Wednesday, November 14, 2007

If there's grass on the roof...

Green roofs, while conceptually and environmentally brilliant, have been plagued with something we are all to familiar with in the Midwest: weight.

In most cases, the majority of existing buildings have the space, but can't afford the load weight. Or often times, the building can afford to hold the roofing system, but would crumble under an additional moisture load. Such added weight is even a problem with on sloping roof systems.

" roofs can retain as much as fifty to seventy percent of water that falls onto a roof. Retention varies according to climate. Hutchinson et al reported that a 10 to 12 cm vegetated roof in Portland, Oregon retained 69% of the total rainfall with peak flow reductions of 80% during a 15-month monitoring period. Investigations in East Lansing, Michigan cdompared a gravel roof and a vegetated roof with the mean percent rainfall retention ranging from 48.7% for a gravel roof to 82.8% for a vegetated roof. A similar range was seen on two roofs of different slopes in Goldsboro, North Carolina. Total rainfall retention was 55% for the sloped roof and 63% for the flat roof. Peak flow was reduced by 57% for the sloped roof and 87% for the flat roof." WEBSITE

Poundage-be-damned, green roofing companies are finally beginning to recognize that the existing market is far more available than the future market, and have consequently begun to reduce the load weight in their systems. On company that caught my eye is GreenTech, a Roswell, Georgia based company that specializes in athletic fields, landscpaing systems, golf course systems, and yes, green roof systems.

They're no newcomer to the game, though. In addition to laying claim to New York's largest greenroof and the grass at Wimbledon, GreenTech has found a way to box out the weight and open up the lane to a lighter, newer, more accessible green roof.

From their website:

The GreenTech Roof Garden System weighs less than comparable systems for a couple reasons. Forklift and drainage channels displace soil with air. But more importantly, no drainage medium (gravel) is required in the system. This feature works to reduce weight of the system as well as cost of materials and labor.


So why is this system able to shed the pounds?

The system has built-in drainage channels that allow the water to flow through the soil into open channels and directly to roof drain outlets. At the same time, each high-density polyethylene module protects the roof surface from root infiltration and damage to the roof membrane. The result is a large planting surface -- with the all-important root depth -- that's more lightweight and flexible than other green roofs. Given the fact that it still discharges the water, some might view the system as less than substantial as other systems, but it needs to be kept in mind that the grey water discharge can be stored for landscape use.

Additionally, the GreenTech allows for almost 40 times the drainage and air flow capacity of conventional drainage systems. Even the drainage channels displace soil, resulting in a 20 to 40% weight reduction. You can even remove the individual sections to replace, repair, or modify the existing system.

But this is what I like most:

The system can be installed in very unlikely places. A back patio loft in the city can suddenly transform into a mini Central Park. You drop the crates, fill with dirt, cover with sod, and finish the edge (simplified, yes, but it is undoubtedly FAR MORE basic than most systems on the market). I like.