BNG Biodiversity Net Gain Monitoring Survey for Homeowners: Do You Need It?
Short answer: probably not. Most homeowners planning an extension, loft conversion, or other householder development do not need a Biodiversity Net Gain (BNG) monitoring survey. BNG requirements apply to larger development projects, not typical residential home improvements.
This guide explains exactly when BNG monitoring does — and does not — apply to homeowners.
When Homeowners Are Exempt from BNG
| Application Type | BNG Required? | | --- | --- | | Householder applications (extensions, conservatories, loft conversions) | ❌ Exempt | | Permitted development (no planning needed) | ❌ Exempt | | New build (1–9 homes on small sites) | ✅ Yes — from 2 April 2024 | | Impacts less than 25 m² of habitat | ✅ De minimis exemption may apply |
The householder exemption is defined in Article 2(1) of the Town and Country Planning Order 2015. It covers the vast majority of residential home improvement projects.
What You Still Need to Do
Even if exempt, you must still complete the mandatory "Biodiversity net gain" question on your planning application form and select the householder exemption.
| Step | Required? | | --- | --- | | Complete BNG question on planning form | ✅ Yes — select householder exemption | | Preliminary Ecological Appraisal | Only if protected species suspected | | Wildlife Assessment Check | Optional — ~£500 for householder via NatureSpace | | BNG metric calculation | Only if development exceeds de minimis threshold |
When BNG Does Apply to Homeowners
Small Sites (1–9 Homes)
If you are building a small housing development (1–9 homes), BNG became mandatory from 2 April 2024. This is a development project, not a householder application.
De Minimis Threshold
Your development may be exempt under the de minimis threshold if:
| Condition | Requirement | | --- | --- | | Area condition | Impact on less than 25 m² of habitat on site | | Linear condition | Impact on less than 5 m of linear habitat (hedgerows) | | Habitat type | No priority habitat affected |
If all three conditions are met, the de minimis exemption applies and no BNG is required.
Future Changes (Expected Before 31 July 2026)
The government has proposed a 0.2 hectare exemption — sites of 0.2 ha or less with no priority habitat affected would be exempt. This is not yet in force. The current BNG framework remains fully applicable until legislation is enacted.
BNG Requirements for Small Housing Developments
If your project is a small housing development rather than a householder application:
| Requirement | Description | | --- | --- | | 10% net gain | Minimum biodiversity net gain using Statutory Biodiversity Metric 4.0 | | Baseline habitat survey | UK Hab classification of existing habitats | | 30-year monitoring | Habitat Management and Monitoring Plan (HMMP) | | Legal securing | Section 106 agreement or conservation covenant |
2025 BNG Costs (If Applicable)
If BNG does apply to your project (e.g., small housing development):
| Item | Cost Range (ex VAT) | | --- | --- | | Preliminary Ecological Appraisal (PEA) | £800–£2,500 | | BNG metric calculation + report | £1,200–£3,500 | | 30-year HMMP | £500–£1,500 | | Off-site units (if needed) | £20,000–£42,000 per unit | | Section 106 / conservation covenant legal costs | £1,500–£4,000 |
For a typical 4-home rural development: £5,000–£15,000 total.
Frequently Asked Questions
Q: Does my rear extension need BNG monitoring?
No — householder applications for extensions, loft conversions, and conservatories are exempt from BNG. You must still complete the biodiversity net gain question on the planning form and select the householder exemption.
Q: My garden extension is 40 m² — do I need BNG?
If it is a householder application, it remains exempt. If it is part of a small housing development (1–9 homes), BNG may apply. The 25 m² de minimis threshold applies to habitat loss on the development site itself.
Q: Can I use my garden for biodiversity net gain?
Gardens and householder extension sites cannot be legally secured for 30-year BNG monitoring. BNG for small housing developments must be delivered on or off the development site with proper legal securing.
Q: Does permitted development need BNG?
No — permitted development (no planning application required) is exempt from BNG. The mandatory biodiversity net gain question applies only to planning applications.
Q: What happens if I don't complete the BNG question on the planning form?
The planning authority will likely reject the application as invalid. Always complete the biodiversity net gain question and select the applicable exemption.
Q: When is a Wildlife Assessment Check useful for homeowners?
A basic Wildlife Assessment Check (~£500 via NatureSpace) is useful if your property has habitats that might support protected species (bats, birds, reptiles). It is not a full BNG survey but helps identify potential planning constraints.