Hertfordshire BNG / County planning guidance
Biodiversity net gain in Hertfordshire starts with your site, its habitats and the planning authority. Use this guide to check local policies, understand LNRS scoring and prepare the evidence for your planning application.
ACP helps developers, architects, planners and landowners survey habitats, calculate biodiversity units and plan delivery. We connect the site evidence with chalk-stream constraints, woodland protection and the county’s nature recovery priorities.
Reviewed 7 November 2026 · Hertfordshire LNRS published 24 November 2025
Application date / site area / habitat impacts
Qualifying development in Hertfordshire normally needs to deliver at least 10% Biodiversity Net Gain. The statutory requirement comes from national legislation, not an automatic county-wide policy.
National exemptions changed on 6 August 2026. A planning application submitted from that date may qualify for a small-site exemption when its red-line site is 0.2 hectares or less and no onsite priority habitat is affected.
Certain wholly temporary developments lasting no more than five years may also qualify. The earlier dedicated self-build and custom-build exemption no longer applies to new applications from that date.
The details matter. Some applications have transitional or section 73 provisions. De minimis and householder exemptions have separate conditions. Therefore, never decide exemption based only on the size of a proposed building.
Even if mandatory BNG does not apply, a project may still affect bats, trees, watercourses or protected habitats. These matters can require separate evidence and mitigation.
For the full decision route, see our BNG exemptions guide and the official GOV.UK exemptions guidance.
Ten district and borough councils / county planning role
The ten district and borough councils generally decide ordinary residential and commercial planning applications. Hertfordshire County Council handles minerals, waste and some county development applications. A county address alone does not determine which checklist applies.
| Authority | Adopted plan / operative ecological policy | 2026 update and application note |
|---|---|---|
| Broxbourne Borough Council | Local Plan 2018–2033, adopted June 2020. Biodiversity and natural environment provisions include NEB3 Green Infrastructure. | Work towards a replacement plan is at an early stage. Retain the adopted policy and check current local ecology evidence. |
| Dacorum Borough Council | Core Strategy adopted 2013, including CS26 Green Infrastructure. | The proposed 2041 Local Plan remains in examination, while a separate 2045 scoping consultation closed in October 2026. Both remain emerging. Check Chilterns Beechwoods SAC mitigation where relevant. |
| East Hertfordshire District Council | District Plan adopted October 2018, including NE3 Species and Habitats. | A new plan programme is in preparation. Check the council's current biodiversity questionnaire and validation checklist. |
| Hertsmere Borough Council | Core Strategy adopted 2013 and Site Allocations and Development Management policies adopted 2016. A BNG SPD was adopted January 2024. | The replacement Local Plan's Regulation 19 consultation runs 8 October–19 November 2026. The 2024 SPD predates August 2026 exemptions. |
| North Hertfordshire District Council | Local Plan 2011–2031 adopted November 2022, including NE4 Biodiversity and Geological Sites. | Local chalk streams and wildlife networks may require specific survey evidence. Apply national 2026 rules alongside adopted policy. |
| Authority | Adopted plan / operative ecological policy | 2026 update and application note |
|---|---|---|
| St Albans City and District Council | A new Local Plan was adopted 9 September 2026, replacing the 1994 plan. Biodiversity policy now sits in that current plan. | Use the adopted 2026 plan. Check Chilterns Beechwoods SAC effects and local validation. |
| Stevenage Borough Council | Local Plan adopted 2019; a partial update was adopted July 2026. Environmental policies include SP12 and NH5. | The former 2021 BNG supplementary planning document was revoked. Use the current plan and national guidance. |
| Three Rivers District Council | Adopted 2011 Core Strategy and 2013 Development Management policies, including DM6 Biodiversity, Trees, Woodlands, Watercourses and Landscaping. | New Local Plan Regulation 19 consultation closed 25 September 2026; the draft is not yet adopted. Verify current biodiversity checklist. |
| Watford Borough Council | Local Plan adopted October 2022, including NE3.9, which addresses at least 10% BNG for major applications. | The council's 2026 biodiversity reporting also discusses the county LNRS and completed gain-plan decisions. Check urban habitats and local validation. |
| Welwyn Hatfield Borough Council | Local Plan adopted 12 October 2023, including SADM16 Ecology and Landscape. | A proposed replacement plan to 2043 had Regulation 19 consultation 23 September–5 November 2026. The adopted 2023 plan remains operative. |
| Authority | Adopted plan / operative ecological policy | 2026 update and application note |
|---|---|---|
| Hertfordshire County Council | County planning responsibilities, especially minerals, waste and certain council projects. Also responsible authority for the Hertfordshire LNRS and specialist ecology advice. | A district housing scheme normally goes to its district or borough, not the county planning team. |
Adopted policies / emerging plans / national framework
A local development plan can shape ecological protection, surveys, site design, green infrastructure and habitat enhancement. Its biodiversity policies sit alongside the national 10% statutory objective.
