IRRIGATION ON GREEN ROOFS

On 6 October 2015 at the Cities Alive green roof and wall annual conference, Michael Silver, New York City Commissioner for Parks and Recreation, announced that the city plans to have an additional 2.3 million m² of installed green roof by 2022.

Whether you are in New York, Berlin, or anywhere in between, green roof irrigation is a key component to ensure healthy, durable plant material. Even in wet and cooler climates, plant establishment and drought protection make irrigation a wise investment.

So now that we have established that irrigation is an important part of any green roof project, let’s explore the differences in irrigation equipment and application compared to a traditional system that you’d find on a corporate campus, sports field, or garden. 

SOIL

The main difference in irrigating a green roof over a traditional system is the soil. The green roof industry calls it ‘growing media.’ This growing media is specially formulated to be as lightweight as possible while having enough organic material to support plant life. To achieve this, growing media suppliers engineer the soils to be many times more porous than sand. So the challenge for green roof irrigators is to apply the water to the growing media as slowly and as uniformly as possible. Typical drip irrigation has been largely abandoned because of the rapid vertical movement of water through the soil. This leaves the green roof designer to choose one of the following irrigation methods to provide the best results for the project:   

IRRIGATION

Overhead Delivery

Water can be delivered overhead in the form of rotors or multi-stream, multi-trajectory (MSMT) nozzles such as Hunter Industries’ MP Rotator^®. These devices apply water much more slowly than traditional sprays (10-20 mm/hr) and are designed to cut through the wind that is common on rooftops. MSMT technology produces the most efficient overhead irrigation delivery option.

Below-grade Delivery

Because the growing media is so porous, providing irrigation below grade requires a mechanism for water to be moved horizontally. Fleece-based irrigation such as Hunter’s Eco-Mat^® does just that. It is installed just below the optimal root depth of the plant material, putting water where the plant material can use it, aiding in horizontal water movement, eliminating overspray, and providing additional water-holding capabilities for lightweight growing media. This method also allows the application of nutrients directly to the roots by means of a fertiliser injector. In the absence of a single system like Eco-Mat, subsurface installers rely on separate water-holding materials to keep moisture in the growing media. 

CONTROL AND ACCESSORIES

The brains of the irrigation system are the combination of controller and valve. Both can be powered by AC or battery (DC) and some can even use solar power. There is no difference in the valves or controllers used in green roofs or traditional systems. On larger projects, many irrigation professionals are able to connect the green roof valves to the main irrigation system controller. Advanced features like cycle and soak, which is present in many modern controllers, can assist with maximising water absorption in the lightweight growing media. 

Accessories help manage irrigation by providing the tools for maintenance and operation of the irrigation system. Weather-based, or 'smart' control, is today’s buzzword for efficient irrigation practices. Sensors should be added to a green roof system to provide onsite, weather-based, daily irrigation adjustment while providing rain and freeze shut-off protection just as they are used for landscapes on the ground. Remote controls make system tune-ups quick and easy.

Green roofs are designed to provide many public and private benefits and healthy plants are integral to the success of most. Regardless of the location and climate of your green roof, a well-designed, properly installed and maintained irrigation system efficiently provides the water necessary to keep plants healthy, delivering successful benefits for many years. ‘Earth-based’ irrigation professionals have all the tools and equipment they need to successfully irrigate a green roof. 

Todd Polderman is the Senior Marketing Manager at Hunter Industries and is a certified Green Roof Professional. For more information contact Hunter industries on 03 9562 9918 or visit www.hunterindustries.com