Geotextile Applications

Geotextiles play an important role in building green roofs. The modern green roof concept was developed in Germany over 50 years ago. Many European cities have been mandating green roofs for over 30 years. However, they date back considerably further: The Vikings used turf roofs centuries ago.

But, green roofs are a relatively new phenomenon in the U.S. The first Green Roof for Healthy Cities (CRHC) conference took place in Chicago in 2003. But it is a fast-growing market, beating even the most optimistic growth estimates from 2004-2007. A Michigan State University study found that the area covered by green roofs increased 80 percent in 2006 compared to the year before. The current estimate is 7 million SF to be installed in 2010.

The New York City High Line on Manhattan's West Side is one of the most stunning examples of utilizing green roof concepts to revitalize a 19th Century structure and create a 21st Century plaza and urban promenade. Its linear roof garden offers a sophisticated planting and drainage plan that is beautiful, useful and green! 

• Centuries Old Concept
• Increasingly Popular
• Absorbs Storm Water
• Insulates
• Reduces Noise
• A Garden on Your Roof!
• Last 3 Times Longer
• Earn LEED credits!

What Are Green Roofs?

Green roofs are simply gardens on your roof. They can be a simple layer of turf or a complicated and beautiful hanging garden. But green roofs are more than just beautiful. They absorb storm water and heat, reduce noise pollution and add an extra layer of insulation to buildings. In fact, they can cut cooling costs in half. However, many building codes require an insulation layer such as polystyrene.

And while green roofs may cost as much as twice that of a conventional roof, studies show they last three times longer. And many green roofs are part of the Leadership in Energy & Environmental Design (LEED) green building rating system and therefor can help earn LEED credits

There are four basic components to a green roof system:

Waterproofing

This is the most important component of a green roof, or any roof for that matter. The waterproofing membrane must be completely leak-free. In the geosynthetic industry, geomembranes are known to have a few leaks per acre installed. The roofing industry uses 3 types of membranes: thermoset, thermoplastic and modified bitumen. This type of waterproofing may consist of a single-ply sheet membrane, or a system consisting of multiple layers.

Liquid applied membranes, including polyurethane and polymeric materials, can reduce labor costs, reduce mechanical transitions and result in an excellent seal because the material easily spreads in difficult to reach areas and around structures such as HVAC and roof-top lighting.

Root Barrier

Membranes that are not root-resistant, such as bituminous-based membranes, require a root barrier. These root barriers are typically thermoplastic sheets laid on top of the finished waterproofing or a liquid applied polyurethane imbedded into the surface. As such, thermoplastic membranes and many polyurethane spray on liners are inherently root resistant and do not require a root barrier.

Insulation

Green roofs effectively absorb heat, cool roof surfaces and stabilize temps at the freezing point. But this is a seasonal phenomenon and thus varies. They offer minimal thermal insulation. As such, many building codes require an insulation layer such as polystyrene for installation above the waterproofing membrane and polyisocyanurate under the membrane.

Water Management

A green roof system must provide water drainage, filtration, retention and aeration. A geonet is one way of achieving good drainage and aeration. A lightweight nonwoven geotextile provides the filtration element. Geonets can be purchased with a nonwoven geotextile bonded to them.

Stabilizing a Green Roof

For roof slopes exceeding a few degrees, a reinforcement material may be required to prevent downward sliding.  Cellular confinement such as US Fabric's Envirogrid® offers flexibility in achieving this goal. Next time you are at the new Washington Nationals Park, check out the batter's eye in center field. Envirogrid® is reinforcing the vegetation in this unique architectural feature!

J-Drain Greenroof (GRS)

In addition to most of the individual components of a green roof system, US Fabrics offers J-Drain GRS for your green roof drainage application. GRS is an "all-in-one" green roof product. J-DRain GRS is a pre-assembled drainage composite consisting of a high-strength dimpled core with a layer of geotextile filter fabric/protection media attached top and bottom. The dimples in the core create chambers that store some of the excess rainwater while allowing most to pass through into the roof's collection system. The top geotextile filter fabric allows excess water to pass, while holding the planting media in place as a root barrier. The bottom layer of geotextile fabric acts as a protection media for the roofing membrane.