How living walls and roofs will help developers meet Biodiversity Net Gain

So how do living walls, living roofs, podiums and rooftop gardens help developers with BNG?

The CIEEM principles outlines a number of measures to incorporate biodiversity features. These specifically name green roofs, brown roofs and green walls, but we have also included other measures and explained with P&P notes how these relate to living walls, roofs, podiums and rooftop gardens.
1. Green roofs with a diversity of plant species.

• P&P note: More intensive planting with a wider variety of native species (particularly those that are present prior to development), in deeper substrate is more beneficial to local wildlife than an extensive / sedum roof. See living roofs.

2. Brown roofs with a range of substrates.

• P&P note: The concept of the brown roof is to reuse or reproduce the environment of the brown-field site (which are often rich in biodiversity) on the roof of the development, and allow native plants to naturally colonise. See Brown roofs.

3. Green walls created with planting locations built in, or a planting framework added externally.

• P&P note: Similar to roofs, living walls that allow for the planting of a greater variety and size of plants, including native and those known to be beneficial to wildlife are better than walls that designed simply for visual appeal. Some walls host up to 50 plants per square metre – that’s provides a good scope for variety. See Living roof FAQ.

4. Introducing bat and bird boxes, following guidelines.

• P&P note: In the correct circumstances, bird boxes and bat boxes can be introduced to green walls, and should be used by birds and bats. However biodiverse living walls are also a valuable source of food, both in terms of edible plants and the invertebrates that live there. A 2014 study by Caroline Chiquet found that more birds were present in neighbourhoods with green walls than those without. See the Benefits of green walls for more details.

5. Rough or natural stone walls with holes for invertebrates and small birds to use.
6. Habitat creation for locally relevant wildlife habitat types.
7. Provide a range of ‘bug hotels’ with dead wood and stone piles, or purpose-made bug boxes with tubes and drill holes.

• P&P note on 5-7: Green and brown roofs are perfectly good homes for bug hotels, hives, log or stone piles and other habitats, where they can remain undisturbed for years.

8. Native wild flower mixes as an alternative to amenity grassland or verges.
9. Early flowering plants that provide a nectar source for early invertebrates such as bees.
10. Nectar-rich native planting and native species with berries in the autumn within formal landscaping.
11. Species-rich native hedgerows as boundary features.

• P&P notes on 8-11:
• Green roofs make great wildflower meadows, see the Wimbledon Grounds case study, where every one of the roofs has been seeded with a wildlife-friendly flower mix.
• Roofs with a deeper substrate can accommodate bulbs and perennials known to suit pollinators.
• The deeper substrate of landscaped podiums and roof gardens can incorporate native shrubs, even trees. See the Barbican case study.

12. Ponds (not fish stocked) with an irregular and shallow, sloping edges.

• P&P note: Landscape podiums can be designed to encorporate wildlife ponds.

13. Habitat corridors across a site to make a connection with wider habitats.

• P&P note: There have been some studies that have looked at whether living roofs and walls contribute to wildlife corridors, between wild spaces. It seems that living roofs and walls could become wildlife corridors, but there needs to be a higher concentration of living roofs and walls in a given area and these installations need to be larger with more thought given to the planting.