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Green roofs are gorgeously green in colour, not just in name. The term refers to gardens which are planted atop houses, office buildings, and many other structures for a whole slew of environmentally friendly reasons. They form a protective layer that lowers the total cost of energy needed to heat and cool the building below. Roof gardens also act as an air filter, removing and storing pollution and greenhouse gas emissions. Perhaps most important, they add a touch of natural beauty to the landscape, especially important in the midst of a jungle or urban high rises.
There are two types. Extensive green roofs are basically a light 2″ tall cover of shallow-rooted, hardy alpine plants such as sedums, which require low maintenance not no maintenance. Intensive green roofs feature a wide variety of vegetation, and are more maintenance-intensive. How do you maintain a green roof garden? Here’s what you need to take care of.
Feeding and Watering
A green roof is essentially a giant container garden, planted in a relatively shallow layer of soil to reduce weight on the roof. Due to the limited amount of nutrients available to the garden via the soil, you may need to apply a slow-release fertilizer. Once the plantings are well established, an extensive green roof may not require any water apart from natural precipitation. Intensive green roofs, on the other hand, usually must have an additional water supply. (This is especially true on a roof with a steep pitch that allows storm water to run off more quickly.) The easiest way to provide this is with a drip irrigation system, which has the added benefit of increasing evaporative cooling. Under extremely hot, dry conditions, you may need to supplement with hand watering or an overhead spray.
Weeding and Trimming
Although less susceptible to weeds than its earthbound counterpart, a green roof will require regular weeding in the early stages, tapering off as it matures. Be sure to remove weeds before they go to seed, in order to minimize spreading. The thin layer of soil will tend to encourage horizontal, rather than vertical, growth; as a result, you won’t need to mow or trim the garden as frequently as a conventional one. However, a certain amount of pruning and clipping will still be required to keep the plantings healthy and good-looking.
With every green roof, a waterproofing membrane must be installed to protect the roof material and the building underneath. Test the membrane for leaks by flooding it with water prior to planting. There are a number of membrane materials on the market. Ask your landscape architect to recommend one that is highly root resistant. Continue to inspect the membrane on a routine schedule in order to detect any leakage or drainage backup.
The abundant food, water, and shelter offered by a roof garden make it appealing not only to human beings but also to animal and insect pests. Inspect the garden regularly for signs of infestation such as chewed-up plants, burrows or nests, and droppings. Remove decaying vegetation that may attract ants, as well as stagnant water — a potential mosquito breeding ground. Decrease the pace of drip irrigation to deter moisture-loving snails and slugs. Deter pigeons with anti-roosting devices. You may need to call in pest control professionals to get rid of a persistent infestation such as squirrels or rats; ask them to use no-kill traps.
If a green roof is allowed to dry out excessively, it is likely to become a fire hazard. Danger can be avoided by:
• Installing a drip irrigation system, possibly hooked up to a fire alarm.
• Planting fire-resistant succulents, which do not tend to dry out, even in hot weather
• Using a growing medium that contains a high percentage of inorganic material, like perlite or sand
ALL roofs require some level of maintenance. We recommend a biannual preventative maintenance package
This addresses any weed growth resulting from windblown seed/animal deposits, clears drainage channels and stone borders to ensure the roof is free draining and is functioning as it should. This helps prevent against expensive roof replacements which can be a result of deep rooting invasive species such as buddleia/tree saplings causing damage to the roof membrane. Fire risks need to be considered – irrigation particularly on Wildflower roofs/biodiverse roofs to prevent vegetation drying out especially in periods of prolonged drought. It is important maintenance is a key consideration when purchasing/installing a green roof. Whether this is maintenance that is safe for the client to complete themselves or the additional costs in procuring an external service to complete the required green roof maintenance [such as that which is offered by Sky Garden]. It is important when maintaining green roofs/working at height that all relevant health and safety is considered – for example it is much better to install a man safe system/fall arrest point as part of the initial build as oppose to at a later date where is can compromise the integrity of the roof membrane.