Where would you rather stand barefoot on a hot summer day: a cool patch of grass or the parking lot of Wal-Mart? Ouch! That pavement is hot when the temperatures are cooking. It’s heating up everything under, above and around it as well.

The same thing happens to the surfaces of rooftops. They heat up under the sun's rays, increase the surrounding air temperature and heat up your home. Sure you’ve got insulation, but how much time do you spend in the attic during the summer?

By the time the heat gained from the sun reaches inside your attic you’ve lost your battle. It’s not your fault or your builder’s, after all we’re just tiny humans battling the tremendous heat energy of a very big star. You can of course crank up the AC, but that’s going to cost you money and contribute to increased outdoor air temperature.

Instead, consider that our little parking lot experiment has some valuable lessons that can be applied to your home’s energy-efficiency. What if, instead of dark asphalt, the roof was covered in vegetation?

It might seem far fetched but green roofs - roofs covered in vegetation - have been around for centuries and they are making a comeback in the United States. Green roofs have outgrown their “down-to-earth” reputation and are gaining mainstream momentum alongside the green building industry and the US Green Build Council’s LEED™ program.

The surge in implementation of this architectural element is due to an increasing awareness of how green roofs decrease energy loads (demand), reduce urban “heat island” effects, enhance climate, improve air quality and help alleviate stormwater runoff.

Germany has been a leader in green roof technology for over three decades. In this densely populated and developed country that struggles with annual river floods, green roofs help alleviate stormwater runoff. The country has over 100 million square feet of green roofs that absorb rainwater and restore natural hydrologic processes.

The history of green roofs predates modern German ingenuity. In early settlements in some of the world’s coldest climates, living roofs helped insulate homes. These early versions were seen throughout Scandinavian countries, the British Isles, Europe, the Aleutian Islands and the western plains of the United States.

The prevalence of living roofs in previous centuries was due to a scarcity of building materials but also the intrinsic insulating qualities of green roofs. Modern technology and materials replaced these earth derived elements, but the principles behind living roofs remain relevant, if not more so, today.

Solar gain and radiation are big challenges to heating and cooling efficiency in buildings. During the day, the sun’s energy is absorbed through walls and roofs heating the interior. At night, heat escapes through the building envelope by radiation and conduction. A green roof can moderate a building’s heat gain and loss, decreasing the energy load for both heating and cooling.

How? First, green roofs absorb the heat energy from the sun before it is absorbed into the building. The result is a more temperate surface that doesn’t transfer heat into the home’s interior and charge the air conditioning demand. In cold climates, the superior insulating qualities of green roofs help reduce heat loss.

I remember driving cross-country during the Chicago heat wave that caused hundreds of deaths. I was south of the city but still experienced some of the intense temperatures. In reaction to the unbearable heat that plagued the city in the 1990s, city officials embarked on a citywide cooling strategy that included green roofs.

The idea was simple – plants keep things cool. First, vegetation absorbs heat and moisture keeping the atmosphere cool and comfortable. Plants also give shade which helps prevent solar gain. These two qualities reduce roof temperatures, ambient outdoor temperature and the temperature inside the building.

The roof of Chicago City Hall is now an expanse of green with some 20,000 different species of plants. The project not only helps keep the surrounding air cool, it saves the city thousands of dollars per year in air conditioning costs. The same strategy is finding form in green roofs across the country on hospitals, parking garages, schools and other official buildings.

The energy saving green roof approach deployed in Chicago was based on simulation studies. Studies on the green roofs atop Chicago’s big buildings reveal that those structures can expect a 10% reduction in air-conditioning needs. In other studies, scientists have found that green roofs on smaller buildings can reduce solar heat gain by 95% and reduce cooling needs from 25 - 50%.

Most green roofs in the United States are on large-scale commercial or public buildings but the residential market is catching up. Green roofs can be installed on traditional residences providing homeowners with a beautiful way to cut down their heating and cooling costs.

