Green Building Roofing Best Practices
Make sure your roofing contractor replaces damaged sheathing, underlayment, and flashing. These materials will protect your home even more than the shingles. Also, be on the lookout for mold on the roof sheathing.
The type of roofing you choose can have a serious impact on your health and on the environment. Slope roofing materials, such as asphalt-based rolled roofing and shingles, will offgas toxins when heated by the sun. Flat roofing materials, such as tar and gravel, will continually offgas when heated by the sun, emitting known carcinogens such as VOCs from asphalt, including benzene, polynuclear aromatics, toluene and xylene. Although roofing materials are located outside the living space, odors can enter the home through doors, windows and vents.
78% of total annual roofing dollars spent in the US is spent on re-roofing. Re-roofing is not only expensive, but it sends used roofing materials to landfills, where the polluting contents continue to offgas and leach into the soil and groundwater.
Unfortunately, re-roofing your house is often a necessity. But a new roof with good air sealing, insulation, and ventilation will save energy and make your house more comfortable. Many unhealthy and persistent mold and mildew infestations began with an undetected roof leak. No type of roofing installation is foolproof, but the use of high quality roofing materials and skilled installers will reduce the risk of leakage.
Here are some tips to help guide your roofing decisions:
Consider the System as a Whole
In new construction, choice of roofing materials should be integral with other decisions about the building. The roof is your main defense against water leakage in your house. Early in the decision-making process, figure out your roofing and how it will integrate with the rest of the house.
Calculate How Much Roofing You'll Need
Roofs are measured in 100-square-foot areas, or "squares". Three bundles of three-tab shingles typically equal one square: laminates come in four bundles per square. It's a good idea to calculate beforehand how much roofing material you'll need so that you'll have an easier time comparing bid from contractors.
- multiply the overall length and width of each roof section to determine its area
- Add 10% to allow for waste, then divide by 100 to determine how many squares you'll need
If the roof is new or you're having the old shingles removed, you'll need an underlayment (roofing felt) to create a moisture barrier for the wood sheathing and rafters underneath. You may also have to install an "ice-and-water shield" along with the eaves and valleys where two wings of the roof intersect. New drip edges and metal flashing are often needed around pipes, chimneys, and the like.
Adhesives used in roofing applications can emit harmful VOCs. They are especially toxic during application and curing (drying) periods. Water-based adhesives are better because they only release water vapor as they dry, but they are not necessarily 100% safe. Use mechanical fastening, a range of processes that utilizes a variety of fasteners including nails, nuts and bolts, screws, and rivets to assemble materials without heating or adhesives.
Provide a Light-colored or Reflective Roof
Dark roofing materials absorb heat and make the house warmer in the summer, whereas light-colored roofing reflects heat away from the building. Consider the following:
Reflective roofs help reduce the "heat island effect", a phenomena in which heat-absorbing buildings can increase the outside air temperature in urban areas by two to eight degrees Fahrenheit. Unless the building has a highly insulated roof, it is generally advisable to provide a reflective roof surface.
Light-colored roofing also reduces heat buildup through the roof. It may also last longer because it does not thermally expand and contract as much as darker colors.
Install Radiant Barriers
Reflect heat away from your home by installing a radiant barrier on the underside of your roof. A radiant barrier is simply a sheet of aluminum foil with paper backing, or metalized mylar sheet material. When installed correctly, a radiant barrier can reduce heat gains through your ceiling by about 95%.
You can install radiant barriers by stapling them to the attic rafters - do not staple them to attic floor joists where dust collects on them more quickly. Use laminated foil-backed OSB for new roof construction, reflective side down.