High-Wind Asphalt Roofing — JLC Online

For a long-lasting roof on the coast, be meticulous, use wind-rated shingles, and keep plenty of peel-and-stick tape on hand

(Photo by Vince Lupo)

Veteran roofers often urge their apprentices to "think like a raindrop" when installing roof membranes and flashings. In most places, this means understanding that water obeys the law of gravity. But in a coastal environment, that raindrop is likely to behave like a speeding bullet when it’s carried on a gusting wind. The very best of roofs have little defense from a direct assault by a hurricane, and wind-driven rain isn’t the only hazard. On sunny days, intense ultra-violet light wreaks havoc on roof coverings. For many coastal roofers, protection against these elements lies in a two-pronged strategy: Install the most durable roofing materials possible, but back them up with secondary barriers to help prevent water from pouring into the house if the big one strikes.

FIRST LINE OF DEFENSE

No roof covering will offer much protection if the underlying sheathing is blown off. In high-wind zones, the sheathing material should be plywood or a premium grade of OSB, such as AdvanTech (Huber Engineered Woods; www.huberwood.com ). Half-inch panels are acceptable for 16-inch o.c. rafters, but 5/8-inch panels should be used to span 24-inch o.c. trusses.

The edges of a roof — eaves, rakes, and ridges — are the most susceptible to wind damage. It is vital that these locations be tied securely to the framing.

Run full sheets along the eaves and along the ridge, stagger the seams, and don’t use anything smaller than a half-sheet (4×4 feet) along rake edges.

Fasten sheathing with full-head, ring-shank, or screw-shank 8d nails, or 2-inch-long, #8 screws driven with an auto-feed screw gun.

Follow a tight nailing pattern: 4 inches o.c. along edges, 6 inches o.c. in the field.

For additional peace of mind: Install blocking along the edges of all perimeter sheets and nail securely.

After he’s finished nailing the sheathing, builder Mike Guertin of East Greenwich, R.I. (author of Roofing with Asphalt Shingles. Taunton Press, 2002), always crawls into the attic to verify that all the nails have hit their mark. Any misses he discovers are driven back out and re-nailed into framing. "If you miss one nail, you’ve probably missed the whole row," Guertin says.

SEALING THE SHEATHING

If high-quality sheathing is securely fastened, it may survive a direct hit from Bertha even if the shingles don’t, but the driven rain will flow into the house through the joints between panels. The most efficient protection is to cover every seam with a narrow strip of self-adhering underlayment or a 4-inch strip of peel-and-stick flashing tape (Figure 1).

FIGURE 1. In the event a wind storm rips the roof covering off a house, peel-and-stick flashing tape applied to sheathing joints provides a secondary moisture barrier. (Photo courtesy Institute for Business & Home Safety, Fortified Builder’s Guide)

Like many roofers, builder Guertin covers vertical sidewall intersections (Figure 2) and valleys with wider strips of Ice & Water-shield. In addition to storm protection, self-adhering flashing membranes serve as a backstop to catch wind-driven rain that might get past the flashing. Guertin’s practice of taping all possible entry points for moisture has an added advantage: "Once the peel-and-stick is in place," he says, "the roof is dried in."

FIGURE 2. SIDEWALL FLASHING

Sidewalls should be protected with liberal amounts of a peel-and-stick roofing membrane, applied in the numbered order shown. In addition, oversized step flashing will help block wind-driven rain, and a "kicker" at the lowest step flashing will divert water from soaking the sidewall as it drains. (Illustration by Rick Vitullo)

Over a sealed sheathing, every coastal roofer I talked to still relies on 30-pound felt secured with galvanized roofing nails as the underlayment of choice. Recently, however, a number of housewrap manufacturers have introduced "roof wraps," but it’s still too soon to say how useful these products are going to be (see "Housewraps for the Roof," below).


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