Reflective roofs return multiple dividends

Building Operating Management, May 2000 by Sturdevant, Nicole

The snowball effect: reduced cooling loads, lower energy bills and improved IAQ

Many building owners are starting to realize the benefits of energy upgrades. Few, however, appreciate the potentially sizeable payback of reflective roofs. This applied roofing technology minimizes building heat gain and attacks energy waste in a critical area: interior cooling loads. It also is one of a number of effective strategies against the phenomenon of "urban heat II islands" - a temperature increase in concentrated areas caused by radiant heat from dark surfaces, such as roofs and asphalt parking lots. This less-than-desirable condition indirectly impacts air quality and energy costs.

"Building owners will consider wrapping pipes, putting reflective glazes on their windows, upgrading their lighting fixtures and even adding roof insulation - but most owners rarely look at the roof itself," says Sam Everett, director of corporate communications at Stevens Roofing.

Fortunately, owners are starting to look at reflective roofs as a way of reducing their energy costs.

The U.S. Environmental Protection Agency's ENERGY STAR(R) roofing program promotes reflective roofs, which are energy-efficient and environmentally friendly. The organization is also helping to educate building owners about the benefits of reflective roofs.

Owners have a few choices when it comes to reflective roofs: apply a reflective coating, install a reflective membrane or install a metal roof made of galvanized or other coated metal. Each option has its own benefits.

Coatings remain effective from five to 10 years, depending on how well they are maintained. Reflective membranes can last from 10 to more than 20 years when properly maintained. Metal roofs have a broad longevity range of 20 to 50 years. Their life span depends on the type of metal used to make the roof product, its thickness, whether or not it's coated and other variables that apply to all roof products, such as amount of weather exposure, foot traffic and maintenance.

A reflective roof can be installed or applied over almost any type of roof material.

No matter what method building owners use to make their roofs reflective, comparable overall benefits can be realized.

OPERATING COST SAVINGS

The concept is simple. Reducing the temperature of the roof reduces the building's interior temperature and reduces the running time of the air conditioning system. Also, lowering the temperature at or above the roof's surface means the air conditioning unit doesn't have to work as hard to cool down the make-up air. Cutting back on air conditioning use lowers a building's energy costs.

While most large buildings benefit financially from a reflective roof, those in the warmer states will see the most significant energy savings.

For whole building renovation projects, another benefit of reducing cooling loads is being able to install smaller, more efficient air conditioning units.

Equipment runs more efficiently at full load, and downsized equipment runs at full load more often. Downsized equipment is also less expensive.

Heating costs can also be offset during winter months when a reflective roof is used with adequate insulation.

The correlation between insulation and reflective roofs has been examined for a while. Recently, ASHRAE Standard 90.1-1989 was revised to include information about reflective roofs. The new standard - 90.1-1999 - takes into account new developments in roofing technology and design.

Hashem Akbari, a researcher at the Lawrence Berkeley National Laboratory, worked with the committee to have reflective roofs included in the standard.

"Those buildings that have highly reflective roofs can actually reduce their levels of insulation," he says.

Even with an increase in heating costs, buildings in cooler climates can save on overall energy costs, Pat Downey of Merik Inc. explains: "Savings are based, in part, on fuel type. Since cooling units are generally electrical and heating units are generally gas, owners can save on electricity even if their heating costs increase slightly."

As electricity rates continue to increase and gas rates continue to decrease, these cooling cost savings should continue to rise.

Reflective roofs also reduce thermal shock, which occurs when cool rain hits a hot roof, causing a sharp drop in temperature.

During these temperature changes, a roof expands and contracts, causing unnecessary stress on the roof. This condition also degrades the seams, making them more susceptible to leakage, according to Jamie Moore, marketing specialist at Conklin. Reflective roofs maintain a more constant temperature, so thermal shock and associated problems are significantly reduced.

Cooling a roof may also prolong the life of roofing components, according to Jim Leonard, president of Elastomeric Roofing Systems.

"Everything on a roof ages at a faster rate when heated up," he says.

Others also speculate that reflective roofs slow down the rate of chemical reaction by keeping components cool, extending the lives of roofing materials.