Use the
Right
Fastener
Each Type of
Deck Has Its Own
Requirements
by Stan Choiniere
I
n commercial construction, the right
tool can make the difference between
success and failure. The same is true
in low-slope commercial roofing applications; the correct fastener can make the
difference between a long-lasting installation or one that is plagued with constant
problems and poor performance.
There are several commonly used deck
types in commercial construction. Each has
its own unique set of structural characteristics, and each requires specific fastener
30
RoofingContractor June 2009
types, some of which are unique, in order
to meet all of the needs of the roofing system.
Roofing fasteners have only been on
the market since the mid 1970s when they
were first used to attach insulation. However, there were not any fasteners specifically engineered for roofing applications
until Factory Mutual created the need
for them in the late 1970s. In those days,
issues such as pullout, backout and corrosion resistance requirements were not
understood and, consequently, fastener
performance was not always up to the task.
As fastener manufacturers began to work
closely with roofing systems manufacturers, applying what they experienced in the
real world and learned through testing at
Factory Mutual, roofing fasteners became
significantly more sophisticated, as well as
deck and task specific.
Originally, steel and wood were the
only deck types that were acceptable for
mechanically attaching insulation or mem-
Use the
Right Fastener
n Each type of deck requires its own specific types of fasteners, some of which are unique, in order to meet all of the needs of the roofing system.
(Photos courtesy of OMG Roofing Products.)
brane. Structural concrete, lightweight insulating concrete, gypsum and cementitious
wood fiber decks such as Tectum® had
unique properties that prevented roofing
components from being attached with traditional screws. As fastener manufacturers
started to see these opportunities in the
roofing industry, they dedicated significant
resources, designing specific fasteners to
meet commercial roofing demands as they
were understood at the time. At the same
time, new fastener companies emerged
that were solely dedicated to the commercial roofing industry, and several new
fasteners were developed with improved
32
RoofingContractor June 2009
performance on conventional roof decks
as well as on decks that would not accept
traditional screws. Many innovative ideas
and designs were developed as a result of
this situation. Some became very successful and resulted in patented designs that are
still in use; others, while interesting, never
made it past the prototype stage.
Today, there is a wide range of fastener
options available in the market for every
application. Outlined below is a generic
description of the most common decks and
fastener options as they currently exist.
Steel Decks
Without question, steel decks are the
most commonly specified roofing substrate
in the market. It’s available in several different configurations, gauges, and tensile
strengths, all of which plays a major role in
fastener performance. In fact, when a screw
pulls out of a steel deck it’s the deck that
fails, not the screw.
When Factory Mutual changed the wind
uplift test frame from 5 feet by 9 feet to
12 feet by 24 feet for all mechanically
attached systems over 4 feet wide and for
fully adhered, built-up and modified bitumen systems that required wind ratings
of over 90 psf, the limitations of many of
Use the
Right Fastener
n Figure 1. Fasteners used for membrane attachment generally feature a buttress tread design where
the angles of the tread are not the same on the top and bottom plane.
pose” fasteners are also available that can
enhance pullout in wood decks. The pullout
resistance of dimensional lumber is generally fairly good due to the thickness and
density of the material. However, achieving
consistent or adequate pullout values can
be difficult in plywood and OSB, especially
when it is less than three-quarters of an
inch thick. This is due to the limited thread
engagement as well as voids in the laminations. Where wind loads are dynamic, especially in mechanically attached single-ply
applications, this can be a great concern.
Fastener manufacturers continue to search
for an affordable fastener design that will
accommodate plywood and OSB decks.
Cementitious
Wood Fiber Decks
n Figure 2. Heavy-duty screws with a symmetrical thread design are common in structural
concrete applications.
the screws used in steel became clear. As a
result, there are several types of screws specifically designed and engineered for steel
deck applications today.
The insulation or membrane being
attached determines which specific fastener is used in steel deck applications.
“Standard” screws, often referred to as No.
12s, are typically used to attach insulation,
while larger diameter screws (No. 15 and
No. 21) are used to attach membrane. Larger diameter fasteners used for membrane
attachment generally have a buttress tread
design where the angles of the tread are not
the same on the top and bottom plane and
point configurations that maximize pullout
and back-out resistance. (See Figure 1.)
Insulation attachment is less dynamic
than membrane attachment, and insulation
fracture is more likely to occur than fastener
pullout so insulation screws are less sophisticated. However, in both membrane and
34
RoofingContractor June 2009
insulation applications, all of the fasteners
are used in conjunction with a stress plate
designed for the specific application.
