Eliminating Shingle Callbacks

May 15, 2003

May 2003 Interface • 15
Proper shingle application often means the difference
between a profitable job and one that is not! The experienced
applicator usually is able to apply the shingles more
quickly than one who isn’t. The challenge to the applicator is to
understand the fundamentals of shingle installation
and ensure that they are met or exceeded.
Otherwise, the risk of callbacks is as certain as is
the reality of an unhappy owner.
Two major areas of application concern are those
of flashing and fastening. Improper flashing often
results in a leak at the first rain, while improper fastening
might take longer for the shingle(s) to be
blown off and leak. The best way to avoid these problems
is for the installer to follow published industry
application procedures, as outlined by the shingle
manufacturer and referenced within the application
manuals of the National Roofing Contractor’s
Association (NRCA) and the Asphalt Roofing
Manufacturer’s Association (ARMA). Unnecessary
callbacks can be best avoided by complying with
these key roofing practices.
Proper flashing incorporates the use of an appropriate
underlayment felt, correctly installed over the
entire roof deck. In many areas of the country, good
roofing practice (and building codes) require a selfadhering
membrane (ice and water shield) be used
on key areas of the roof. To prevent the occurrence of leaks, use a
self-adhering membrane on roof areas where there is a possibility
of ice and snow accumulation. Areas that can be troublesome are
along the eaves, valleys, roof penetrations, and behind chimneys
that interrupt the plane of the roof. These problems also can
occur in certain southern areas of the country, where the buildup
of pine needles and leaves can cause a water dam, and the resulting
back-up of water may result in a leak.
Valleys are critical since water flows from both intersecting
roof planes, channeling into the valley area. A self-adhering membrane
must be run through the center of the valley, with additional
widths added to either side to a point at least 36″ from the
Figure 1: In many areas of the country, good roofing practice (and the building
code) requires a self-adhering membrane be used on key areas of the roof.
16 • Interface May 2003
valley centerline. When joining rolls of self-adhering membrane,
the sides should be overlapped a minimum of 2″ to 4″. When running
the underlayment felt to the valley, it is best to overlap the
self-adhering membrane a minimum of 12″.
Another major area of concern is the flashing used
along the vertical side walls of chimneys, dormers, etc.
As shingles are individual units, they must be flashed
with individual pieces of metal, referred to as “step
flashing.” This is necessary because a continuous piece
of flashing could not adapt to the changes in thickness
encountered on succeeding shingle courses and would
leak. Also, the use of roof cement with continuous
flashing will only delay the leak until later. However, the
use of roof cement can be helpful when used with step
flashing on lower slopes (2:12″ to 4:12″) to assist with
keeping water from running in behind the flashing.
Chimneys, which are usually set on a different
foundation from the rest of the structure, require flashing
that will accommodate a certain amount of movement.
Leaks will occur when flashing can not adjust for
this movement. Chimneys that are adjacent to the roof
require step flashing at the point where they tie into the
shingles on the roof. Chimneys that are in the field of
the roof also require the use of step flashing as well as
installing a cricket on their high side to divert the flow
of water to either side. Use of a self-adhering membrane
as a secondary protection system in these areas is
important to help prevent leaks caused by a backup of
Improper flashing of skylights also can result in
leaks. The skylight must always be installed on curbing high
enough to allow the use of “step flashing” along its sides and a
cricket on its high side. As with other flashing details, the use of a
self-adhering membrane along the skylight will help to keep it
Proper fastening is also important in order to prevent callbacks,
since it is essential to the shingle’s ability to resist being
dislodged or blown off by the wind. Proper fastening is easily
observed or measured. Manufacturers print a set of application
instructions on each shingle wrapper, and most use diagrams that
specify the correct fastener location. The way many contractors
increase their profitability is to quickly apply the shingles, thus
reducing installation time. Because of this, the installer is usually
paid by piecework, often resulting in hurried application, inattention
to detail, incorrect fastener location, and too frequently, a
missing fastener.
While pneumatically-applied fastening (whether nails or staples)
increases the speed of installation, the technique can create
callbacks if not used properly. The key with any pneumaticallyapplied
fastener is to have the gun’s pressure set properly and to
drive the fastener flush with the shingle’s surface as it sits tightly
to the deck. This becomes difficult when over-roofing a surface
that has started to curl and cup or where the new shingle is not
as thick as those used on the first roof. Care must be exercised
when re-roofing, as surface irregularities will complicate pneumatic
fastening. The gun’s pressure also needs to be adjusted as the
shingle’s temperature changes, so as not to under or overdrive the
Staples can be effective when properly applied, but problems
are created when applicators take short cuts. The most common
misapplication is when the staple’s crown is not applied parallel
Figure 2: As shingles are individual units, they must be flashed with individual
pieces of metal, referred to as “step flashing.”
May 2003 Interface • 17
to the shingle’s length, but rather in an arc. As the staple arcs,
the leg rather than the entire crown becomes the leading holding
point, which is not enough holding power to resist shingle blowoff.
Since this was a common occurrence, the pneumaticallyapplied
nail has almost entirely replaced the staple today.
When installing a laminated shingle, it is very important
to place the fastener so it penetrates both the overlay and the
underlay portion of the shingle. Most manufacturers place a
visible fastening line on each shingle to indicate the correct
location for the fastener. This is even more critical on steeper
slopes where the underlay portion could slip off the roof if not
fastened securely.
To further increase the speed of application, some
installers “rack” or apply the shingles straight up the roof.
This practice reduces the amount of lateral effort required,
thus speeding up the installation. The danger from racking is
that when the installer feeds in the next row of shingles, he
does not raise the covering tab and nail into the end of the
inserted shingle. As a covering tab occurs in every other row,
the result is usually one missing nail in one out of two shingles.
In addition, on steep slopes or in high wind areas, good
roofing practice requires that six, rather than four, fasteners
be used per shingle.
Fastener location is also very important. If the fastener is
too far left or right it could line up in the cutout area of the shingle
in the succeeding row and be exposed to the weather, and
eventually leak. If it is too low, the fastener will be exposed, and if
too high, it could interfere with the shingle’s ability to seal properly.
Additionally, with high-nailing, the added wind leverage on the
tab could reduce its wind resistance. If the fasteners are so high
that they miss the underlying shingle entirely, potential damage
from wind is greatly increased since only four fasteners penetrate
each shingle rather than the eight penetrations that normally
Once again, shingles are individual units and not a waterproof
membrane. As the slope of the roof decreases, the ability of the
shingle to shed water is also reduced. Longer runs of roof area
also hold more water on the roof surface, further reducing the
roof’s ability to
perform its water
shedding function.
Therefore, as the
roof slope decreases
and the run or
length of the roof
increases, the use
of proper flashing
details and correct
fastening become
even more critical.
Callbacks are
never profitable
and must be
avoided. As a rule
of thumb, all penetrations
changes in the
plane of the roof
can and often do
result in a leak. To prevent leaks, all details must be adequately
flashed to be watertight. Inattention to these details often results
in time-consuming investigation and repair, a non-profitable callback,
and most importantly, a dissatisfied owner. 
Raymond L. Corbin is the President
of Corbin Roofing Systems. He has
been the Director of BURSI for Johns
Manville for 19 years. Ray holds four
United States roofing shingle design
and application patents. He has been
an industry member of RCI since
1985. Mr. Corbin was honored with
the Richard Horowitz Award for excellence
in technical writing for Interface
in March 2003.
Figure 4: The fastener must catch the top edge of the underlying shingle.
Figure 3: When installing a laminated shingle, place the fastener so that it penetrates both the overlay and the
underlay portion of the shingle.