Notes from our green roof field trip
We really enjoyed last Friday’s tour of the green roof atop the Parks Department’s Five Borough Technical Services Complex. The roof is gorgeous and inspiring, and it’s worth checking out our flickr photos (and videos) of the tour if you weren’t able to make it. At over 15,000 sq ft, this is the fourth largest green roof in the City and the only one we know of in the country that compares so many different green roof technologies and configurations. Chief of Technical Services Artie Rollins graciously walked us through the 16 different systems currently in place; he and his staff are always experimenting with new soil types, plant species, layouts and supporting layers. Right now they use tray systems, pre-vegetated modular systems, cedar planter boxes, overhead trellises, elevated planters and a green wall. A few notable tidbits we picked up:
- Soil is heavy! (Soil that weighs 14 lbs/sq ft when dry is 25 lbs/sq ft when wet.) Weight is a big factor in determining what soil to use on the roof. Five Borough’s roof and outdoor atrium use various combinations of Gaia Soil (of which the main ingredient is a non-toxic recycled expanded polystyrene foam), Metro-Mix and mineral soil, all of which have different compositions, weights and benefits.
- The native plant mix is more effective at evapotranspiration than the non-native plants, so that patch of the roof measures about 10 degrees cooler than other areas on hot days.
- Now having proven the benefit of their green roof systems in energy savings and roof lifespan extension, the folks at Five Borough are looking to branch out to other Parks sites. They’ve identified a number of Recreation Centers around the city that meet necessary specifications for green roof installation and are hoping to proceed within the next year.