7.1.12 Green and biodiverse roofs – including roof gardens
Green and biodiverse roofs shall be suitable for their intended use.
Green and biodiverse roofs should:
- be designed with a finished fall at the waterproofing layer of 1:60 (1°) minimum
- be designed in accordance with the GRO Green Roof Code of Best Practice 2021 and CIRIA C753 SuDS Manual 2015
- have a certified waterproofing system that is endorsed by the manufacturer as fully suitable to be specified for a green sustainable roof design
- be designed to take account of wind uplift and flotation
- have supporting data to demonstrate compliance with relevant material standards and codes of practice
- include a waterproofing layer suitable for use in the specified roof system
- have rainwater outlets that are accessible and have a visible inspection hatch.
Green and biodiverse roof systems that do not comply with the principles of this chapter should be assessed in accordance with Technical Requirement R3.
Both the green/biodiverse roof system and the waterproofing layer should be installed by a contractor trained and approved by the system supplier.
The waterproofing layer should be either:
- reinforced bitumen membrane
- mastic asphalt
- single-ply membrane, or
- a liquid applied system (cold or hot melt).
The system should be installed in accordance with the design and the waterproofing layer manufacturer’s recommendations and integrity tested prior to covering (see Clause 7.1.11, integrity testing of the waterproofing layer).
Other issues that should be considered when installing Green Roofs include the:
- provision of a root barrier or use of a waterproofing layer that is resistant to root penetration in accordance with BS EN 13948
- height of upstands in relation to soil height and flashings
- protection, reservoir and filter layers
- moisture control of the soil.
Table 16: Principles for Green Roofs
Last updated: 2nd January 2025