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The New Jersey State House is located at 125 West State Street, Trenton, NJ, 08625; visit the New Jersey Legislature website. Read the entire case study from Colbond, and learn about Colbond in The Greenroof Directory.

The New Jersey State House is located in Trenton and is the house of government for the state of New Jersey, and it boasts a 175,000 sf Plaza Deck/Roof Garden located over the parking deck. The original construction of a plaza on top of the 4.2 acre parking garage was topped with ten inches of crushed stone ? no trees, no grass, and no pavement, just a stone area for local residents to walk their dogs. Many residents were unhappy with the lack of aesthetic appeal. To top it all off, the plaza leaked because it had been built without a protection layer between the roofing / waterproofing membrane and the aggregate layer.

When the general contractor for the reconstruction project was named, the scope of the work had not yet been established. The original waterproofing membrane manufacturer was brought back in and asked to recommend some corrective measures.

The reconstruction design incorporated two separate layers of drainage material. One drainage course was placed between a new concrete topping slab and a soft, rubberized asphalt membrane. Enkadrain 9812 was the subsurface drainage composite chosen for this layer because of its performance characteristics and the protection fabric on the second side.

The second drainage layer was placed directly on top of the new slab and right below two feet of soil and stone. This drainage layer was also quite important since any water that would fall on the deck must have an evacuation path. With a solid concrete parking structure below, the additional weight of the soil was not an issue. The concrete was poured, troweled smooth, and Enkadrain 9615 was placed directly on top of it, then covered with the stone and growing media.


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