Green roofs reduce energy costs by adding insulation in winter and absorbing heat in summer. In today’s housing market, energy savings equals increased property value. Plus, some green roof projects are eligible for tax credits and other “green” incentives.

Increasing demand for residential green roofs is creating opportunities for homeowners to implement this energy saving element, even with do-it-yourself applications. Architects, designers, engineers, contractors, suppliers, landscapers and garden nurseries are all starting to focus on residential green roof installations because of the potential energy savings and environmental benefits.

In residential construction, the integration of a green roof into the initial design allows a reduction in the size of the building’s HVAC system and reduces the amount of standard insulation needed. The tactic yields upfront savings as well as perennial energy savings in decreased electricity and fuel demand.

Green roofs can also be applied to existing roofs with the proper considerations as green roofs are an extension of the roofing system. The components include structural elements, insulation, waterproofing membrane, drainage system, filter membrane, growing medium and region appropriate vegetation. The systems can be either modular or “built-in-place”.

The type of green roof that is appropriate for your home, or office, depends on the building structure. The slope, condition and structural load capacity of the existing roof are all primary considerations. It’s also important to take into account the region, accessibility, water supply, drainage and exposure to sun and wind. All of these factors can be determined through professional consultation with an engineer, architect or contractor.

There are two basic types of green roofs: intensive and extensive. Intensive green roofs are often used as public open space, like the four rooftop gardens atop Rockefeller Center. They can be elaborate including vegetable gardens, ponds and in some cases even golf courses. Intensive green roofs require regular maintenance not unlike a ground level garden or yard.

Extensive green roofs are simpler, more meadow-like. They require less substrate, less maintenance and are meant to enhance building performance without much attendance other than basic care.

The cost of a green roof depends on the type of system (intensive or extensive), the size and whether it’s installed as an integrated part of initial construction or as a retrofit.

Extensive green roofs can be installed for as little as $10 per square foot while intensive systems start around $20 per square foot. Some companies have devised modular systems that allow owners to install most of the green roof themselves and eliminate some of the labor costs.

The initial investment needs to be weighed against several long-term cost saving factors. For instance, green roofs will increase the lifespan of roof membrane up to twice as long as conventional materials. The decreased maintenance and replacement costs are considerable.

The installation of a green roof in new construction will reduce the cost of HVAC systems, insulation and other materials. The decreased energy load on existing HVAC systems means they will operate more efficiently, require less maintenance, less fuel and less electricity. Both scenarios result in long term energy savings.

Costs, savings and benefits vary between roof systems and designs but green build consultants are available to help homeowners. Increased awareness, technology and specialized contractors are creating more opportunities for homeowners to install green roofs and reap the energy saving benefits.

Green Roofs Near You:

Rouge facility of Ford Motor Co. in Dearborn, Mich.

Rockefeller Center, New York City, NY

Chicago City Hall, Chicago, Illinois

Gap headquarters, San Bruno, California

Fairmount Waterfront Hotel, Vancouver

Hamilton Building, Portland, OR

Mountain Equipment Co-op, Toronto, ON

Green Roof Facts (from Green Grid Premier Roof Systems):

Tests have shown that green roofs can reduce indoor sound by as much as 10 decibels for every 3 inches of growth media.

Green roofs have consistently been proven to reduce heating and cooling costs by up to 25% and 50%, respectively, for the floor directly below the roof.

Urban heat island effect results in a 6 - 10 degree temperature increase within large cities.

A recent study by WESTON estimates that greening the rooftops of all buildings in the City of Chicago would result in nearly $100 million of annual energy savings.

*Note: The information in this article is general advice and not meant as a substitute for personal guidance from a financial advisor, real estate professional, general contractor or legal counsel. Although the author is a licensed realtor, the advice given in this article does not constitute any client contract or agreement between the author and the user. The author is not responsible for any losses, damages or claims that may result from your decisions.