Most roofing system manufacturers have
fastener programs and generally require
their fasteners to be used to meet warranty
requirements. Approvals, especially Factory
Mutual approved systems, have minimum
deck requirements, therefore the roof cover
manufacturer must be consulted for specific deck and fastener requirements.
Wood Decks
Dimensional lumber, plywood and OSB
are all typical wood decks. Currently there
are no roofing screws designed specifically
for these materials. Instead, the common
practice is to use steel deck screws, especially “standard” screws.
Fasteners with coarse thread designs
generally provide the best pullout resistance
in wood. Heavy-duty No. 14 or “all-pur-
Cementitious wood fiber (CWF) decks
are not capable of holding a “traditional”
screw. The wood fiber and cement construction are not dense or stable enough to hold
small diameter shallow thread screws.
Many years ago, the common practice
was to use quarter-inch diameter toggle
bolts in long lengths with 4 inches of thread
to attach insulation and membrane to these
types of decks. While this was a good solution, it was highly labor intensive and not
very economical.
As an alternative, fastener manufacturers developed large diameter, coarse thread,
auger-type fasteners made from materials
such as glass-filled nylon. These engineered
fasteners were designed to accommodate
the varied density of CWF decks and could
often be installed without pre-drilling; however, the more dense CWF decks do require
pre-drilling.
Some of these fasteners are made with
anti-backout mechanisms for mechanically
attaching membrane. In addition to glassfilled nylon fasteners, there are others on
the market made of steel that look like
monster screws.
Also common for CWF decks are nontraditional fasteners, particularly for attaching base sheets. These hammer-in or drivetype fasteners have barbs that extend into
the deck after the fastener is seated and
provide an excellent attachment method.
Having a qualified technician perform pullout tests is a must with this type of deck.
Use the
Right Fastener
n Left: The insulation or membrane being attached determines which specific fastener is used in steel deck applications. Standard screws are typically
used to attach insulation in steel deck applications. Right: With lightweight insulating concrete installed over a steel form deck, the membrane can be
fastened directly to purlins. Special purlin fasteners with drill points and fine threads may be required.
Gypsum Decks
As with CWF decks, gypsum decks
will not hold a traditional fastener.
While many heavy-duty fasteners have
achieved relatively high initial pullout
resistance values in gypsum decks,
those values greatly diminish over time
as insulation or roof cover movement
works the screw back and forth in the
setting. Gypsum decks are not resilient
enough to take this movement and the
integrity of the pullout resistance values
drop dramatically.
Many large diameter, glass-filled
nylon auger-type fasteners used for
CWF decks can also be used in gypsum
decks. Generally speaking, you have to
pre-drill gypsum decks before these fas-
teners can be installed.
In addition, non-threaded drive-style
fasteners can also be used to attach
base sheets to gypsum decks. These
fasteners are typically installed with a
weighted “pogo” driver. As with CWF
decks, you should always have a qualified technician perform pullout tests
with type of deck.
Save up to 50% in labor and expense with REX™ SynFelt.
REX™ SynFelt is a high-strength woven synthetic roof underlayment.
It is slip-resistant, stronger than felt and won’t tear off or buckle
when wet. REX™ SynFelt stands behind its product with a
25-year warranty. Ask for it by name.
301 South Blanchard Street | Valdosta, GA | 866-312-1837 | www.alphaprotech.com
36
RC04094Alpha.indd 1
RoofingContractor June 2009
3/13/09 2:46:41 PM
Use the
Right Fastener
Lightweight Insulating
Concrete Decks
Depending on mix design and condition of the existing deck, density
is all over the scale when it comes to
lightweight insulating concrete (LWIC)
decks. Material curing also affects both
the amount of force needed to install a
fastener as well as the pullout performance. In some cases, a drive type fas-
tener typically with barbs can be used to
attach insulation.
Using steel deck screws in these types
of decks has also become fairly common,
especially in high-wind applications. For
this application the screws are driven
through the LWIC into the steel form deck,
which helps to hold the LWIC in a “sandwich” between the steel deck and the insulation board.
n Fasteners are often used in conjunction with a
stress plate designed for the specific application.
TM
Construction Managment Software as a Service
However, it is more common to attach a
base sheet to this type of deck. Base sheet
fasteners formed from light-gauge steel
have been used to attach base sheets for
over 20 years and have proven their worth
in high-wind areas such as South Florida
where LWIC is common. Insulation and or
additional plies can then be mopped in or
adhered with insulation adhesive and an
adhered single-ply, built-up or modified
bitumen system installed on top.
