BDY/1, Biodiversity management.

A list of organizations represented on this committee can be obtained on request to its committee manager.

Contractual and legal considerations

This publication has been prepared in good faith, however no representation, warranty, assurance or undertaking (express or implied) is or will be made, and no responsibility or liability is or will be accepted by BSI in relation to the adequacy, accuracy, completeness or reasonableness of this publication. All and any such responsibility and liability is expressly disclaimed to the full extent permitted by the law.

This publication is provided as is, and is to be used at the recipient’s own risk.

The recipient is advised to consider seeking professional guidance with respect to its use of this publication.

This publication is not intended to constitute a contract. Users are responsible for its correct application.

Compliance with a British Standard cannot confer immunity from legal obligations.

This British Standard was published under the authority of the Standards Policy and Strategy Committee on 31 October 2025.

Foreword

ISO (the International Organization for Standardization) is a worldwide federation of national standards bodies (ISO member bodies). The work of preparing International Standards is normally carried out through ISO technical committees. Each member body interested in a subject for which a technical committee has been established has the right to be represented on that committee. International organizations, governmental and non-governmental, in liaison with ISO, also take part in the work. ISO collaborates closely with the International Electrotechnical Commission (IEC) on all matters of electrotechnical standardization.

The procedures used to develop this document and those intended for its further maintenance are described in the ISO/IEC Directives, Part 1. In particular, the different approval criteria needed for the different types of ISO document should be noted. This document was drafted in accordance with the editorial rules of the ISO/IEC Directives, Part 2 (see www.iso.org/directives).

ISO draws attention to the possibility that the implementation of this document may involve the use of (a) patent(s). ISO takes no position concerning the evidence, validity or applicability of any claimed patent rights in respect thereof. As of the date of publication of this document, ISO had not received notice of (a) patent(s) which may be required to implement this document. However, implementers are cautioned that this may not represent the latest information, which may be obtained from the patent database available at www.iso.org/patents. ISO shall not be held responsible for identifying any or all such patent rights.

Any trade name used in this document is information given for the convenience of users and does not constitute an endorsement.

For an explanation of the voluntary nature of standards, the meaning of ISO specific terms and expressions related to conformity assessment, as well as information about ISO's adherence to the World Trade Organization (WTO) principles in the Technical Barriers to Trade (TBT), see www.iso.org/iso/foreword.html.

This document was prepared by Technical Committee ISO/TC 331, Biodiversity.

Any feedback or questions on this document should be directed to the user’s national standards body. A complete listing of these bodies can be found at www.iso.org/members.html.

Introduction

Biodiversity encompasses the diverse spectrum of life found on Earth, spanning genetic, species and ecosystem levels. This includes a wide array of organisms, including plants, animals, fungi and microorganisms, along with the communities they form and habitats they live in. Biodiversity provides essential services for people, including carbon storage, clean water, air and food. It also underpins our wellbeing and is valued for its intrinsic worth.^[1^]

In recent years, recognition of the joint biodiversity and climate crisis has gained pace. Governments, businesses, organizations and the public are not only seeking to protect biodiversity, but also to enhance biodiversity through all sectors of society and the economy, including construction and development.^[23^]

For many years, balancing economic growth with environmental sustainability was seen as a trade-off, either sacrificing the natural environment, or holding back growth in order to protect nature. This is a misunderstanding and several initiatives have emerged wherein development projects play a role in protecting, restoring, and enhancing the environment. One such initiative is Biodiversity Net Gain (BNG).

BNG is a specific, quantifiable outcome from project activities that deliver demonstrable benefits for biodiversity compared to the starting or baseline state of biodiversity.

Between 2015 and 2018, the IUCN published a number of documents on net positive impacts on biodiversity ^[9^]-[13^] including from business^[11^] and conservation perspectives.^[10^] In 2018, the Business and Biodiversity Offsets Programme (BBOP), an international group of 70 companies, government agencies, financial institutions and civil society organizations, published The BBOP Principles on Biodiversity Offsets^[6^] and the Standard on Biodiversity Offsets^[4^] to support developments to achieve BNG in accordance with good practice. These principles aimed to set a benchmark of objectives including adhering to a mitigation hierarchy and avoiding adverse impacts on irreplaceable biodiversity features.

This document provides a conceptual framework for BNG and builds on, and adds to, the foundational work referenced above. It translates the principles and actions to implement them into a process. The aim of this document is to provide a consistent and structured process for designing and implementing BNG that is based on good practice. It is recognized that indicators and metrics for assessing BNG are at various stages of development. This document aims to support their use and development balancing the challenge of measuring the complexity of nature with the need for consistent, transparent and structured processes to halt and reverse loss of biodiversity.

