Flat roofs and balconies

7.1.9Green and proprietary roofs

Green roofs and proprietary roofing systems shall be suitable for their intended use.

Green roofs should:

  • be clearly defined by the supplier as a complete system
  • have supporting data to demonstrate compliance with relevant standards
  • include waterproofing suitable for use in the green roof system.

Rainwater outlets should be accessible and have a visible inspection hatch.

Green roof systems that do not comply with the principles of this chapter should be assessed in accordance with Technical Requirement R3.

The complete green roof should be installed by a contractor trained and approved by the system supplier.

Waterproofing for green roofs should be either:

  • reinforced bitumen membrane
  • mastic asphalt
  • single-ply membrane, or
  • a liquid applied system.

The system should be installed in accordance with the design and the membrane manufacturer’s recommendations. Before covering:

  • the membrane should be visually inspected and electronically tested for waterproofing integrity, faults rectified, and retested before further layers are placed: the results should be made available to NHBC
  • any damage to the vapour control layer should be repaired, using a full width section of membrane.

Other issues that should be taken into account when installing green roofs include the:

  • provision of root barriers
  • height of upstands in relation to soil height and flashings
  • protection, reservoir and filter layers
  • moisture control of the soil.

Table 6: Principles for green roofs