Green Roof
- Extensive green roofs are in general not designed for active recreational use. They are developed mainly for aesthetic and ecological benefits. Distinguished for being low in installation cost, lightweight (50-150 kg/
) and with shallow mineral substrates, minimal maintenance is expected. Inspection should be preformed, at the minimum, once or twice a year. Plants selected are usually of low maintenance and are self-generative. Extensive systems can also be placed on pitched roofs of up to an inclination of 30°. They are common in European countries, especially Germany. - A roof or deck onto which vegetation is intentionally grown or habitats for wildlife are established, including extensive, intensive and semi intensive roofs; roof gardens; biodiverse roofs; brown roofs; public and private amenity spaces.
Drainage Facilities
Types of Drainage facilities
- Roof Drainage outlets
- Interior piping
- Gullies or scupper drains at doorways and parapet walls
- Gutters
- Spouts
- Emergency overflows
Drainage Outlet Installation
Roof drainage outlets in vegetated roof areas
- An inspection chamber, or a facility to enable inspection with ease of the outlet, should be installed over each outlet. This allows visual inspections to be conducted at any time and with ease; it helps to prevent contamination and stop plants from growing over & into the outlet thereby impeding the drainage of water through it.
- Choices of inspection chamber ranges from prefabricated metal and rigid plastic ones to those made from block work.
- Under no circumstances should the inspection chamber be a hindrance to drainage.
Roof drainage outlets in non-vegetated roof areas
- For roof drainage outlets that are located clearly away from vegetated areas, they should be covered by suitable gratings or perforated covers that are stable and durable, and effective in filtering out large particles and grains from entering the roof drainage systems via these outlets.
- In the event that the roof drainage outlets are clearly located away from vegetated areas and in a sunken location ( such as in a raised platform/ floor situation), there should be a sturdy, framed-cover above the outlet that is accessible and also flushed with the raised surface.
Emergency overflows
- Emergency overflows must not be hindered in any way (eg. edging, kerb, stumps, grilles, etc.) as they sought the emergency overflow discharge point.
- The immediate area surrounding the emergency overflow discharge point must possess the following characteristics:
- Free of vegetation, whether intentional planting or unintentional weeds.
Allow for instant visual inspection of the condition of the discharge point. Allow water to flow away freely and easily. Removal of water from pitched roofs Since use of gutters at the eaves of a pitched roof is discouraged in Singapore, there must be proper edging that is structurally stable to withstand the sliding force of the roof greenery as well as sufficiently pervious to drain away surface run-off and sub-surface drainage water. For steep roofs (with slope exceeding 25° to the horizontal), higher volumes of surface run-off and sub-surface drainage water should be expected, especially at the eaves. The use of overhanging or dangling vegetation, especially at the eaves, is highly discouraged.
Build-up Substrate should have:
- a depth in excess of 80mm
- a maximum of 20% organic matter
- Plants such as succulents retain water within their structure, reducing the risk of drying out
Irrigation
The more intensive the roof, the more likely it will require artificial irrigation system is required. Requirement for irrigation depends mainly on the following factors;
- The planting layer’s water demands
- Water storage capacity of the green roof configuration (e.g. growing medium, drainage layer)
- Local precipitation patterns
Rainfall is the typical source of water, however complimentary irrigation options include hoses, sprinklers, overhead irrigation and automated systems that pump from some reservoir storage. The establishment of a need for an irrigation system, and the design of an irrigation scheme, should be in accordance with the principles of BS 7562-3:1995 Planning, design and installation of irrigation schemes – Part 3: Guide to irrigation water requirements. Standards relevant to the design of specific irrigation systems include BS EN 15099-1:2007 – Irrigation techniques. Remote monitoring & control system, BS EN 15097:2006 – Irrigation techniques. Localized irrigation hydraulic evaluation and BS EN 13742-1:2004 – Irrigation techniques. Solid set sprinkler system – selection, design, planning & installation.
References
- CS E04:2010 Guidelines on filter, drainage and root penetration barrier layers for rooftop greenery
- The GRO Green Roof Code UK Green Roof Organisation (GRO) - a body facilitated by the National Federation of Roofing Contractors (NFRC)
