Flat roofs, terraces and balconies

7.1.12Green and biodiverse (brown roofs) – including roof gardens

Green and biodiverse (brown 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 Code of Practice 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 waterproofing layer suitable for use in the green/ biodiverse 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.

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 in installed in accordance with the design and the waterproofing layer manufacturer’s recommendations and integrity tested prior to covering (see integrity testing).

Other issues that should be considered when installing green roofs include the:

  • Provision of a root barrier or use 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.

Intensive green roof on warm roof deck

Extensive green roof on warm roof deck

Intensive green roof on inverted warm roof deck

Extensive green roof on inverted warm roof deck

Table 16: Principles for green roofs

IntensiveExtensive
Features■ Provides a normal garden environment
■ Uses natural topsoil at least 150mm deep and ‘normal’ plants such as grass, bushes, shrubs
and trees
■ Requires regular ‘intensive’ maintenance, i.e. like
a normal garden
■ Requires protection of the waterproofing
membrane from possible damage during maintenance of the garden, e.g. from weeding/ planting
■ Requires minimal maintenance, i.e. annual attention.
■ Types of planting includes sedum in a blanket or modular trays, wildflower blanket, non-blanket solutions using plug plants or hydroseeding.
Structure■ 10° maximum roof pitch unless anti-shear measures are taken, accounting for full weight of wet soil (generally supported by a concrete deck)■ 45° maximum roof pitch deck (profiled metal deck or concrete deck depending on load)
Drainage Falls■ Finished fall of 1:60 at drainage level■ Finished fall of 1:60 at drainage level
Moisture control■ irrigation system may be required.
■ Can be designed to retain some water in order to maintain the vegetation and to reduce run off.
■ irrigation system may be required.
■ Can be designed to retain some water in order to maintain the vegetation and to reduce run off.
Air and vapour control layer■ Fully bonded polyester -reinforced RBM (S2P3), a suitable self-adhesive membrane, or a torch-on
membrane
■ Fully bonded polyester -reinforced RBM (S2P3), a suitable self-adhesive membrane, or a torch-on
membrane
Insulation■ Insulation material should have adequate compressive strength to withstand likely applied loads.■ Insulation material should have adequate compressive strength to withstand likely applied loads.
Roots■ A root resistant element is required above the waterproofing layer. Alternatively, an approved root resistant waterproofing layer can be used. Note: consideration should be given to the potential for large roots to enter and disrupt inverted warm roof insulation, the system provider should be consulted for advice.■ A root resistant element is required above the waterproofing layer. Alternatively, an approved root resistant waterproofing layer can be used. Note: consideration should be given to the potential for large roots to enter and disrupt inverted warm roof insulation, the system provider should be consulted for advice.
Protection and filter layers■ A protection layer (or board) should be placed above the waterproofing layer.
■ A filter layer should be placed above the reservoir layer
■ In accordance with the manufacturer’s recommendations.