However, the September 2026 National Planning Policy Framework, policies N1(2) and N2(3), restricts additional BNG targets above the statutory requirement. A higher development-plan standard is supported for a specific site allocation, where it is justified and deliverable. Decision-makers are directed not to give weight to other policies seeking a higher gain than the statutory framework.
As a result, do not assume any Hertfordshire authority requires 20% BNG on every eligible site. Check the actual adopted policy, site allocation, national policy and date of the application.
St Albans adopted a replacement Local Plan on 9 September 2026. It wholly replaced the 1994 District Local Plan Review. Use this adopted plan when reviewing biodiversity and ecological networks.
The new plan addresses biodiversity and ecological networks. A scheme near the Chilterns Beechwoods Special Area of Conservation may also need separate Habitats Regulations evidence.
Dacorum's draft plan to 2041 was still in examination in late 2026. Meanwhile, a 2045 scoping consultation ran in September–October 2026. Each process has its own scope and timetable.
For actual applications, start with the adopted Core Strategy, relevant saved policies and current constraints. Then assess any material emerging-plan weight.
Stevenage adopted a partial Local Plan update in July 2026. It also revoked the older Biodiversity Net Gain SPD from 2021. The currently operative plan and national BNG rules therefore take priority.
Hertsmere's Regulation 19 plan remains open for representations until 19 November 2026. Welwyn Hatfield's comparable consultation closed 5 November 2026. Both proposals remain emerging.
Read NPPF policies N1(2) and N2(3) alongside the applicable development plan and site allocation.
Published November 2025 / mapped habitat priorities
The Hertfordshire Local Nature Recovery Strategy (LNRS) was published on 24 November 2025. Hertfordshire County Council is its responsible authority.
The LNRS identifies local nature-recovery priorities and mapped actions. It can guide habitat retention, creation and links between wildlife sites. It also informs the strategic significance part of statutory biodiversity metric calculations.
That does not mean every field within a mapped opportunity automatically receives higher biodiversity units. The habitat intervention must match an eligible mapped action and meet current metric rules.
For practical design work, the council provides an interactive map, written strategy, guidance for developers and ecologists, and GIS data. Its GIS download was updated in September 2026.
Useful next step: View the official Hertfordshire LNRS map and guidance before finalising habitat proposals.
Baseline evidence / mapped actions / proposed habitat
Hertfordshire County Council's published ecology advice makes an important distinction.
For metrics supporting planning applications submitted after 24 November 2025, the council advises setting baseline strategic significance to Low. The post-development score is then assessed against the published LNRS.
| Metric position | What Hertfordshire County Council advises | What the project team should do |
|---|---|---|
| Before development | Baseline Low for applications submitted after 24 November 2025 | Record the application date and use a survey-supported baseline. |
| After development — mapped and matching | High may apply if a proposed habitat action is mapped and the intervention matches that action | Save map evidence, specify the habitat intervention and apply the metric rules. |
| After development — not matching | Low, including useful actions that are not eligible for the mapped-action multiplier | Do not claim an automatic uplift merely because an action helps wildlife. |
| Older application | Existing valid baseline scores may be retained, while post-development strategic significance follows LNRS guidance | Review the earlier submission date and HCC's transitional advice. |
A High strategic significance score can produce a higher metric multiplier where it qualifies. However, neither the LNRS map nor a spreadsheet replaces an ecological survey and habitat condition assessment.
The distinction is especially useful when considering chalk-stream improvements, woodland corridors, species-rich grassland and wetland restoration. Each habitat choice still needs the correct technical evidence.
Read the county’s Ecology Advisory Service guidance alongside the current metric instructions.
