Fact or Fiction: Green Roofs

By: Staff

4 Min Quiz

Image: refer to hsw

About This Quiz

Are green roofs easy or hard to maintain? Do they cost a lot? How much energy do they save, anyway? Test your knowledge in this "cool" quiz.

On a hot summer day, the surface of a traditional roof can be as much as 90 degrees Fahrenheit hotter than the surrounding air.

It's true! With their dark, non-reflective surfaces, standard rooftops are practically designed to trap light and heat.


Green roofs, also called "rooftop gardens," can only be installed on perfectly flat rooftops.

While a flat or low-sloped roof makes for easier installation and more roof-scaping options, a basic green roof can be added to almost any building, even one with a steep, shingled rooftop.


It costs more than twice as much to build a "cool" roof than to build a standard roof.

In many cases, the difference between cool and hot is all in the color. Fortunately, a reflective white or light-colored coating typically costs the same as the old heat-absorbing dark stuff.


An "intensive" rooftop garden, with deep soil and complex plantings, can absorb more than half of the rain that falls on its surface.

One of the many benefits of rooftop gardens is that they reduce stormwater runoff, absorbing an estimated 50 to 75 percent of rainwater.


The surface of a green roof can actually be cooler than the surrounding air temperature.

The plants on a green roof take in water through their roots and release it through their leaves, cooling the air around them.


A roof mist cooling system uses high-pressure hoses to spray a steady stream of water across a rooftop.

As its name implies, a roof mist cooling system uses just a fine mist -- less than 1 pint of water per square foot per day -- to cool rooftops through evaporation.


Once installed, a green roof requires no maintenance.

While the exact maintenance needs vary depending on the roof, rooftop gardens may need to be weeded, irrigated, fertilized, and replanted from time to time.


A ballasted roofing system uses rocks to keep the waterproof surface of the roof in place.

In addition to holding a watertight membrane down with their weight, the natural stones or pavers in a ballasted roofing system provide an insulating barrier against solar heat.


A 10-inch tubular skylight can be installed in an afternoon and illuminate about 100 square feet of living space.

Tubular skylights are inexpensive and easy to install. A 10-inch diameter tube can illuminate up to 100 square feet, and a 22-inch diameter tube can illuminate up to 600 square feet.


A cool roof can remain 50 to 60 degrees Fahrenheit cooler than a standard roof on a sunny day.

A cool roof is a roof designed to maintain a lower surface temperature in bright sunshine by reflecting more light and releasing more heat than a traditional roof.


Since green roofs are such a new concept, little is known about their sustainability or longevity.

Green rooftops and rooftop gardens have been around for thousands of years and can last twice as long as conventional roofs.


There is only one type of roofing product that meets Energy Star qualifications for cool roofs.

Many different kinds of roofing materials meet Energy Star requirements, which are based on a product's ability to reflect sunlight.


Metal is not an acceptable cool roofing material because it traps so much heat.

The reflective properties of painted and unpainted metal make it a good choice for steep-sloped roofs, but its tendency to retain heat limits its effectiveness for flat or low-sloped roofs.


White rooftops are generally the coolest and most reflective, but almost any color roof can be a cool roof.

Thanks to new pigments and special reflective coatings, "cool" tiles and shingles are available in a wide range of colors.


Rooftop gardens help to reduce greenhouse gas emissions.

Just like plants and trees on the ground, the vegetation in a rooftop garden reduces greenhouse gases by trapping and storing carbon.


Generally speaking, a green roof costs more to install than a cool roof.

A green roof costs anywhere from $10 - $25 per square foot, while a cool roof can be as inexpensive as 75 cents per square foot.


Urban Heat Island is the name of a new reality show where contestants test their endurance by performing feats of strength on a hot rooftop.

The urban heat island effect is the term used to describe the warmer temperatures in and around cities, due in part to the heat absorbed by rooftops and paved surfaces.


A green roof can help to reduce both cooling and heating bills.

In addition to absorbing heat from the sun, a green roof acts as an insulator, preventing indoor heat from escaping through the roof in the winter.


The rooftop garden on Chicago's City Hall covers 20,300 square feet (nearly an entire city block!) and features more than 20,000 plants.

This sprawling green roof saves the city $5,000 a year in utility bills and keeps summer rooftop temperatures 30 degrees cooler than surrounding buildings.


Over its lifetime, a green roof may actually be less expensive than a conventional roof.

A 2006 University of Michigan study found that a 21,000 square-foot green roof would cost $129,000 more to install than a conventional roof, but would save $200,000 over its lifetime, primarily in energy costs.


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