ECO-FRIENDLY ROOFS, P.2

At the headquarters of the social-service organization Common Ground, at Brook Avenue and 148th Street in the South Bronx, a green roof — safely enclosed by a high chain-link fence, with minimal walkways and a few benches — offers is both an environmentally responsible creation and a peaceful retreat.

So, with all these benefits, why aren't green roofs more common? According to Don Sussman of the landscape company Town and Gardens, which has designed and constructed green roofs for the Diane Von Furstenburg Headquarters (pictured, previous page) among other venues (disclosure alert: and with whom I've worked on several green-roof projects), cost is an undeniable factor. The typical price is $20 to $30 per square foot of vegetative area, and installing materials also tends to be costly. A $4.50-per-square-foot property-tax abatement helps, but hiring an engineer or architect to file with the Department of Buildings can eat into those savings.

Think Before You Plant

Sussman cautions a co-op or condo board to consider its goals carefully before installing a green roof. Generally, a vegetative roof does not work well if a board primarily wants an amenity. A complete green roof is not intended for frequent traffic, only for weed-pulling and other maintenance.

Josie Rivera, who maintains her co-op's green roof at 1347 Bristow Street in The Bronx, reports that she keeps a lock on the roof door [Editor's note: which appears to be a fire hazard and possibly a fire-code violation] and goes up only once or twice a week to pick weeds — although, she admits, "Sometimes I do bring a book." Make sure whoever's weeding knows what is actually a weed — sometimes supers and residents pull up plants that had been placed only months before.

If a board does opt for a green roof, it's best to call on experienced designers and contractors. One critical concern: the load-carrying capacity of the roof. According to Sussman, "Saturated growth medium weighs as much as a layer of concrete of the same thickness — around 25 pounds per square foot for four inches." In order to meet code, any building should be able to handle that weight, but poor roof installation or maintenance can result in reduced capacity, especially when the supporting structure is wood. So inspect your roof's structural condition before going ahead.

Examine the roof membrane for leaks. Sussman strongly recommends you go the extra mile and install a detection system that will enable any membrane leak to be pinpointed within millimeters.

The Blue Roof

Every New Yorker notices that rainstorms tax our sewer system. But lakes at crosswalks are just the beginning. When a large amount of rainwater enters the sewers, our sewage-treatment plants can be overwhelmed, causing them to release untreated sewage straight into our rivers. Known as Combined Sewer Overflows, or CSOs, these discharges amount to an astounding 27 billion gallons each year.

A blue roof alleviates CSOs in much the same way a green roof does, by retaining water during a heavy rain. But instead of vegetation absorbing the moisture, a special roof drain goes to work, restricting the flow rate. After a rainfall, when water pools on a roof, controlled flow devices allow a steady, slow stream to enter the sewers over many hours, rather than as an intense surge all at once.

A blue roof costs considerably less than a green roof. Figure around $5 per square foot for a second membrane (highly recommended) and labor.

Any of these roofs — white, green or blue — would make a beneficial contribution to our urban environment. Indeed, the opportunity to improve our roofs would seem obvious. Yet when "roof" comes up on the agenda, many boards find themselves almost paralyzed. The safest choice often seems to be "keep doing whatever we did the last time."

This paralysis is understandable: The stakes can seem impossibly high. After all, a reliable roof is critical to the integrity of a building. But the possibilities can be both affordable and beneficial — for a building and for this invaluable urban environment we all share.

Photo courtesy Town and Gardens

For articles going back to 2002, join our Archive >>