This article features additional guidance for specific habitats or design cases.
Overlapping habitats
When measuring habitat parcels, the site should be viewed from above and measured as a 2-dimensional area. For some habitats, overlapping is possible.
Individual trees
For individual trees, the table below can be used to calculate an approximate area. This is based on the root protection area of trees based on their diameter at breast height, derived from BS 5837:2012.
Tree size class | Diameter at breast height (cm) | Area equivalent (ha) |
Small | 7.5 - 30cm | 0.0041 |
Medium | 30 - 60cm | 0.0163 |
Large | 60 - 90cm | 0.0366 |
Very large | Above 90cm | 0.0765 |
When recording individual trees in the tool, the area beneath the canopy should be measured and classified separately. The area of individual trees is not included within the total area, but their biodiversity units are included. If your development includes the planting of new trees, you do not need to include their area when balancing between baseline and created.
Green roofs and green walls
When recording green roof habitats in the tool, the area should be subtracted from the building area to prevent double counting.
Like individual trees, the area of green wall habitats is not included within the total area as they are calculated based on their vertical area, but their biodiversity units are included. If your development includes green wall habitats, you do not need to include their area when balancing between baseline and created.