A2X Consulting

Definition

Green Roofs are rooftop gardens, a sustainable roofing alternative, planted on top of a waterproofing membrane. Green roofs provide excellent energy saving potential and storm water management. They can be used in industrial facilities, residences, office buildings and other commercial properties. They are aesthetically pleasing and highly functional.

Benefits of Green Roofs

Green roofs are an attractive roofing option as well as for maintaining ecological balance. They assimilate large amounts of rainwater thereby reducing the load on sewage systems. These gardens lessen air pollution, collect airborne particulates and store carbon. They insulate the building by keeping the interior cool in summer. With less solar energy reaching the roof substrate, the life of the roof is extended as the damage caused by UV radiation and daily temperature fluctuations is reduced.

Types of Green Roofs

There are two types intensive and extensive. Intensive green roofs have a soil depth of 8 inches to 4 feet. These are designed like a park with elaborate planting. They are planted over concrete roof decks to withstand weight requirements.

Extensive green roofs are lighter in weight. Their soil depth is 3 inches to 7 inches. Extensive green roofs are installed over various roof decks.

Cost versus long-term savings

It costs about $8 per square foot to build an extensive green roof. The traditional built-up roofs cost about $1.25 to $1.5 per square foot. The high up-front cost of green roofs is attributed to the cost of material and labor. As the demand rises the costs will likely decrease. However, the savings gained through green roofs in energy costs in summer, storm water infrastructure investment and extended life of the roof far exceed the up-front costs.

Green Roof Chicago’s City Hall

The 20,300 square foot semi-extensive green roof of City of Chicago has 20,000 herbaceous plants, 40 vines and two trees. The roof drinks 60% of the dirty rainwater. The green roof saves $5,000 a year on utility bills.

Reference

Heat Island Effect