Roofing Roofs Reflective

Reflective, Roof, Reflectivity, Emissivity, Roofing, Green Building, Green Builders, Energy-Efficient Homes, Green HousesPlease Note:This website explains green building for a climate zone comparable to North Texas or Central Texas, such as the climate of Waco or Dallas-Fort Worth, Texas. It is important to hire a green builder who is an expert in energy-efficient building in your climate zone.

Reflective Roofs in Green Building

Roofing Materials for Green Homes 

This website is for the climate zone that includes North Central Texas or the DFW area such as Plano, Keller, or Dallas-Fort Worth Texas.  Regardless of your climate zone, the first priority for green building or energy-efficient remodeling is to hire an energy consultant and a green builder who understand and use up-to-date green building practices for your area. 

Cool roof performance is a function of two radiative properties: Solar reflectance and infrared emittance. These two properties define the “coolness” a roofing product contributes to green building.

Solar reflectance is a decimal number less than one that represents the fraction of light reflected off the roof.  If a high reflectance material has a value of  0.70 (70%), only 30 percent of the light from the sun is retained by the roof.   

Solar reflectance is the most important characteristic of a roof product in terms of yielding the highest energy savings during warmer months. The higher the solar reflective value, the more efficient the product is in reflecting sunlight and heat away from the building. This reduces the temperature of the roof.

Think of the effects of dark versus light clothing on a sunny day. Because dark colors reflect less solar energy, dark is hot and light is cool. The same principles apply to roof temperatures. Light-colored roof materials make for a cool roof by reflecting more of the sun’s rays.

Reflective roof coatings act like mirrors, reflecting the sun’s radiant energy back into space. These reflective roof coatings, also known as albedo (a fancy word for reflectivity) coatings, are products applied to roofs to reduce solar heat.

Infrared emittance is a decimal number less than one that represents the fraction of heat that is re-radiated from a material to it’s surroundings.  The emittance of a material refers to its ability to release absorbed heat.  One example is a metal tool left in the sun. It is hot to the touch because it has a low emissivity value.

Emissivity can also contribute to a cool roof in warm, sunny climates like Dallas-Fort Worth. Roofing products with high emissivity can help reduce the cooling load on the building by releasing the remaining heat absorbed from the sun.

For buildings dominated by cooling loads, it makes sense to provide roofing products with high reflectivity and high emissivity. These products help reduce cooling loads because the roof is exposed to the sun for the entire operating day. 

Caveat: Because roof coatings tend to lose their reflectance properties over time due to dust and dew, regular cleanings and even reapplications are needed.

Do you need an energy consult
or energy audit or
green builder/remodeler
in North Central Texas
or the Dallas-Fort Worth area?
Contact Terry Jensen
Frugal Energy, LLC
817 443-2553 or 972 251-1532

 

Contact
Copyright © 2007-2011 Dallas-Fort Worth Green Building and Renewable Energy. All rights reserved.Reprinted with permission which is not universally given. Please contact DFWGreen Building and Renewable Energy for permission in writing before using thesecopyrighted materials.

Note: The opinions expressedherein are exclusively those of the writers or other participants and do not necessarily reflect theposition of CyberParent,LLC. They are not intended to take the place of advice of ahealth, legal, or other professional whose expertise you might need to seek.This website explains green building and green remodeling for a climate zonecomparable to North Central Texas or Dallas-Fort Worth, Texas,  It isimportant to hire a green builder and an energy consultant who are experts inenergy-efficient building in your climate zone and who use the most up-to-dategreen building information.