Hard landscape elements
Some of the functional elements that are used in green roofs include:
- non-vegetated zones
- retaining edges
- drains and gutters
- planting containers
- topographical construction
- a range of other elements, not discussed in detail here, such as:
– harness attachment points
– controller boxes/solenoid boxes (to house irrigation components)
– decorative and functional landscape elements such as decking, paving, seating, shade protection, ponds and lighting.
The colour of materials should be considered as this will affect their heat gain. Consider location of shade structures as additional elements.
Non-vegetated zones are used to group roof penetrations, vent pipes and other upstands and assist in lateral drainage. They are generally constructed with large diameter aggregate rock or ballast (16-32 mm size), rather than the growing substrate, and provide additional lateral drainage into the roof drains. They are usually between 300-500 mm wide and are separated from the roof perimeter ballast by metal edging installed around the planting area. Similar vegetation-free zones may be created through use of paving slabs or ballast to provide access pathways across the green roof, or as firebreaks on very large roofs.
Edging can be used to define and the planting substrate from non-vegetated zones across a green roof. It can include concrete, stainless steel, recycled plastic or aluminium products; L-shaped edges are installed above the filter sheet and often have perforations to allow drainage through the profile.
Roofs with a parapet that extends above the roof deck require installation of a cover (flashing) to protect the building fabric. This should be included in the waterproofing installation to ensure that membrane terminations, and any areas of membrane extending over the vertical and horizontal surfaces of the parapet, are not exposed.
Drains and gutters
All drains must be accessible for maintenance, protected from blockage by leaf litter and substrate wash, and housed with inspection chambers, drain covers, filters or strainers. Inspections after construction, following storms and every three months are recommended.
Selection of drainage hardware depends on the required function and appearance; examples are provided in the section on drainage here. For drains located flush with the roof surface, a grille should be installed to prevent drain clogging.
Planters must be made from weather resistant materials, and the components must be physically and chemically compatible with each other. Common examples of materials used to build planting containers are powder-coated metal, galvanised steel, ceramic, timber, UV stable plastic and glad reinforced concrete (lightweight concrete).
Blocks of polystyrene foam can be used to build up areas to create mounds or hills without the additional weight of the substrate. Topographical variations on a green roof create different growing conditions and microclimates to increase habitat opportunities for beneficial insects, as well as visual, aesthetic interest.