Designing a Green Roof for Low Maintenance

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With the arrival of the spring and summer months comes the mission of maintaining our landscapes.  That includes those that top our buildings – green roofs.

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Throughout North America, there are many beautiful, living roofs dotting our urban landscape that also require care. Not simply an aesthetic choice, some municipalities require rooftop maintenance. Toronto requires a maintenance plan in order to obtain a green roof permit. Washington, DC requires rooftop inspections twice a year. Many green roof system warranties are tied to performing maintenance and filing reports. Ultimately, maintenance keeps your green roof alive and well, looking good and performing as it should.

The extent of maintenance depends on the design, the plant selection, the depth of growing medium, the roof’s exposure and the weather. While it is hard to predict the weather, a designer can opt for a system with low maintenance features to reduce overall labor and cost.

Lightweight systems can achieve desired stormwater management goals and are easy to install, and retract (if necessary). Without additional growing medium, they invite fewer roof-damaging weeds and therefore require less manual labour.

Exploded 3D of XF301 Sedum Standard lightweight low maintenance system that do not require loose growing medium.

Exploded 3D of XF301 Sedum Standard lightweight low maintenance system that do not require loose growing medium.

The extensive 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 comparing to the photo on the right, an extensive system with 4″ of growing medium. The thicker green roof system is not only heavier: it is overrun by harmful and aggressive trees and requires significantly more maintenance at this point.

How to Design with Low Maintenance in Mind

Plant Selection
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” might be tolerated.

Irrigation Plan  
Access to water, with adequate pressure, close by the rooftop is critical for supplemental irrigation in the establishment phase and during periods of drought.

Fertilizing Plan
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 a nutrient supply on plants preparing to go into dormancy in the fall season.

Weed Control
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 and 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 the above, it is recommended to hire a professional green roof maintenance contractor with horticultural knowledge and “working at heights” training. Each visit and recent weather conditions should be recorded. Photos are needed for future reference and any potential warranty claims.