Biodiversity net gain plan in London

Who is exempt, and who is not

Householder applications are exempt. That means extensions, conservatories and loft conversions to an existing home do not need a plan. Permissions granted by a development order, including permitted development, are exempt too.

A further group of small impacts is excluded by the de minimis rule: where the development affects less than 25 square metres of on-site habitat, and less than 5 metres of linear habitat such as a hedgerow.

Two changes took effect this summer. Sites of 0.2 hectares or below are now exempt unless priority habitat is affected, and the self-build and custom-build exemption has gone for new applications. So a single new house on a small plot can now fall outside the rules, provided no priority habitat is touched.

When the rules reach a London householder

Schemes that are not householder applications need a closer look: a new dwelling in a rear garden, a flat conversion with a landscaping change, or a garage that becomes a separate home. For each one we test the site area, the habitat affected and any priority habitat before saying whether a plan is needed.

Even where the exemption applies, the application form must still say whether the biodiversity gain condition applies and why not. We complete that statement on every submission so the application is not made invalid by an empty box.

If a site is on or near a protected area, a mature tree group or an overgrown plot, we flag it in the free check. Do not clear the plot before you speak to us, and keep dated photographs of how it looks today.

What a BNG plan contains

The core is the completed metric calculation of the site's value before development, followed by the value after, using the habitat types, area, condition and strategic significance of each parcel. Alongside it sit a baseline survey, a map of habitat parcels and a short statement of the gain proposed.

For smaller sites there is an optional small sites metric. It is open to residential schemes of one to nine dwellings on a site of up to one hectare, but not where priority habitat, protected sites or protected species are present.

The plan then fixes how the gain is delivered and maintained. We draw the proposed planting, green roofs, hedgerows and ponds on the landscape layout so officers can match each unit in the calculation to a feature on the sheet. Our new build drawings include that layout.

On site, off site or credits

The gain can be achieved in three ways: on the development site, through registered off-site gains on the national Biodiversity Gain Site register, or, as a last resort, by buying statutory biodiversity credits.

Since this summer, for non-major development, on-site enhancement, on-site creation and registered off-site gains sit at the same level of preference. That gives a small plot more freedom to choose the route that suits the site.

We explain the options and the likely cost in plain terms before you commit, and we do not recommend off-site units where an on-site design would work as well.

How councils treat it and what it means for timing

National policy says plans should set local BNG standards above the statutory requirement only for specific site allocations, so for most London homes the figure is the national one.

Because the condition bites before work begins, the plan needs to be ready once permission arrives. We prepare it in step with the planning drawings so there is no gap between permission and starting on site. If that timing matters, speak to us about our planning consultant service, which sequences the application and its conditions.

Our independent check applies here as well: a second chartered technologist, never the person who prepared the metric, checks the calculation and the landscape sheet before they are submitted.

Price and next step

A BNG plan has no list price. The work depends on the number of habitat parcels and whether off-site units are needed, so you receive a fixed quote after a free constraints check.

Send us the address and what you want to build. We will say whether the condition applies, what the plan needs, and what it is likely to involve. For the rest of the application, see our planning drawings service.