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This house was exposed to a direct hit from the eyewall winds of Hurricane
Ivan in 2004. It had been re-roofed with wind-rated shingles including re-nailing
the deck about 4 years before Hurricane Ivan struck. If the porch roof had not come
off, which in turn knocked off the chimney, there would have been very little damage
to the roof. No shingles came loose other than those next to the damaged chimney.
In addition, there was limited failure of the anchorage of the ridge vent.
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By contrast, this house was next to the house shown above and lost most of its shingles and some of the sheathing at the gable end.
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As noted in What To Do When Re-Roofing
building codes generally allow homeowners to install a second layer of asphalt
shingles over an existing layer of old shingles. However, for a more secure roof
during hurricanes and other high winds areas, it is strongly recommended that
you remove the old shingles before installing the new ones. Besides giving you
more confidence that the shingles will seal properly (wind rated shingles have
only been tested as applied over a flat roof deck; not over the bumpy surface
of an existing layer of shingles) and that you will have a more wind resistant
roof covering, it gives you the opportunity to take several additional steps
(replacing damaged or decayed sheathing, re-nailing your roof sheathing to
increase its resistance to being lifted off in a hurricane, and applying a
high quality underlayment to make your house safer; all at relatively little
extra cost.
If you followed the directions for installing a high quality underlayment, all roof
edges should have a metal drip edge installed and the drip edge at the eaves should
have adhesive sealant under the edge to keep water from seeping under the drip edge.
Complete the seal at the edges by applying a 4-inch wide layer of asphalt adhesive
along the roof edges (eaves and rakes) to seal the edge and to adhere the perimeter
shingles or starter strip (at the eaves) to the edge of the roof. Similarly, the
Florida Building Code requires that shingles overlap the horizontal flange of all
flashing and be set in approved flashing cement. This means that the horizontal
portion of flashing at wall intersections or around any protrusions through the roof
have to be coated with an approved flashing cement that will glue the shingles to
the flashing.
Choose shingles that match or exceed the wind rating for the design wind speeds in
your area. There have been some dramatic improvements in the wind ratings of shingles
in recent years. It wasn't too long ago that the highest rated product was only rated
for about 65 mph. Now, products are being evaluated with a new test method and rated
with letters such as D, F, G, and H. The H rated shingles are rated for 150 mph while
the G is rated for 120 mph, F for 110 mph and D for 90 mph.
These ratings are established at the time of manufacture based on the resistance of
the sealed tab to uplift. The adhesive strip is critical to this rating. The uplift
resistance has been correlated with the forces expected on that shingle for the
indicated wind speed based on wind load research. It is best seen as a relative
rating of the shingle products based on their ability to resist tab uplift at the
time of manufacture, not a guarantee that it will not blow off in a storm with those
winds after it has been installed on your roof for a number of years. Nevertheless,
the ratings do indicate that the tabs of higher rated shingles are more likely to be
well adhered to the top of shingles below. The Florida building code requires that
shingles be rated for the design wind speed where the home is located up to 110 mph
(F-rated). F-rated shingles or those tested using the older Miami-Dade County test
protocol that requires testing of shingles by subjecting them to 110 mph winds for
one hour are required anywhere the design wind speed is 110 or greater. Since the
new higher rated shingles now exist, we recommend that you use one that matches or
exceeds the design wind speed for your home's location. The Asphalt Roofing
Manufacturers Association (ARMA) has prepared a document describing the new rating
system (ARMA Discussion of new high wind standards for shingles).
To maximize the high wind resistance of shingles it is recommended that shingles be
attached with nails (not staples) and that the nails be installed by
hand instead of by a pneumatic nail gun. If a pneumatic nail gun is used, the
settings need to be checked frequently to ensure that the nail heads are not being
driven incorrectly. Both ARMA and FEMA have prepared documents that illustrate
proper nailing of shingles
(ARMA Nail Application of Asphalt Shingles and
FEMA Asphalt Shingle Roofing for High Winds).
The general recommendations for the nails are that they have a minimum head diameter
of 3/8-inch and that they penetrate 3/4-inch into a wood deck or completely through
plywood or OSB sheathing. In areas with design wind speeds greater than or equal to
120 mph, the recommended fasteners (required in the High Velocity Hurricane Zone) are
ring shank nails with a minimum of 20 rings per inch and the penetration of the
fasteners is 1-inch into the wood deck and clear through plywood or OSB sheathing.
The nails are required to be corrosion resistant. Galvanized steel, stainless steel,
aluminum or copper roofing nails are allowed in the Florida Building Code. The FEMA
technical guidance recommends the use of stainless steel nails for homes within 3000
feet of salt water. The location of the nails on the shingle is critical and the
manufacturer's recommendations need to be carefully followed. The nails should not
be installed in the adhesive strips. Some manufacturers have added lines to show
installers where to apply the nails for their particular product.
There is a debate concerning whether 4 or 6 nails should be required for three tab
shingles. While many shingle products will pass the certification tests with only
4 nails the issue is whether the extra nails will provide an additional measure of
protection from losing shingles once the tabs lift. Thus, the 6-nails per shingle
requirement that is generally recommended for high wind regions is considered prudent
for improving long term performance as the shingles age. We recommend that 6-nails
be used to attach each three tab shingle in high wind areas. If you are using
dimensional shingles, follow the manufacturer's recommendations for high wind
installations.
Make sure that the shingles do not extend more than 1/4" beyond the edge of the roof
if you have a square drip edge. If you have a FHA type of drip edge, we recommend
that the shingles be cut flush with the drip edge.
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FHA-type drip edge with shingles
cut flush with the drip edge. This
helps prevent wind from getting up
under the edge of the shingle when
it sticks out past the fascia
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Profile of FHA-type drip edge
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The ARMA website, www.asphaltroofing.org
provides access to a number of documents and technical bulletins, most of which can
be downloaded for free. Other publications are available for purchase by visiting
the ARMA publications
page.
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You can check specific product approval information for a particular shingle
at the
