Roof Decks A to Z Part 19: Fiber Reinforced Polymer (FRP)

ROOF Decks A to Z

THE STRENGTH AND versatility of fiber-reinforced polymer (FRP) have
long been recognized for concrete repair,
such as in parking deck rehabilitation (Fig. 1)
and bridge pier wrap. Moreover, FRP can be
fabricated into structural framing shapes,
industrial grating, cable trays, channels, angles,
tubes, and rods. These varied shapes are called
pultrusions, which is a blended word derived
from pull and extrusion (this is in contrast with
ordinary extrusions that are “pushed” through
the shaping dies or tracks).
FRP enjoys good fire resistance and flame
spread ratings. Review of product literature
indicates a flame spread rating of 25 when
evaluated by ASTM E841 (broadly known
as the Steiner tunnel test). FRP decking
is often used in paper mills, natatoriums,
food processing facilities, animal rendering
plants, textiles, fertilizer production and
storage, metal treatment, and similar highhumidity
or corrosive environments.2 It is a
good replacement selection for rotted wood
decks and deteriorated/spalling concrete
planks. Figure 2 depicts a decades-old
built-up roof (BUR) and FRP deck in a corrosive
Roof Decks A to Z
Feature
Part 19: Fiber-Reinforced Polymer (FRP)
By Lyle D. Hogan, F-IIBEC, PE, RRC
Interface articles may cite trade, brand,
or product names to specify or describe
adequately materials, experimental
procedures, and/or equipment. In no
case does such identification imply
recommendation or endorsement by
the International Institute of Building
Enclosure Consultants (IIBEC).
environment with stainless steel decking as
the replacement deck in this instance.
The decking product is addressed under
ASTM D3841.3 That standard mostly concerns
itself with classifying FRP products according to
flammability and dimensional tolerances. But
beyond this, good information (that is, white
papers, research, testing standards, project
profiles, and the like) is quite sparse for FRP as
a substrate for commercial low-slope roofs; the
reader will encounter this with a simple web
search for “FRP roof decking”—or anything
remotely similar. Being a specialty product,
FRP occupies a small slice of the commercial
low-slope roof deck market. But such decks do
exist, and the building enclosure consultant
would do well to recognize when they are
encountered.
The decking gains stiffness from bidirectional
arrangement of glass reinforcement, which
usually constitutes about half of the product
weight. In contrast with exposed FRP panels,
roof deck products do not need a UV-stabilized
resin or coating. Resin binding the glass fiber
core is either isophthalic polyester or vinyl
ester; while both provide outstanding corrosion
resistance, vinyl ester is the widely preferred
resin in environments having elevated operating
temperatures.4
CONSIDERATIONS DURING
ROOF SYSTEM DESIGN AND
SELECTION
FRP is considered a “nailable” deck, meaning
it can be mechanically anchored to support
framing and it can receive fasteners for
membrane and insulation. Yet, because it is
likely to be found in high-humidity or corrosive
environments, the use of modern adhesives
Figure 1. The strength and versatility of fiber-reinforced polymer have long been recognized.
Here, carbon-fiber wrap is being deployed during extensive repairs to a parking deck.
This is 19th in a series of articles examining
various deck types. While used in siding/cladding,
as exposed corrugated roofing sheets, and as
form deck for poured concrete, this article will
concentrate on fiber-reinforced polymer (FRP) as
the substrate for low-slope roofing.
16 • IIBEC Interface November 2024
should be considered when selecting the roof
assembly. Adhesives would sidestep concerns
for eventual fastener corrosion or enlarging of
the openings where membrane and insulation
fasteners penetrate.
Conventional threaded deck screws can
secure membrane and insulation materials, but
fracturing of the deck can sometimes occur if
these “fixings” are overdriven (Fig. 3). Toggle
bolts require predrilling, but they are prone to
losing preload over the service life—such as
when securing nailers or anchoring the flanges
of a rooftop curb. Splitting-shank rivets are
approved for this application and are preferable.
A vapor retarder is also likely to be a
component in FRP construction because of some
environments listed above. Forty years ago,
kraft paper might have been applied directly
to a steel deck in bituminous adhesive (Fig 4).
The vulnerability to puncture is clearly evident,
and many such vapor control layers were often
damaged before insulation was even installed.
A thin layer of hardboard installed prior to vapor
retarder application can allay this risk.
Modern adhesives lends themselves to
remaining layers and components. Indeed,
an entire plausible roof assembly could be
Figure 2. Old built-up roofing and decades-old fiber-reinforced polymer deck in a corrosive
environment being replaced here with new stainless steel decking (Image courtesy of Teamcraft
Roofing, Salisbury, NC).
Figure 3. Threaded deck screws can secure membrane and insulation materials, but fracturing of the deck can sometimes occur if these “fixings”
are over-driven. Toggle bolts will require predrilling, but they are prone to losing preload over the service life. Splitting-shank rivets are approved
for this application and are preferable (Image courtesy of Teamcraft Roofing, Salisbury, NC).
November 2024 IIBEC Interface • 17
configured using no fasteners at all—other
than those used to anchor FRP deck panels
to structural supports and the related sidelap
stitching screws.
From casual viewing, FRP can be deceptively
similar to conventional painted steel decking.
During underside evaluation of an existing roof,
be alert for minor differences that will assist in
correct deck identification. Close scrutiny (using
binoculars if necessary) will reveal that FRP has
more rounded rib edges than the angular edges
of a steel deck’s ribs. Moreover, rib/flute depth
is likely to deviate from the ordinary 1.5 in.
(38.1 mm) dimension of most steel decking—
sometimes ranging up to 3.5 in. (89 mm). The
horizontal module may be different too, ranging
to 8 in. (203 mm) on center. Misidentifying FRP
early on could spell embarrassment later in the
bidding and contracting phases of a project.
The evaluation phase offers opportunity to
explore for other matters of importance. The
old FRP deck shown in Fig. 5 had electrical
conduits improperly situated over the supports.
While certainly easier for the electrician, this
arrangement can create big problems for
mechanically attached roofs. High conduits
should always be located and considered prior to
roof system selection. Again, when encountered
with FRP decks, modern adhesives can be
deployed to address attachment of roof layers
and to avoid conflict/delays during construction.
Ordinary load/span tables are published by
respective vendors for sizing the module of
deck needed; notably, the values appear to be
predicated on the use of washers coupled with
fasteners that engage structural supports. But as
outlined above, roof decking is just one shape/
profile in a rather vast product line, so technical
inquires beyond printed span properties may
be met with frustration (as it was for the author
during development of this article).

