When most people hear the words "metal roofing," they think of
ridged or corrugated ag panels, or perhaps standing-seam
roofing. Metal shingles are less familiar, but they're my
favorite roofing material. I've installed dozens of
metal-shingled roofs over the past ten years or so.
When I bid a metal-shingle roofing job, I charge two to two and
a half times what I would to do the same job with a good grade
of asphalt shingles. But because a metal-shingled roof should
last at least 50 years, it's cheaper than asphalt in the long
run. Customers appreciate the added value, and they like the
distinctive textured look. And from my point of view, the light
weight of metal shingles — about 40 pounds per square for
the aluminum shingles I use, compared to 150 pounds or more for
asphalt — does away with a lot of heavy lifting.
But working with metal shingles requires a different attitude
than working with conventional shingles. The relatively short
life expectancy of an asphalt roof helps limit the effects of
installer error. Many mistakes that represent potential leak
points don't develop into actual leaks before the roof is
A metal-shingle roof, on the other hand, should outlive the
roofer. So it's essential to get all the details right,
especially around roof penetrations and in other tricky areas.
Most metal-shingle manufacturers offer hands-on training in how
to install their products correctly, and that's by far the best
way to get started on the right foot (see "Installer Training,"
Most metal-shingle manufacturers offer some sort
of installer training, but the only program I have
firsthand experience with is the one offered by
Classic Products at its facility in Piqua, Ohio. It
consists of two days of hands-on training on a
full-sized test deck inside the factory. The deck
includes just about every feature and roof
penetration an installer would be likely to
encounter in the field.|
Different sessions are offered for each of the
company's roofing products, and they rotate so that
each session is offered several times a year.
There's no charge for the training itself, but
participants are responsible for their food,
lodging, and travel expenses.
If you can't take time to go to the factory, the
company will send a trainer to your job site. I
arranged for that once when setting up a new crew,
and it worked out well. There is a charge for that
service, but it's at least partly offset by the
fact that the trainer actually works on the site,
adding another pair of hands to move the job
Aluminum or Steel?
Metal shingles are available in both aluminum and steel. I
prefer aluminum because it won't rust if the paint is
scratched. It also weighs less than steel, making it easier to
Reflective finishes. I use
aluminum shingles from Classic Products (800/543-8938,
which come in a variety of "spectrally reflective" Kynar paint
finishes. These absorb colors in the visible light range, but
reflect infrared and ultraviolet rays to reduce thermal gain
and cut cooling costs, even when dark-colored shingles are used
(see "Cool Roofs for
Hot Climates," 6/03). The reflective finishes used to be an
extra-charge option, but Classic recently made them standard
across its product line.
Smooth or granular? In
addition to the smooth base coat, all of the company's steel
shingles receive a textured powder-coat finish to resist
scratches and prevent rust. Aluminum shingles are available
either with or without the textured topcoat. The smooth
shingles are subject to minor scratches from foot traffic, but
these are inconsequential because they're invisible from the
ground and the aluminum substrate won't rust. My customers
split about evenly between those who like the shiny paint and
those who prefer the textured powder coat. The textured finish
is made up of several colors, giving it a blended look that's
something like an asphalt shingle.
Preparing the Deck
The light weight of aluminum shingles makes them ideal for
reroofing applications. By using 2 1/2-inch nails, we've
successfully applied metal shingles over three layers of
existing asphalt shingles. Building inspectors will usually
okay this as long as there's no visible sag in the roof
framing. According to Classic Products, most worn-out asphalt
roofs will already have lost more than 40 pounds of ceramic
granules per square, so the added weight of the aluminum
shingles shouldn't pose a problem.
Underlayment. Whether you're
roofing over an existing asphalt roof or a new deck, the first
step is to apply an approved underlayment. We used to use
30-pound felt, but now we use a multi-layer synthetic material
called RoofTopGuard II (see Figure 1), which is made in Finland
and marketed in North America by Nemco Industries
Figure 1.A proprietary underlayment is fastened to
the deck with plastic-cap underlayment nails. Standard 30-pound
felt also works, but the synthetic laminate is tougher, more
durable, and easier to apply.
It's very tough, more slip resistant than felt, and it can
serve as a temporary roof for six months or more. What I really
like about it, though, is its light weight: A 60-inch-wide roll
contains ten squares of material and weighs just 40
Shingling the Field
Fastening methods vary from manufacturer to manufacturer, as
well as among different product lines from the same
Starter strips and nailing
clips. In the case of Classic's rustic shingles, for
example, the hooked butt of the first course of shingles
engages a slot in a combination of starter strip and drip-edge
at the eaves (Figure 2).
Figure 2.The first course of shingles is hooked
against a combination of starter strip and drip-edge nailed to
The shingle is pulled upward into position and secured with
two threaded aluminum nails. Neither penetrates the roofing
itself: One passes through a prepunched hole at the top
right-hand corner, and the second is driven through a
prepunched hole in a metal nailing clip that engages a flange
at the shingle's upper edge (Figure 3).
Figure 3.The butt of each shingle above the eaves
is hooked over the top flange of the shingle below; a similar
side flange engages the previous shingle in the same course.
Shingles are ordinarily laid from the lower left of the roof to
the upper right.
Classic's lower-profile Oxford shingles are hooked to the
starter strip in about the same way but have no integral
nailing tab at the top edge. They're secured to the deck with
five nailing clips per shingle.
With both styles, additional locking flanges secure the edges
of the shingles where they meet. Above the eaves starter strip,
the butt of each shingle engages the upper edge of the course
below. There are no exposed fasteners, and thanks to the
mechanically interlocking shingle edges, the resulting roof is
capable of withstanding 110-mph winds.
Foam inserts. Steel shingles
are pretty crush resistant, but you can damage the aluminum
ones by walking on them carelessly. The manufacturer recommends
working from above, where possible, to avoid deforming the
The alternative is to install a manufacturer-supplied
polystyrene insert under each shingle before it's fastened down
(Figure 4). The inserts increase the cost of the job by about
4% to 7%, depending on the style of shingle, but it's well
worth the added cost. Besides protecting the shingles during
installation, the inserts prevent them from being damaged by
the chimney sweep or satellite TV guy who comes along after
Figure 4.Aluminum shingles can be damaged by foot
traffic. Polystyrene inserts add stiffness and help protect the
roof both during and after installation.
Factory training really pays off when it comes to flashing.
There are manufactured solutions to many common conditions, but
others are best handled with site-bent flashing made from
matching coil stock (Figure 5). For the occasional roof that
calls for something totally unexpected, a factory expert can
help you figure out what's needed and even fabricate the
solution for you if necessary.
Figure 5.Site-bent coil stock comes in handy in
many problem areas. At this roof jog, a continuous strip of
coil stock fills the gap between the starter strip and the
first full course of shingles. While it would have been
possible to cut and bend individual shingles to accomplish the
same thing, the faster coil-stock method was chosen because the
area wasn't visible from below.