Chalk streams / woodland / protected sites / species
Hertfordshire contains chalk-stream catchments and headwaters, including the Mimram, Beane, Lea, Colne, Ivel, Hiz and Oughton systems. Habitat and water quality depend on flows, banks, water chemistry and the wider catchment.
A new pond, watercourse change or wetland habitat is not automatically appropriate. Where a development affects a relevant watercourse, the work may require a river condition assessment and the watercourse metric module.
Hertfordshire has substantial woodland cover, including ancient woodland and connected rural habitats. Protect valuable features first. Trees and hedgerows can have separate planning, survey or biodiversity metric requirements.
The Chilterns Beechwoods SAC includes Ashridge-related protected habitats. Relevant development in areas including parts of Dacorum and St Albans may trigger recreation-related Habitats Regulations Assessment and suitable mitigation, such as SANG or SAMM arrangements.
These are separate from statutory BNG. A 10% biodiversity unit uplift cannot compensate automatically for a protected-site impact. Site-specific location, development type and current council guidance determine the assessment.
Bats, great crested newts, breeding birds, badgers, reptiles and locally important habitats may require specific evidence. An application exempt from mandatory BNG can still need surveys and mitigation.
Seven practical checks / one site brief
Use the worksheet to establish the information worth gathering before commissioning the metric or submitting the application. Record the evidence so the project team can agree a proportionate survey and assessment scope.
| Check | Evidence to record | Next planning decision |
|---|---|---|
| 1. Find the correct authority | Red-line site boundary, district/borough or county development role | Which adopted plan and local list applies? |
| 2. Establish the application date | Submission date, major/non-major status and any section 73 history | Which BNG rule and transition applies? |
| 3. Test the exemption conditions | Total red-line area, priority habitat, development type | Is a specific national exemption relevant? |
| 4. Survey and map existing habitat | UKHab parcels, condition sheets, trees, hedges, watercourses and photos | What is the defensible metric baseline? |
| 5. Check protected sites and species | SAC/SSSI/LWS context, survey needs and ecological records | Are separate assessments or mitigation needed? |
| 6. Match the LNRS | Proposed habitat, official mapped action and supporting evidence | Can post-development High strategic significance be justified? |
| 7. Plan delivery | Onsite space, off-site options, 30-year security where required and timetable | What gain-plan and habitat management evidence is needed? |
Use the completed worksheet to agree the survey scope, habitat design and planning timetable with your ecologist.
UKHab / condition evidence / original metric workbook
Hertfordshire County Council's Ecology Advisory Service publishes unusually practical expectations for survey evidence.
For a development subject to BNG, a proportionate evidence package may include:
HCC notes that a summary sheet or PDF alone does not replace the original metric workbook. Therefore, provide the calculation and its underlying ecological evidence together.
Grassland surveys can be season-sensitive. HCC's advice identifies mid-May to mid-August as an important grassland assessment period. If timing limits the evidence, document those limitations and determine the appropriate next step.
Our BNG survey service and BNG assessment service explain how the baseline supports planning.
Application evidence / local validation / gain-plan approval
When statutory BNG applies, national application-stage requirements ordinarily include:
A planning authority can also request necessary and proportionate additional information under its current published local list. The applicant must use the correct district or borough list and application type. Read the local requirements alongside the national rules applying on the submission date.
Once permission has been granted for an in-scope development, the final Biodiversity Gain Plan must normally be approved before work begins. That is a later statutory stage, not a universal national requirement to submit a complete final gain plan with the original application.
See ACP's Biodiversity Gain Plan guidance and current GOV.UK planning guidance.
Current metric / onsite and off-site / long-term management
The metric measures the value of existing habitats and proposed changes. Inputs include habitat type, area or length, condition, strategic significance and delivery risk.
As at 7 November 2026, the current government statutory biodiversity metric version is 1.1.0, published 3 November 2026. Some smaller schemes qualify for the separate Small Sites Metric. Eligibility must be checked, not assumed.
For major development, the gain hierarchy continues to favour suitable onsite improvements before registered off-site units. For eligible non-major applications made from 6 August 2026, onsite and registered off-site gains may be treated at an equivalent level. Statutory biodiversity credits remain last.
Where significant onsite gains or registered off-site gains are used, a legal arrangement and long-term management are generally needed for at least 30 years.
