Does your client want a green roof? Read this first!
Don’t underestimate the maintenance requirements for green roofs
By John Bleasby
Incorporating a ‘Green Roof’ into a new house or extension is very topical today in discussions between architects, contractors and homeowners.
However, no one should be under the illusion that a vegetated roof is a simple matter that can be forgotten after installation. If a homeowner wants low-maintenance, they should go with traditional hard roof materials.
A Green Roof is a living thing. Consequently, there are a host of issues that accompany and extend beyond the design stage that factor into the success and long term viability of the roof beyond the mere structure itself. Without thorough consideration, there can be serious problems.
- Green roofs need to be weeded. What is a weed? Just like in the garden, a weed is anything that is unintended, invasive and potentially damaging to the roof membrane. The larger the root structure of the weed, for example small trees like sumac or poplar, the bigger the issue. Given the exposure of most roofs, one should never be surprised what errant seed can potentially land and take hold.
- Green roofs need fertilization. There are choices to be made between slow release products applied annually versus liquids or low nutrient types that need more regular application. Since properly designed green roofs have drainage systems, fertilizer run off may further dictate product choice based on the system and roof slope.
- Green roofs need water. Most roofs are heavily exposed to the sun and wind, which means they will dry out more quickly than a garden patch shaded by trees or other buildings. Therefore they need water. Of course, plant choice must follow regional climatic conditions; and even afterwards, irrigation will be needed.
- Green roofs need to be kept clean. There’s little difference between the general maintenance of a vegetated roof and that of a lawn or garden. Autumn leaves, trimming, even air-borne garbage like coffee cups need to be dealt with.
A Green Roof requires relatively easy access.
Green Roof maintenance requires planning for access points onto the roof, plus pathways around and through the vegetated sections. But there’s more: The question also arises, “Who will do the actual maintenance?” Will it be a professional crew that arrives with ladders, safety harnesses and the correct equipment on a scheduled basis? Or is the homeowner expected to climb ladders or perhaps access the roof area by stepping through an opening window in a bedroom? Some maintenance activities, such as plant thinning and pruning are annual or semi-annual. Others activities like weeding or cleanup may require regular access.
Related to this is the irrigation system. Unless the home is located in an area of regular and reliable precipitation (a rare thing these days) an irrigation system will be needed, which in turns requires its own maintenance, not the least of which is the shut-down and re-opening at each end the growing season. At the same time, vegetated roofs located in areas of low ventilation can, if not properly ventilated, can become stagnant and prone to plant health issues and fungal diseases.
Look before leaping
This is by no means a comprehensive outline of the issues, however, it should be clear that maintenance and proper design go hand in hand from the outset, and must remain part of the homeowner’s property management process. Don’t let your client rush into a Green Roof commitment without understanding exactly how big a commitment is really required.
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