Building Back Biodiversity: What the 10% Net Gain Planning Rule Means for You

In every architectural project, we ask: can we leave a place better than we found it?

From February 2024, this principle is no longer a choice - it’s the law. All new developments in England, from a ten-home site to a suburban infill, must deliver at least a 10% improvement in biodiversity. This requirement - part of the 2021 Environment Act - reshapes the role of architecture and planning in environmental repair.

A courtyard designed by RISE Design Studio where architecture and ecology meet — native planting, filtered light, and layered habitats create a living space that gives more than it takes.

But at RISE, we don’t see it as a burden. We see it as an opportunity to design with nature, not just around it.

From Loss to Regeneration: A New Chapter for Development

Biodiversity Net Gain (BNG) is a planning condition with soul. It requires us to measure what exists in the natural environment before we build - and ensure we leave behind more than we took. It asks for more trees, more habitat, more life.

And it lasts. At least 30 years of legally secured ecological enhancement - a quiet contract between your project and future generations.

Yet this isn’t simply box-ticking. Biodiversity isn’t numbers on a spreadsheet. It’s the sparrows in your hedgerow. The wildflowers in the verge. The oak that stood before us and will outlive us.

The law now says: value that. Multiply it.

Who It Affects — And Who It Doesn’t

BNG is required for most developments in England. But there are exceptions — and you might fall into one.

You're exempt if:

• You’re extending your own home (householder applications).

• Your development is small and avoids sensitive habitats (under 25sqm of habitat impact).

• Your proposal was submitted before February or April 2024, depending on its size.

• You’re building your own home on a small site (up to 9 homes on ≤0.5 hectares).

• Your project is restoring nature for someone else’s BNG plan.

But even if exempt, we’d argue: build biodiversity in anyway. Not because you have to, but because you can.

On-Site, Off-Site, or On-Paper?

There are three routes to delivering your biodiversity uplift:

1. On-site – the ideal. Enhance what's already there. Plant trees. Sow wildflower meadows. Reintroduce ponds. Create habitats with depth and character.

2. Off-site – if you can’t fit all 10% into your site, you can deliver some on land you own elsewhere, or purchase biodiversity units from approved sites.

3. Credits – the last resort. Buy government-issued biodiversity credits to offset your shortfall.

The hierarchy is clear: first try to restore where you build. The further you stray, the less meaningful the gain — and the more expensive it gets. At over £80,000 per biodiversity unit, this is not the cheap way out. Nor should it be.

How It’s Measured — and Why You’ll Need a Specialist

There’s no guesswork here. DEFRA’s Biodiversity Metric — a weighted system of “biodiversity units” — assigns value to habitats based on distinctiveness, condition, and strategic significance.

But understanding it requires expertise. Habitat distinctiveness, nesting seasons, soil types — all factor in. That’s why we recommend bringing in an ecologist at the early design stage. This isn’t window dressing. It’s integral to your site strategy, your planning success, and the long-term impact of your project.

Nature, Designed In

We’ve always seen architecture as more than buildings. It’s about relationships — between space and sunlight, materials and meaning, people and place. Biodiversity is part of that web.

Think bat boxes concealed in timber cladding. Bird habitats embedded in brick walls. Gardens designed to feed pollinators. Roofs that harvest rain and grow sedum.

Every detail is a chance to stitch the built and the living world closer together.

A Question of Justice

This isn’t just about hedgerows and hedgehogs. Biodiversity is tied to clean air, mental health, and social equity.

When Ella Adoo-Kissi-Debrah died in 2020 — the first person in the UK whose death certificate cited air pollution as a cause — it shone a light on environmental inequality. Greener neighbourhoods are healthier neighbourhoods. And too often, they’re the preserve of the wealthy.

BNG pushes back. It brings green infrastructure to the fore of all developments, not just the flagship ones.

How to Make It Work for You

Done well, a robust BNG strategy reduces planning risk, improves saleability, and connects your development with a deeper purpose. Done badly — or late — it can delay your project or saddle you with costlier offsets.

Here’s what we recommend:

• Appoint an ecologist early (Stage 2–3).

• Incorporate natural systems into the architecture, not as afterthoughts but as design drivers.

• Design with place in mind — native species, local habitats, contextual planting.

• Let some of the site go wild — it’s good for biodiversity, and for us too.

Looking Ahead

There’s a risk that this policy becomes another version of carbon offsetting — biodiversity tokenised and exported elsewhere. But it doesn’t have to be.

If we, as architects, developers, and homeowners, take responsibility for our plot — however modest — we can seed real change.

At RISE, we believe that architecture can, and must, be regenerative. BNG is not a limit. It’s an invitation.

To repair what’s been lost.

To design a future that thrives.

To build not just for today — but for life.

Need help navigating BNG?
We work hand-in-hand with ecologists and planners to embed biodiversity at the core of every project. If you're starting a development and want to make sure you meet - or exceed - your obligations, get in touch. We'll help you design something that lasts, for both people and planet.

If you would like to talk through your project with the team, please do get in touch at architects@risedesignstudio.co.uk or give us a call on 020 3947 5886

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