By Wayne A. Endicott
Sooner or later, a roof reaches the end of its useful life and must be replaced. Often remodeling projects include a new roof. But how do you make sure that the roof you install is going to function the way it is supposed to—keeping the inside of the home dry and free of trouble caused by moisture leaking into the home? And how do you ensure that it will last for the longest possible time?
There's a lot to ensuring good roof performance. Chuck Scisco, senior technical director of the National Roofing Contractors Association, Rosemont, Ill., says that choosing the right shingle for the projected job is the first step. Often, the choice will be determined by the style of the house. Asphalt, fiber glass, cedar shake and other materials all can give a satisfactory final result — if certain steps are followed to ensure that the roof isn't a problem waiting to happen:
Tear-off or not?
Although some code jurisdictions permit the installation of a new roof over an existing roof, the practice is a bad idea, Chuck cautions. "The existing roof may be hiding an existing problem," he explains. "Although it may be costlier and require more work, we recommend a total tear-off each time a roof is replaced."
With the old roof gone, the contractor can perform a complete inspection of what problems it might have been hiding. After all, the underlayment is as important as the shingles in keeping water from penetrating the roof. Completely exposing what lies beneath affords the opportunity to find and remedy common problems such as rot, mold or mildew growth, missing or damaged underlayment, as well as problems with insulation.
Be sure to inspect the metal flashing, too, since it is a critical piece of managing water intrusion. "We suggest that it is always a good idea to replace old flashing material," Chuck says.
If you find that you have to replace the underlayment on a low slope roof (a 3-inch rise or less in 12 inches of roof), install a double layer of underlayment, using 36-inch wide material and overlapping it every 19 inches. For a steeper slope, a single layer is usually sufficient, with 36-inch width material overlapped 6 inches and the seams offset to prevent water penetration between sheets of underlayment.
Another recommendation for climates where the January temperatures average 25 degrees Fahrenheit or less, is to install an ice protection system, which should extend at least 36 inches back from the inside face of the outside wall. These systems prevent ice damming, which that can cause water to back up under the shingles as snow and ice melt, damaging the materials below.
Finally, venting is a must for any sound roof. An improperly vented roof is an invitation to disaster, since condensation can occur on cold surfaces such as roof sheathing. Venting allows air flow to remove this potentially damaging moisture. Says Chuck, "For every 150 to 300 feet of roof deck, we recommend at least one foot of vent, either at or near the ridge and at the eaves or soffit."
For a house that has that has both soffit vents and ridge vents, the International Building Code, specifies one square foot of ventilation for every 300 hundred square feet of attic space. If there are no ridge vents, that number drops to one square foot for 150 square feet.
For more information on recommended practices, Chuck says, contractors can go to the NRCA Web site at www.nrca.net and follow the prompts to view the association's roofing manual online.
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