Green Roofs – Efficient Design Starts At The Top

Green roofs have seen a surge in popularity recently as sustainable building designs become more mainstream. Soil and plantings on a building’s rooftop can help manage water runoff, improve air quality, and reduce energy use by moderating indoor temperatures. They can also prolong the life of a building’s roof by protecting it from the wear and tear of wind, water, and UV rays. But a truly efficient green roof requires a dedicated design to ensure proper drainage and healthy vegetation without compromising the underlying roof structure, as well as a growing medium that is more stable and lightweight than normal soil.

Green roofs can be modular systems (typically arrays of trays containing all the vegetation and necessary drainage structures), or they may be permanent designs grown directly on the rooftop. Designs can be either “extensive” (thin and lightweight layers of plantings focusing on function over aesthetics) or “intensive” (more substantial landscapings or roof gardens, usually involving thicker layers of growing medium up to 12” deep).

Here is a look at some features and advantages of three popular types of systems currently on the market.

Xero Flor Green Roof System

Xero Flor Green Roof

3,500 SqFt. Xero Flor Green Roof at Michigan State University (image: Xero Flor)

A green roof isn’t quite as simple as merely rolling out some sod, but the Xero Flor system comes close. An impermeable base layer is installed first to protect the rooftop, then a layer of nylon filaments is added on top of the base layer to allow drainage and water flow. A fleece fabric layer comes next to retain water for the plantings, and finally a layer of Xero Terr growing medium for the pre-vegetated sedum and moss mats that are rolled out on top.

Minimal thickness designs mean only certain hardy plantings can thrive, and any continuous system like this can make it difficult to access the roof below if repairs are needed. But a functional system like Xero Flor provides all the benefits of a green roof without adding unnecessary weight to the roof structure, even when it’s fully saturated.

More details are available at the Xero Flor website.

GreenGrid Green Roof System

GreenGrid Green Roof System By Weston Solutions

GreenGrid Green Roof System (image: Weston Solutions, Inc.)

A modular design like the Weston GreenGrid system offers added flexibility and convenience to a green roof. Pre-planted trays are available in thicknesses ranging from 2.5” to 8”, depending on foliage choice and weight limitations. As long as the building’s structure can support the added weight, the modules can be placed directly on a roof’s existing membrane.

The trays are constructed of UV-resistant recycled plastic, and they can be easily moved or rearranged to accommodate roof repairs or design changes. However, modular designs may not be considered as aesthetically attractive as permanent plantings, and the individual trays of some systems may not be able to handle drainage quite as effectively as continuous systems.

You can find the GreenGrid Roofs website here.

LiveRoof Green Roof System

LiveRoof Green Roof System

LiveRoof Green Roof System (image: LiveRoof, LLC)

LiveRoof LLC has developed a hybrid system that offers the convenience and flexibility of a modular system with the complete coverage of a whole-roof design. Pre-vegetated modules are transported to the job site with removable edging; once the modules are fitted together, the edging is removed to create a continuous layer of soil. Although this system isn’t quite as flexible as self-contained trays once it’s installed, sections can still be removed for roof access if necessary. The continuous layer of plantings allows for drainage and root growth, and also provides gap-free insulation for the roof.

Learn more at the LiveRoof website.

Do you have firsthand experience with these (or any other) green roof systems? Leave a comment below and let us know!

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