Roof! Your Home’s Top Dog

History

Did you know that the concept of roofs came about as primitive populations needed a way to be protected from the rain?  But that’s only half the story.  These early populations saw protection from the rain as a more pressing concern than protection from other outside elements such as sunlight.  Across different parts of the world, people constructed the roofs of their buildings with the ultimate goal of protecting themselves from the rain.  For example, flat roofs were associated with dry climates where the drainage of the water from frequent rainfall was not much of a concern but protection from a rare but heavy rainstorm was an issue.  Sloped roofs were associated with climates where there was frequent rainfall and the drainage problem was a huge concern.  Historically, the primary goal of a roof was to keep water from leaking into the building.  But beginning in the 19^th century, people started viewing roofs as structures built to defend against both rainfall and sunlight.

Roofs: Style, Covering, and Material

Style

• Flat roofs
• Pitched or sloped roofs

Covering

There are two types of roof covering that set out to resist the penetration of water or other leaks: 1) separate shingles; 2) continuous layer.

• Separate shingles are usually composed of flat pieces of a waterproof material that are joined tightly together and placed at the uppermost part of a building so that water or similar leaks can’t break through the joints.
• A continuous layer is a full membrane of a sheet material that is resistant to water or similar leaks.

Material

There are different kinds of roofing materials that are made for different kinds of buildings and each material has its own method of construction.  To determine the appropriate roofing materials for a particular building, one must first identify the purpose of the building.  The purpose of a building is usually identifiable from the traditions, regulations, and climate of a given locale.  Once the purpose of a building has been identified, the right kind of roofing material can be constructed for it.  The material of a roof can range from aluminum sheeting, glass, and concrete to wheaten straw, sea-grass, and banana leaves.

Roof Performance Criteria

Many people appreciate having a roof over their heads.  And just as some heads are bigger than others, some roofs are better than others.  Roof performance, especially for residential purposes, is rarely evaluated based on the ability to prevent water leaks; instead, roof performance is now measured by roof surface temperature.  Roof surface temperature can be thought of in terms of solar reflectance.  The surface temperature of the roof is determined by how much of the sun’s rays the roof is able to reflect away from the building.  In effect, Roof A performs better than Roof B if Roof A can reflect away a greater amount of the sun’s rays.  Roof A is better in the sense that it is more energy efficient than Roof B in cooling the air inside the building.  A homeowner can reduce the need for air conditioning with the right type of reflective roofing.

Tips on Purchasing

Energy efficient roofs, specifically ENERGY STAR rated roofs, can help to reduce a homeowner’s energy bills.  According to a conference report by the Sustainable Energy Fund, Americans spend about $40 billion annually in order to air condition buildings; this amount represents a sixth of all the electricity usage generated here in the United States.  Roofs are the uppermost defense against energy inefficiency and there are some guidelines that homeowners can follow to structure their uppermost defense properly:

1. Know what roof style, covering, and material you need.
   1. Slope or flat?  Aluminum or glass?
2. Find out the solar reflectance to maximize you the energy efficiency of your roof.
   1. It is recommended that low slope roofs have an initial solar reflectance of greater than or equal to 0.65.  After three years, the solar reflectance must be greater than or equal to 0.5
   2. It is recommended that steep slope roofs have an initial solar reflectance of greater than or equal to 0.25.  After three years, the solar reflectance must be greater than or equal to 0.15
3. Work with your local Mean Green List contractor to address your questions.