If you don't know that New York City's 22,000 acres of dark, heat-absorbing rooftops play an equally dark role in the urban heat island effect--a phenomenon in which local temps rise 6 to 22 degrees above surrounding areas--then you probably also don't know the difference between a 'cool' roof and a 'green' one.
Fortunately, the October issue of Habitat Magazine offers a handy fall-is-the-time-to-plan primer as well as pricing info for the two main options for making your roof environmentally responsible.
The article is not yet available online (Update 11/11/11: Now it is - click here), so here are the basics:
A "cool roof" sports a light-colored surface that reflects sunlight instead of absorbing it. The surface is basically paint that costs 25-50 cents per square foot and can be easily applied by your super. (It works on asphalt roofs but not gravel.) For more info, check out the city's Cool Roofs Program.
A "green roof" is actually alive. It's "essentially a layer of vegetation growing in a light-weight, soil-like medium." The lite-version of a green roof, referred to as "extensive," has a light layer of vegetation and is the most common. The "intensive" version has enough soil for shrubs and maybe even trees and needs more maintenance. Green roofs cost around $20-$30 per square foot to install, which can be partially offset by a $4.50 per square foot property tax abatement. Tip: To keep your green roof growing, don't let the super do the weeding unless he knows what a weed looks like.
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