It is intended that this document is of use to actors involved in development including ecologists, planners, biologists, auditors, developers, conservation organizations, land managers, planning authorities and organisations and investors. It can also be used by land managers and organizations aiming to generate BNG through management of their land.

This document is intended for projects of all sizes and for all types of development sectors. It can be applied to any project, including development projects that do not require planning permission or a building permit, as well as land management.

Most development plans and projects involve a logical sequence through the four broad stages of:

preparation;
design;
implementation;
management, monitoring and reporting.

The process of BNG within this document is founded on these stages, with the aim of applying them to small developments with minimal biodiversity impact, as well as large-scale developments involving project option appraisal or strategic planning.

These stages can be put in parallel with those set out in ISO 14001 under the Plan, Do, Check, Act. The steps of the BNG assessment line up with a development project's life cycle and the ongoing delivery of management and monitoring to deliver the gains in biodiversity:

Plan corresponds to the preparation and design stages,
Do corresponds to the implementation and management stages,
Check corresponds to monitoring,
Act corresponds to reporting and adaptive management that follows.

Some activities described in this document and undertaken through a project are refined and updated as the BNG process is implemented. For example, a given project’s biodiversity baseline can be assessed using desk-based studies during the preparation stage, and then updated following site surveys during the design stage. Annex A contains guidance on which activities can be relevant to different stages of the process.

The following projects should be actively avoided:

projects that will negatively impact protected areas or areas under conservation measures, or
projects with relatively high biodiversity for the region, whose destruction of biodiversity cannot achieve BNG.

These projects can follow the process in this document for biodiversity features that are not irreplaceable but cannot claim project-wide achievement of BNG. These projects will transparently and comprehensively refer to the adverse impacts on irreplaceable biodiversity features in communications and reports

The BNG process in this document does not substitute the requirements to assess ecological beneficial and adverse impacts and report them, e.g. as part of an Environmental Impact Assessment (EIA). Rather, this document builds on, and is not intended to repeat, existing good practices for project biodiversity surveys, impact assessments, mitigation and compensation.

NOTE A project can involve requirements to achieve BNG from, for example, a planning requirement or compliance with legislation. This document covers a process to achieve BNG, notwithstanding any such requirements. It does not infer compliance with any planning condition.

1 Scope

This document specifies a process to design, implement, maintain and monitor biodiversity net gain (BNG) outcomes throughout the life cycle of spatially explicit development projects, until the expected outcome on biodiversity has been realized as proportionate to the project.

This document provides a framework to demonstrate that a project:

has followed a process that is based on good practice and indicators of biodiversity change,
is aligned with the vision, goals and targets of the Convention on Biological Diversity and the Global Biodiversity Framework.^[23^]

This document covers terrestrial and freshwater habitats, and intertidal habitats down to the mean low water mark, as the process and methods to deliver net gain for marine habitats are different from the approach set out here. It does not cover the detailed requirements associated with the delivery of biodiversity enhancements or management.

This document is applicable for projects that affect biodiversity and those with limited or no impact on biodiversity, as well as projects aiming to achieve BNG either onsite or offsite, or both.

BNG can be applicable to any sector of industry, including residential, mixed-use, energy, water, extractive industry, transport, communications agriculture, forestry and infrastructure.

2 Normative references

3 Terms and definitions

4 Abbreviated terms

5 Requirements for all stages of the BNG process

5.1 BNG requirements

5.2 Measuring change

6 Preparation

6.1 General

6.2 Recording a commitment to achieving BNG

6.3 Assessing the feasibility of achieving BNG

6.4 Informing decisions on project option appraisal

7 Environmental assessment and design

7.1 General

7.2 Environmental assessment

7.3 Designing BNG

8 Implementation

8.1 General

8.2 Site set up

8.3 Protecting existing biodiversity features

8.4 Importance of time of year

8.5 Recording during implementation works

8.6 BNG agreement

8.7 Handover from implementation to management

9 Management, monitoring and reporting

9.1 Implementation of the MMP

9.2 Monitoring

9.3 Record management

9.4 Reporting

9.5 Handover

10 Auditing

Bibliography

BS ISO 17620:2025

Biodiversity. Process for designing and implementing biodiversity net gain in development projects

Current

Published:

31 Oct 2025