Hertfordshire County Council operates a BNG site matching service that connects interested developers with landowners. Before selecting units, check registration, habitat type, legal security and allocation against the project’s requirements.
Read more about statutory biodiversity metric calculations, off-site biodiversity units and the Habitat Management and Monitoring Plan.
Council planning records / evidence and approval stages
These council records illustrate how planning evidence moves from application to gain-plan approval.
Application 6/2026/1453/COND addresses the Biodiversity Gain Plan, Habitat Management and Monitoring Plan and construction management conditions attached to permission 6/2026/0205/MAJ.
The record shows why a project team should coordinate ecological submissions and management responsibilities before starting work.
Watford’s 2026 Biodiversity Duty Report records three approved Biodiversity Gain Plans during its reporting period. It also explains the council’s approach to the Hertfordshire LNRS and Local Plan policy NE3.9.
For a new proposal, align the baseline evidence, gain-plan approval and subsequent monitoring arrangements.
Scope / survey / practical delivery
Step 1 — Identify what applies. Send us the site location, red-line plan, intended works and likely application date. We establish the relevant council route and initial ecological questions.
Step 2 — Gather usable evidence. The scope may include UKHab mapping, condition assessments, a current biodiversity metric and targeted ecological survey work. We also consider LNRS alignment and protected-site constraints.
Step 3 — Design a deliverable approach. We examine suitable habitat retention and enhancement, potential off-site shortfalls and realistic long-term management. This provides the project team with clear planning-stage next steps.
Early advice may reduce unnecessary redesign and poorly timed survey work. It also helps align habitat design, the metric and the application timetable.
For the regional context, explore biodiversity net gain in the East of England.
Practical answers / planning evidence
No. Statutory 10% BNG normally applies to qualifying development, but exemptions and transition rules exist. Each application's type, date, red-line boundary and priority habitat impacts matter. Other ecological duties can still apply to exempt work.
From 6 August 2026, a qualifying application on a site of 0.2 hectares or less may be exempt if it does not affect onsite priority habitat. The exemption is conditional, and older or section 73 applications may need a separate review.
There is no automatic county-wide 20% statutory requirement. National BNG is normally 10%. Local ecological policies still apply, while September 2026 NPPF limits additional mandatory percentages above the statutory objective.
Hertfordshire County Council published the Local Nature Recovery Strategy on 24 November 2025. It identifies local priorities and mapped actions. Its maps are an important design reference but do not replace a habitat survey.
For metrics supporting applications submitted after 24 November 2025, the county's published ecology advice says baseline strategic significance should be Low. Higher post-development scoring depends on matching an appropriate mapped LNRS action.
No. A higher metric multiplier can only apply where the relevant strategic significance rules are met. HCC requires evidence that the proposed intervention matches the mapped action. Unmapped nature-recovery work may still be valuable without that uplift.
The district or borough council usually determines ordinary housing and commercial applications. Hertfordshire County Council handles minerals, waste and some county development. Confirm the actual site boundary and local validation list before submitting.
Possibly. Some schemes may affect the Chilterns Beechwoods SAC and need Habitats Regulations Assessment or relevant recreation mitigation. BNG cannot replace those separate duties. Site location and development type determine the route.
National application-stage BNG information is normally required where the scheme is in scope. The final Biodiversity Gain Plan is generally approved after permission and before development starts. A council may seek justified further evidence under its local list.
Potentially, provided a suitable gain site is legally secured, registered and its units are allocated correctly. HCC’s matching service connects developers and landowners. Check the habitat type, registration and allocation before choosing units.
The current published statutory biodiversity metric on 7 November 2026 was version 1.1.0, updated 3 November. Always verify the government tool version at the assessment date and use the Small Sites Metric only if eligible.
Share the site postcode and red-line plan, project description, current drawings, existing ecology reports and planned application date. If known, include the council and proposed habitat changes. We can then advise on a proportionate scope.
Talk to ACP / Site enquiries
Tell us where the site is, what you plan to build and how far the application has progressed. We’ll use that context to discuss the surveys, calculations or plans your project needs.
What to have to handA red-line plan, an existing ecology report or a request from the council can help us scope the work. Start with whatever you already have.
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Hertfordshire BNG
Reviewed 7 November 2026.
