CO-OP CONDO COOL ROOFS, GREEN ROOFS

Easy Option: The Cool Roof

One of the easiest and least expensive ways to make an urban roof environmentally responsible is to turn it into a "cool roof." During this past summer's record-setting heat wave, New Yorkers experienced something known as the "urban heat island effect." Simply put, the temperatures we experience during the day are around 6 degrees hotter than those in surrounding areas, and at night can be as much as 22 degrees warmer. The cause? Our abundance of dark, impervious surfaces such as roofs and pavement, which tend to warm the air, and a lack of vegetated areas, which ordinarily would cool the air.

The results are not pretty: more demand for energy to keep us comfortable, higher electric bills, and a rise in air pollution and greenhouse gas emissions.

A cool roof — also known as a white, or reflective, roof — has a light-colored surface that reflects sunlight instead of absorbing it. By minimizing that absorption, the cool roof has a lower temperature than a typical roof on a sunny day and contributes less heat to the atmosphere, diminishing the urban heat island effect.

For just this reason, over the past two summers the mayor's New York City Cool Roofs Program has covered more than two million square feet of the city's rooftops with a reflective coating. The program's website offers a "Cool It Yourself Kit," with information about measuring your roof, navigating roof warranty issues, and selecting and applying the right reflective coating.

Most coatings cost from 25 to 50 cents per square foot, and a super can easily apply the paint on a small rooftop. As with any flat roof, of course, a cool roof will accumulate grit over time, but an annual cleaning will keep the cool roof doing its job. Options range from silvery coatings that reflect around 60 percent of the sunlight (but begin to wear off after around five years) to slightly more expensive elastomeric coatings, which reflect over 90 percent when new and will usually last seven to 10 years.

If your co-op or condo is replacing a roof — an expensive but sometimes necessary event — you can install an intrinsically reflective roof membrane, which requires no coating. Is your building considering a rooftop patio? Reflective roof pavers are also available.

A cool roof, in fact, significantly extends the life of the roof membrane. A cool roof will also transmit less heat to the top floor of a building, and if this space is air-conditioned, installing a cool roof will usually result in energy savings on hot summer days.

Remember, though, that nothing improves energy efficiency like roof insulation, which a surprisingly large percentage of older apartment buildings do not possess. Roof insulation is fairly easy to install and relatively inexpensive.

The Green Roof

A green roof has a layer of vegetation growing in a lightweight, soil-like medium, which is installed over the roof membrane. There are two types: "extensive," the most common, with a carpet of short sedums; an "intensive," with enough soil for shrubs or even trees.

Most green roofs also include additional components separating the roof membrane and the growing medium, such as a drainage layer to drain excess water and a root barrier to prevent any aggressive plants from damaging the membrane. Like a giant sponge, a green roof will absorb rain rather than allow it to flow unimpeded into the sewer system. The greenery absorbs some of the water, and the rest evaporates.

Next page: Real-life Examples and Blue Roofs >>