Your Five-Part Guide to Retrofitting a Green Roof or Roof Garden
The benefits of creating a green roof mean that as well as considering them for new buildings, plenty of architects and property managers look to retrofit them to existing buildings as part of ongoing maintenance.
The benefits include energy efficiency, mitigating the urban heat island effect, reducing runoff, increasing biodiversity in our urban areas and adding amenity space.
But before you start fitting and planting, here’s our five-part guide to what you need to consider.
A survey of buildings in Melbourne’s CBD revealed only 15% of commercial buildings were deemed suitable for retrofitting with green roof technology and only 3.1% were north facing, were not overshadowed and were physically suitable for green roofs. Factors to be taken into consideration include:
· position of the building
· orientation of the roof
· height above ground
· pitch (needs to be between 2% and 30%)
· weight limitations of the building
· preferred planting
· sustainability of components
· levels of maintenance
- Type of roof
There are two main types of green roof, intensive and extensive. Intensive roof systems are more costly because they include larger plants, heavy planters, water features and pathways which can add 200 to 1000kg/sq m to the load and will require safety measures such as railings and signage. Extensive systems often require little or no structural upgrade because they use lightweight growing mediums and smaller plants on a design weight of 50 to 200kg/sq m.
- Roof membrane condition
Although a green roof can protect the roof membrane from physical and climate damage, they should be installed only on roofs which are in good condition because repairs can be costly once the green roof system is installed. Green roof retrofitting is best carried out when current roofing systems are being replaced – otherwise ensure a professional roofing contractor carries out an assessment on the state of repair of the current system.
It’s absolutely vital that a retrofitted roof garden or green roof augments your building and doesn’t cause additional headaches. For this reason Jaydex uses the Novar WS-FLL Roof Garden waterproofing membrane system which incorporates anti-root reinforcement to protect the integrity of your roofing system. Contact Jaydex for more information on how the system can work for your retrofitting project.
- Planting system
Native plants are usually ideal for retrofitted roof gardens and green roofs because they have inbuilt resistance to disease, have proven performance in the climate and attract native birds and insects. Research carried out in New Zealand by Landcare on a green roof on the Waitakere Civic Centre also highlighted the need for:
· Visibility from the start of the project – therefore the use of upright tussock grasses and plants with contrasting colours.
· Weeding early in the project to reduce ongoing maintenance.
· The use of prostrate, low-branched plants which can withstand winds.
· The use of irrigation during summer to keep plants looking green and attractive.
· The inclusion of prolific seeders and spreaders to speed cover and recovery from drought.
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