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Architecture & Urbanism

Nassau Ice House, Green Roofs
 

Nassau Ice House Lofts
1024 Dean Street Brooklyn, New York

Two different roof tops comprise the 2300 square feet of green roof space at the Nassau Ice House. The top terrace roof, which is accessible from one of the apartments, has unobstructed southern lighting. It is 900 square feet with a 4 inch deep substrate. The first layer is the waterproof membrane, which protects the roof from erosion and possible leakage problems. The drainage layer is made from a Barrett's Ram Roofscape 1241 Drainage/ Retention Mat; 16 millimeter high density polyethylene film and a 60 psi Dow Styrofoam Plazamate. The next layer, the substrate is comprised of a mix of 70% expanded shale, which is lightweight and porous, 15% sand and 15% compost. The plant selection is mostly sedums, succulents and small herbs. The selection includes chives, lavendar, blue spruce, bailey's gold, white spurium, fameflower, dragon's blood and russian stonecrop. The costs on this roof from consulting and design to materials and installation totals $13.96 per square foot. The costs of roofing istelf, comprises most of that cost at $8.33, making the addition of green roof features only about $5.63.

The second green roof is a 1400 square foot wood truss roof. It is 20 feet off the ground enabling the passengers on the elevated subway train to view the roof. A Sarnafil PVC membrane was used not only for waterproofing but to act as a root barrier as well. Although this eliminated the need for a separate root barrier, it is more costly. The drainage layer is a Mirafi N-Series Non-woven Polypropylene geotextile, which is all that is needed for adequate drainage because of the slope. The substrate layer is only 2 inches deep and is comprised of 70% expanded gray shale, 15% compost and 15% sand. The roof has a 17 degree slope and a wood grid of L18"xW24"xH1.5" boxes was constructed to allow the plants adequate maturation time and to prevent substrate loss. The original wooden truss needed steel reinforcement to increase the roof's load-bearing capacity as a result of the extra 14 pounds the green roof added fully saturated. Sedums and succulents were planted on this roof due to their ability to survive in only 2 inches of substrate. The succulents were primarily places at the top, where conditions are the most arid. The total costs of this roof were $16.30 per square foot. Standard roofing costs amounted to $12.65, making the cost of the additional green roofing $3.65 per square foot. The developers recommend using pre-mixed substrate, pre-washed stones and a cheaper membrane to act as a root barrier, to cut costs even futher.

 


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