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The green roof advantage

September 19, 2010
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As the environmental movement becomes more mainstream, a growing number of building owners and managers are choosing to incorporate green building elements into their properties.

Just as driving a hybrid car and installing energy-saving light bulbs often makes both monetary and environmental sense, choosing a green roof is becoming a smart financial decision.

One of green roofing’s strongest financial benefits is that it provides superior insulation, which helps to reduce skyrocketing energy costs.

The Energy Information Administration, in their August report, predicted that prices for heating oil and natural gas will continue to climb.

Heating oil prices during the upcoming winter are projected to average $4.34 per gallon, an increase of about 31 percent.

Natural gas prices are projected to increase about 22 percent from last year’s prices.

Another financial incentive to installing a green roof is tax breaks.

As of August 2008, at least eight states and 22 localities have endorsed green policies.

While some of these locations simply require that new government buildings be constructed inline with U.S. Green Building Council’s (USGBC) Leadership in Energy and Environmental Design (LEED) standards, others give tax breaks and expedited permits to green buildings.

A few policies, such as one in Maryland’s Baltimore County, give tax credits to builders for green construction.

While installing a green roof alone may not make a building eligible for tax breaks, it will qualify the building for significant points through the LEED system.

What is a green roof?
Green roofs are often defined as a roofing system that is topped with vegetation.

Although this definition does not tell the whole story, planted roofs do have numerous environmental benefits.

They reduce stormwater runoff and may decrease energy consumption.

Planted roofs absorb stormwater, a major benefit in cities where the water washes into — and therefore pollutes — nearby bodies of water.

Numerous municipalities across the U.S. are either considering or have already instituted a charge to tax excessive stormwater runoff in an effort to pay for water treatment programs.

However, buildings with green roofs are often exempt from the tax or qualify for a reduced rate.

This is because a green roof with 2.5-inch deep soil retains, in general, about 67 percent of rainwater.

During a major rainstorm, which generates about 1.25 gallons of water per square foot, the roof will absorb approximately one half-gallon of water per square foot, or 40 percent of it.

Vegetation on the roof also helps stabilize the temperature of the roof, lowering cooling bills.

For example, on a 90 degree day, a conventional black roof is about 170 degrees Fahrenheit, while a reflective white roof will range between 110-120 degrees Fahrenheit.

In comparison, a vegetative roof will actually be a little a cooler than the temperature outside.

The new green roof
Despite the environmental advantages that vegetative green roofs bring, at an extra $10 to $20 per square foot, this style of green roof can exceed the budgets of many property owners.

A roof does not necessarily need to sprout grass and bushes to be considered green; the following innovations qualify for LEED points, cut down on energy bills, and are considered green due to recycled content and sustainability.

A coal tar-based, self-adhered membrane has all the benefits of a coal tar pitch roof without the negative environmental and health issues.

It outlasts standard roofing membranes by up to 30 years and is fully recyclable.

The vast majority of roofs are installed using a technique called “hot mopping,” which, in heating up tar, emits toxic fumes known as volatile organic compounds (VOCs).

The method does not comply with current EPA regulations.

Other systems utilize a “peel and stick” membrane that peels, but does not stick.

The self-adhered coal tar membrane forms a structural bond with the substrate and is water tight instantly.

Another new innovation in environmentally-friendly roofing is superior insulation.

The majority of roofs use the traditional polyisocyanurate (ISO) insulation, which quickly loses its R value, or ability to retain heat.

In fact, the R-value of ISO insulation cannot be guaranteed for any length of time, resulting in heat loss and increased energy consumption.

A properly designed green roof will employ an extruded polystyrene (XPS) insulation that is guaranteed by the manufacturer to hold 85 percent of its R value for 30 years.

This allows building owners and managers to calculate their energy-savings for decades to come.

Before you buy
Like much of the green building movement, the roofing field is subject to much “greenwashing.”

Ever since green became a hot marketing buzz word, every roofing installer and manufacturer has scrambled to add a green roof to their offerings.

This means that the field is awash in products, many of which provide little environment benefit.

While the U.S. Green Building Council publishes LEED guidelines that can help property owners and managers determine which building elements are actually environmentally friendly, it’s difficult for the organization to stay constantly on top of all the changes in the construction industry.

The USGBC is planning to introduce a new generation of design standards early next year which will include specifications for the latest developments in roofing design.

In the meantime, consumers have to do much of their own research in order to determine the best green roof provider in their area.

The first question to ask the green roofing installer is what type of roofing membrane they specify for green roof applications.

Most membranes, including those used for green roofs, are designed to be exposed and to shed water.

A conventional roofing membrane applied to a green roof will most likely result in premature roof failure.

Another key question in green roof design pertains to roof load.

Many green roofs can weigh up to 35 pounds per square foot.

The extra weight can exceed the amount that the roof deck is able to support, causing unforeseen problems.

A properly designed green roof system should only weigh up to 18 pounds per square foot — with saturated vegetation.

A final issue to discuss with an installer is the type of insulation specified in the green roof design.

As mentioned before, the traditional ISO insulation quickly loses its ability to retain heat.

Make sure the installer uses XPS insulation, which has a guaranteed R value and will help reduce energy use for decades.

In general, the best place to start a search for a reputable green roof installer is with your local U.S. Green Building Council chapter.

They can provide a list of area contractors that specialize in green design. The directory is also available online at

Also, and provide an extensive, state-by-state list of corporate, sales, and property tax breaks, rebate programs, grant and loan programs, and other financial incentives for green building and sustainable energy initiatives.

John Francis is the second-generation owner and CEO of NV Roofing. His company has provided residential and commercial roofing solutions in the Washington, DC, metro area since 1963. John is a leader in the local green roofing movement. NV Roofing installs field-proven vegetative and non-vegetative green roofing systems, which utilize recycled materials and last more than 40 years. For more information about NV Roofing visit
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