Green roofs are all the rage in urban areas around the globe. However, many don’t understand the constant need to maintain these roofs so they don’t become overgrown and potentially damage the very building they are a part of. Green roof maintenance doesn’t have to be difficult, but a plan must be developed.
Many jurisdictions, such as Toronto, Canada, are now requiring a maintenance plan to be submitted when getting a permit for a green roof. In Washington, DC, rooftop inspections are required twice a year. Many green roof systems require ongoing maintenance as a condition to maintain the warranty on their products.
Green roof design and plant species selection should take into account the maintenance requirements, both of the system being used, the plants, and the jurisdiction, if any. There are many systems available that require very little maintenance and are lightweight, something to be considered when engineering the building’s structure.
In the photos above, the green roof system on the left is a technologically advanced system using synthetic retention layers with no “loose” growing medium. It is lower in maintenance and lighter in weight when compared to the photo on the right, a system with 4″ of growing medium. The thicker green roof system is not only heavier, it is also overrun by harmful and aggressive trees and requires significantly more maintenance at this point.
Sasha Aguilera, Design Consultant for Xeroflor Canada, an industry leader in pre-vegetated roofing, has put together these suggestions for green roof maintenance and design:
Locally grown hardy and drought tolerant plants such as Sedum and mosses are ideal. Maintenance personnel should be familiar with green roof plants and the owner’s green roof aesthetic preference as some “weeds” may or may not be tolerated.
Access to water, with adequate pressure, close by the rooftop is critical for supplemental irrigation in the establishment phase and during periods of drought.
An annual application of slow release fertilizer, usually in spring, helps feed plants nutrients over a 3-9 month period. Care must be taken to avoid applying nutrients on plants preparing to go into dormancy in the fall season.
Weeding is necessary on all green roofs. Without proper maintenance, invasive weeds can overtake a green roof and pose a threat to the original green roof design. Woody plants can potentially harm the waterproofing membrane. A thin-layered system with synthetic water retention layers tends to be less inviting for harmful weeds than systems with thick growing medium. These thin-layered systems therefore require less routine, manual weeding.
Debris Removal and Drain Inspection
Inspection of the drainage paths is very important. Blocked drains and pooling water can cause root rot, and green roof plants may drown.
Document Your Visits
Once a properly installed extensive green roof is well established, its maintenance requirements are usually minimal. However, there should still be a person or team responsible for maintaining the system, performing visits 3 or 4 times a year. If the property does not have the personnel to do this, it is recommended to hire a professional green roof maintenance contractor with horticultural knowledge and training in working at height. A report should be written at each visit and recent weather conditions should be recorded. Photos are a must for future reference and any potential warranty claims.