by Tom O'Brien
(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 (4x4 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
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
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
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).
Regardless of the material, overlaps should be 6 inches all the
way around and nail spacing should be 6 inches along the edges and
12 inches in the field. Capped head nails are better than standard
roofing nails or staples, especially if the felt will be exposed
for more than a day or two.
For roofing applications in areas where the "Basic Wind Speed" is
110 mph or greater — which amounts to almost any place that's
within 50 miles of the shoreline — the 2000 IRC requires
nothing more than six fasteners per shingle and corrosion-resistant
fasteners for the underlayment (Figure 3).
FIGURE 3. HIGH-WIND SHINGLE NAILING
The 2000 IRC requires a six-nail pattern for asphalt shingles.
The more stringent 2003 IRC has eliminated this requirement in
favor of wind-rated shingles with stronger adhesive sealing strips.
Whatever shingle is used, be sure to read the wrapper for specific
nailing recommendations, as they do vary by make and model.
(Illustration by Rick Vitullo)
Things get a bit tougher in the 2003 IRC. This latest version of
the code drops the six fasteners requirement in favor of shingles
that are tested and approved under the ASTM D3161 standard
(modified to 110 mph) for use in wind zones of 110 mph or greater.
Many roofing manufacturers now offer a line of these "high-wind"
shingles (see "For More Information"), and they
tend to cost about $15 to $20 dollars more per square than a
comparable standard variety. According to R. Allan Snyder, Manager
of Product Compliance for CertainTeed Corporation, what sets this
type of shingle apart is not its weight or thickness, but the
quality of the sealant that sticks the overlapping tabs together.
"Even the lightest of shingles can pass the 110-mph test if the
sealant is formulated correctly," says Snyder. However, he points
out there is a big difference between surviving a big gust and
surviving years of wind and sun. For the best performance in
coastal environments over time, Snyder urges builders to choose a
premium laminated shingle from their supplier's high-wind line.
"Heavier and stiffer is better," he says.
Nail placement is critical to maximize the chemical adhesion
between overlapping shingles as well as to prevent leaks.
Manufacturers have very strict stipulations for nail placement and
those requirements can vary between makes and models of shingles.
Even veteran roofers should make a habit of reading the
manufacturer's instructions, especially if they're using an
To maximize the mechanical adhesion, shingles should be nailed, not
stapled. The nail head must be driven perpendicular to the surface
of the shingle and the nail head must be flush. Hand-nailing is the
most accurate way to ensure that shingles are fastened properly.
Roofers who prefer pneumatic fastening systems should choose nail
guns that have a depth-of-drive adjustment — instead of
adjusting the air output from the compressor. Also, since a shingle
offers less resistance to penetration as it warms up, it's
important to monitor the depth of drive on air guns throughout the
As with sheathing, the shingles that lie along the edges of the
roof take the most abuse from the wind. If one or two start to peel
up and offer the wind some leverage, the entire roof could open up
like a zipper. Professional roofers have different strategies for
adding fastening strength to these vulnerable areas:
John Criner, a roofing contractor in Kitty Hawk, N.C., applies a
line of starter strip up the rake edges, as well as along the
Instead of starter strip, Jimmy Waller of Goff-Waller Roofing in
Lakeland, Fla., runs a bead of roofing cement under the outside
edges of the rake shingles.
Joe Filippone, a roofer who has spent his entire career on
wind-swept Block Island, R.I., firmly believes in "sticking" each
and every shingle. Filippone's technique is to apply a
quarter-sized dollop of Geocel Roof Patch (www.geocelusa.com)
beneath both corners of each tab. On a typical (20 square) roof,
he'll go through six to eight cases of Geocel. "Yes, it's a
hassle," he admits, "but it's a lot easier to 'stick' it than to go
back and fix a big chunk that's blown off."
ROOF FLASHING TIPS
Although they can be tedious to assemble because both sides must be
shingled at the same time, woven valleys are worth the trouble in
high-wind zones (Figure 4). The interlocking weave not only
shields the valley with a double layer of shingles, but the
alternating tabs work like step-flashing to ensure that wind-driven
rain has nowhere to go but out.
FIGURE 4. WOVEN VALLEY
Woven valleys work best in high-wind regions. The interlocking
tabs shield the valley with a double layer of shingles and prevent
water from working its way into the roof. (Illustration by Rick
A woven valley can be difficult to create where roofs of radically
different pitches meet. In those instances, a closed-cut valley is
the best second choice. An open valley should be avoided because
it's the least wind-resistant of all.
Roofer John Criner believes that pre-manufactured step flashing
cards are too small to offer adequate protection from coastal
wind-driven rain, so he bends his own. Criner's 8x 8-inch steps
allow for overlaps on all sides that are at least an inch longer
than what he could get from pre-made flashing. Copper, lead-coated
copper, and stainless steel are more durable flashing materials
than aluminum or galvanized steel.
Today's asphalt shingles rely on sealant as much as on nails
— or more than they do on nails — to resist high winds,
but the sealant won't activate in cold temperatures. On winter
days, don't apply roofing if the air temperature is below freezing.
Work on the sunny side of the roof as much as possible and check
the first shingle to verify that its sealant is sticking. If the
sealant isn't activating, you must hand-tab each shingle with
plastic roof cement. Also, if the shingles are applied to a beach
house on a windy day, sand may stick to the sealant, also
preventing a good bond. The only solution in this case is to wait
for a calmer day.
Tom O'Brien is a carpenter and writer in New Milford,