Green Roofing

Dec 3, 2013

Today let us revisit green roofing or vegetated roofing.

A green roof is a roof with plants growing on it.

The plants are usually indigenous sedums which are extremely drought tolerant, though they can be a regular landscape with bushes and trees. Sometimes a green roof is planted with vegetables so that the building can provide food. The Brooklyn Grange Rooftop Farm #1 at Standard Motor Products is a 40000 sq.ft. green roof that provides New Yorkers with a bounty of fresh produce. That project was so successful that Brooklyn Grange Rooftop Farm #2 at Brooklyn Navy Yard, Building No. 3, a 65,000 SF farm was built.

Green roofs are somewhat expensive, nearly doubling the cost of a new roof, but since they shield the waterproof membrane from extremes of heat and cold and ultraviolet light, the roof membrane lasts longer. Roofing manufacturers double the warranty on the roof membrane if it is covered with a green roof by a certified installer. In addition to protecting the membrane, a green roof acts as insulation keeping the building warmer in winter and cooler in summer. The savings in the cost of membrane replacement in twenty or thirty years, along with the reduced energy use, means a green roof pays more than it costs in the long run.

In the heat of the summer the plants of a green roof keep cool by evaporating water so that on a hundred degree day the plants seldom get hotter than eighty degrees.

This cooling property of a green roof eliminates the heat island effect. The heat island effect is the reason that cities are hotter than the surrounding suburbs and countryside.

In addition to their cooling properties, a green roof absorbs water greatly reducing water runoff. There are special trays that can go under green roofing that will hold even more water. It is possible to store enough water under a green roof so that detention ponds are not required, which can allow more buildings to be built on a property. In this case the extra cost of a green roof actually pays dividends in increased buildable area for the property developer.

On some green roofs the soil is loose, sitting on top of a special drainage mat with landscaping fabric that allows water to run through and drain to the downspouts. On some green roofs there is a special wear layer that protects the membrane and pre planted trays are placed on the roof. The water runs through the trays and drains across the membrane like on a normal roof.

There are several buildings in the Lehigh Valley with green roofs. The Wildlands Conservancy Environmental Education Center building at the Poole Wildlife Sanctuary was built with a green roof, one of the first of its kind in our area. It is a green roof that everyone can easily see, as it is visible from the parking lot when you drive in.

The PPL Plaza Building in downtown Allentown has green roofs on the lower roof terraces but they are not visible from the ground.

The Lower Mount Bethel Township Visitors Center has a green roof that can be seen from the uphill side of the building.

The new STEPS building at Lehigh University has an 8,000-square-foot green roof.

With the success of green roofs in the area they are becoming more common.

The Arena Project being built in downtown Allentown is planning to include a 28,000-square-foot green roof.

The Hanover Township Municipal Building has a green roof.

The soon to be completed Forks Township Public Works Complex has been designed with a green roof.

The Nurture Nature Center in Easton has plans for a green roof

Further north the Tobyhanna Army Depot started with a 14,000 SF green roof pilot project in 2006 and now has 100,000 SF of green roofs.

If you go to the WDIY web site we have a link to information about the Tobyhanna Army Depot green roof pilot project and a link to the information about the Nurture Nature Center Project and the Brooklyn projects. 

Nurture Nature Center Project

Tobyhanna Army Depot green roof

The Brooklyn Grange Rooftop Farm #1

Brooklyn Grange Rooftop Farm #2 at Brooklyn Navy Yard, Building No. 3

(original air date 12/03/13)