Green roofs are more than just attractive features, they’re a practical solution to help meet the UK’s new Biodiversity Net Gain (BNG) mandates.
Under legislation introduced in early 2024, most developments must leave nature in a better state than before, requiring at least a 10% net gain in biodiversity.
This article explores how green roofs can deliver that measurable uplift, boosting your BNG score by creating valuable urban habitats.
We also highlight how Gentian’s satellite AI technology provides the data and insights to identify opportunities for retrofitting, implementing, and monitoring green roofs for maximum BNG impact.
Jump to: The BNG Mandate: A New Reality for UK Developers • How Green Roofs Contribute to BNG • Maximise Your BNG Score with Strategic Design • Measuring Biodiversity with Satellite AI (BNG Assessments) • A Partner for a Greener Future
Biodiversity Net Gain (BNG) is now a mandatory planning condition in the UK.
BNG is measured using a standardised biodiversity metric that assigns biodiversity units based on habitat size, type, quality, and location.
In practice, a project’s pre-development habitat value (in units) is calculated, and the post-development value must be at least 10% higher to satisfy the BNG mandate.
Critically, developers are also obligated to manage any new or enhanced habitats for a minimum of 30 years, which means long-term maintenance plans are essential.
To avoid costly planning delays, it’s vital to incorporate BNG early in project design. There are three main routes to delivering BNG: on-site habitat creation or enhancement, off-site habitat gains (on other land or via purchased units), and as a last resort buying statutory biodiversity credits from the government.
On-site measures are typically preferred by planning authorities, with off-site options used if on-site gains fall short.
Learn more about the BNG process on our Biodiversity Net Gain Assessment service page or on our blog with our Guide to Biodiversity Net Gain Assessment (BNG).
Green roofs might be visually striking, but beyond aesthetics they offer tangible biodiversity benefits.
By creating living habitats on otherwise unused roof space, a green roof can compensate for habitat lost to development and support urban wildlife, especially habitat associated with former industrial sites (Open Mosaic Habitat).
In fact, green roofs are recognised as valuable for BNG compliance because they provide new areas for plants and animals to thrive, all while delivering bonus benefits like stormwater management and a positive impact on the Urban Heat Island Effect.
To unlock these BNG gains, a roof must be designed with biodiversity in mind. Here are the key ways extensive green roofs contribute to biodiversity net gain:
A green roof effectively creates a new habitat where none would normally exist.
Rooftop vegetation offers food and shelter for species that would otherwise find only concrete.
Birds and invertebrates, especially pollinators can colonise these oases, directly increasing the amount of habitat available on-site (and thus the biodiversity unit score).
Green roofs help offset habitat loss from construction by replacing green space at height.
In space-limited urban projects, adding habitat on roofs means developers can still achieve net gain even if ground-level opportunities are scarce.
This is why rooftop greening has become a key strategy to counter habitat loss in cities.
Vegetated roofs also function as wildlife corridors in the city.
Birds, bees and butterflies, for example, can hop between green roofs as stepping stones, preventing isolated pockets of nature.
By connecting fragmented urban greenspaces, green roofs enable pollinators and birds to move through the urban landscape safely, enhancing overall ecosystem connectivity.
And where there is a large development with lots of green roofs this can be a significant ‘plateau’ of habitat such as at places like North Greenwich and Barking Riverside in London.
Black redstart's are a key species found on extensive biodiverse green roofs.
A wildflower-rich rooftop habitat can significantly boost a development’s BNG score by providing a high-quality, distinctive ecosystem associated to a certain extent to open-mosaic habitat.
Not all green roofs are created equal when it comes to net gain.
To truly boost your BNG score, a green roof must be designed as a thriving habitat, not just a thin layer of sedum.
Basic sedum mat and wildflower turf roofs score very low under the BNG metric due to their limited ecological value.
To achieve a higher score, opt for a biodiverse extensive roof instead of a monoculture sedum blanket.
Biodiverse roofs mimic natural habitats with a variety of plants, making them far more distinctive and supportive of wildlife.
When selecting vegetation, the use of range of native plant species is imperative
Native wildflowers are adapted to the local environment and provide food and shelter for indigenous wildlife.
A roof planted with natives will attract more local pollinators and birds, enhancing its ecological value.
BNG also factors in habitat distinctiveness (how rare or valuable the habitat is) and condition (its quality).
Biodiverse extensive green roofs are more distinctive than sedum/wildflower mats/turf, but they must also be well-designed to achieve a “Good” condition rating.
Wool carder bee - solitary bees and wasps nest in logs and piles on good biodiverse extensive green roofs.
For example, a biodiverse roof should have varied substrate depths (around 80–150 mm) and include features like log piles or sand mounds to support nesting insects.
Such details ensure the roof qualifies as a high-quality habitat, maximising its unit score.
Finally, consider strategic significance, whether your roof supports broader conservation priorities.
A green roof that aligns with local biodiversity targets (for example, targeting specific species such as the Black redstart (Phoneicurus ochruros) can receive a higher score.
In summary, designing your roof to contribute to specific local species and open-mosaic habitat goals will boost its BNG value.
Whilst good green roofs deliver for Black redstarts the wildflower seeds are an important food source for Linnets in Urban areas.
Accurately measuring biodiversity for BNG compliance has traditionally been time-consuming and costly.
On-the-ground ecology surveys can take weeks (or months) and often must wait for the right season, causing expensive delays. They also require specialist ecologists on site, which can be impractical across multiple or large developments.
Gentian addresses this challenge by using satellite imagery and AI for habitat surveys. Our system analyses high-resolution images to classify habitat types and conditions, then calculates biodiversity units in line with the official metric.
Because this process is automated, it delivers results within days or even minutes rather than months, and it can be 75–90% cheaper per site than traditional surveying methods. Faster data means you can assess sites early and avoid the seasonal bottlenecks that typically slow down projects.
Accuracy remains high. The AI’s habitat mapping achieves more than 97% alignment with expert manual surveys in tests, providing reliable baseline data for your BNG calculations.
And since everything is digital, you can easily repeat assessments over time to monitor habitat progress throughout the 30-year management period.
The result is a transformative, data-driven approach to BNG. Instead of waiting on field surveys, you get near-instant insights to guide design decisions.
For example, one client used our tool to dramatically cut site-scoping time (and cost), giving them a jump on approvals.
By integrating satellite-based BNG assessments, you remove survey bottlenecks and de-risk compliance, making it much easier to plan, implement, and demonstrate a successful Biodiversity Net Gain.
Achieving Biodiversity Net Gain isn’t just a box-ticking exercise, it's a strategic opportunity to create a more resilient and sustainable urban environment.
While the aesthetic appeal of green roofs is clear, their true power lies in their ability to provide measurable biodiversity uplift.
By using innovative, data-driven solutions like Gentian's satellite AI technology, you can move beyond guesswork.
Our precise, scalable, and rapid BNG assessments will empower you to design, implement, and monitor green roofs that don't just look good but also deliver tangible ecological value, ensuring your projects are both compliant and genuinely impactful for a greener future.
The outcome? Projects that meet the 10% net gain mandate and genuinely enhance the local ecosystem. Ready to get started? Enquire about our Biodiversity Net Gain (BNG) assessments today.