Seldom are single-ply systems mechanically attached on LWIC unless there is
a steel form deck under the LWIC that is
capable of providing adequate pullout
resistance or unless the membrane can be
fastened directly to purlins. When attaching directly to purlins that are heavier than
18 gauge, special purlin fasteners with drill
points and fine threads are required.
The auger-style fastener discussed earlier is not acceptable for use with lightweight
insulating concrete decks. Additionally,
these decks also require tests to determine
the specific pullout values.
Structural Concrete Decks
When it comes to structural concrete, roofing contractors have many different fastener
options, as both insulation and membrane
can be installed with strong pullout values.
Regardless of what fastener you select
for the job, you must pre-drill the deck, so
installation is labor intensive. Heavy-duty
screws with a symmetrical thread design
are common in this application. (See Figure
2.) Unlike the buttress thread, symmetrical
threads have matched angles on the top and
bottom of the thread and cut cleanly when
RC06094ACLY.indd 1
38
RoofingContractor June 2009
5/1/09 10:22:09 AM
Use the
Right Fastener
properly heat treated and installed into a
properly sized pre-drilled hole. Installing
screws into structural concrete requires a
good-quality, high-torque screw gun and a
little more time and finesse but they can be
backed out if necessary. As drill bits wear,
the hole gets smaller and the fasteners
become harder to install, so it’s imperative
that the drill bit be replaced frequently on
these projects.
However, drive-type fasteners have
become a more popular choice for structural concrete decks. Concrete fasteners, as
they are known, typically have a deformed
shank that, when driven into a properly
sized pre-drilled hole, creates an interference fit providing very high pullout resistance. While these drive-type fasteners are
relatively easy to install, they are very difficult to remove. Regardless of whether you
are installing a screw or hammer-in fastener, it’s important to pre-drill holes a minimum of a half-inch deeper than fastener
embedment in order to accommodate the
debris that falls back into the hole when
the fastener is installed. Testing the pullout
values on these decks is also a good idea in
order to determine the proper hole size for
maximum pullout performance and installation ease.
Adhesive fastening systems have also
become common for installing insulation
on structural concrete decks, as well as on
some gypsum, lightweight insulating concrete and cementitious wood fiber decks.
Material costs are higher but labor is significantly reduced.
Lastly, when it comes to re-roofing, it is
important that the deck and insulation is
dry. Any moisture trapped under a new roof
will work to accelerate the corrosion process. Corrosion-resistant fastener coatings
are highly engineered today. The industry
has transitioned from “sacrificial” to “barrier” coatings. Sacrificial coatings react
with corrosive elements and, as their name
implies, sacrifice themselves to protect the
base material. Eventually, however, the coating is depleted and the base material (i.e.,
the steel) is exposed to the moisture, which
quickly consumes the steel. Depending on
the corrosive, the sacrificial layer depletes at
different rates. By contrast, barrier coatings
form a protective layer between the potential
corrosive and the steel. Since these coatings
are not consumed, they provide longer corrosion resistance against more potential corrosives as well.
Fasteners are a key component of nearly
every type of roofing system. Proper selection is imperative if the system is to perform
to its full potential. It is very important to
work closely with the roof cover manufacturer to make sure that you not only have
the right fastener but that you also have
the correct stress plate and that you are following their specific fastening patterns and
installation procedures. Doing so will help
to ensure that the roof performs as intended for years to come.
Stan Choiniere is National Technical Manager, OMG Roofing Products, Agawam,
Mass. For more information, visit www.
olyfast.com.
Premeasured.
Prefabricated.
Pre-engineered.
At Duro-Last®, we sweat the details.
You get the credit.
Each Duro-Last® roofing system is precision-fabricated to
perfectly fit the building it’s designed for, right down to the
stacks and flashings. Duro-Last works with you every step of
the way to make sure your Duro-Last roof is delivered to the
job site on spec, with all components included, and up to 85
percent of the seaming completed in our factory. That means
you can install faster with less labor, in all kinds of weather,
with less chance for callbacks. Best of all, the proven performance
of a Duro-Last roofing system will continue to deliver value
to your customers for years to come, with significant energy
savings, little to no maintenance, and the best warranties in
the business.
If you want to satisfy your customers and build your
business, it’s no sweat. Install the precision-fabricated
roofing system: Duro-Last.
To find out more, call us or visit
www.duro-last.com/top
and request our free brochure.
800-248-0280 • www.duro-last.com
“Duro-Last” and the “World’s Best Roof” are registered marks owned by Duro-Last Roofing, Inc.
RC04094Dula.indd 1
3/5/09 1:12:12 PM
www.roofingcontractor.com
39