CONSIDERATIONS DURING ROOF DECK
CONSTRUCTION

If threaded deck screws are to be used, ordinary
pull testing should be deployed to determine
the necessary spacing/pattern. Just as with
conventional steel decks, sidelap stitching screws
are necessary, and deck fasteners for membrane
and insulation (if used) should engage the
high rib. As outlined in Part 17 of this series,5
engaging the high rib can be a challenge when
installing tapered insulation, but it can be
managed with some forethought regarding the
board layout.
Framing for roof openings would be necessary
as in the manner of conventional steel decking.
Moreover, sump pans (or receiver pans) are
required for drain openings, and a continuous
shelf angle (or other appropriate support) should
be present at walls for the long dimension of
deck panels.
SUMMARY REMARKS
The foregoing discussion is offered as 1) a
spotter’s guide for correct deck identification
and 2) a baseline of issues to be considered
when dealing with this specialty deck type.
Again, FRP should not be mistaken for painted
steel decking, or when it is merely serving as
form deck for poured concrete—as well it might.
Vendors of FRP products are diversified
and manufacture quite a variety of shapes
and products to fulfill a host of applications.
And why not? Once in business for production
Figure 4. Forty years ago, kraft paper may have been applied directly to a steel deck in bituminous adhesive as the vapor control layer. The
vulnerability to puncture is clearly evident. Accordingly, a hardboard layer should first be installed over fiber-reinforced polymer prior to vapor
retarder application.
18 • IIBEC Interface November 2024
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IIBEC, IIBEC Interface,
434 Fayetteville St., Suite 2400,
Raleigh, NC 27601.
of fiberglass items, there are multiple viable
markets. But as suggested above, the paucity
of technical support for matters of commercial
low-slope decking may become evident. One
vendor offers a noteworthy clause stating that
FRP decking is not addressed by the governing
building code(s), so the ultimate responsibility
for and approval/acceptance rests with the local
building official or design professional.6
REFERENCES
1. ASTM International. 2024. Standard Test Method for
Surface Burning Characteristics of Building Materials. ASTM
E84-24. West Conshohocken, PA: ASTM International.
2. Toler, Tom. 2011.“FRP Roof Deck: A Solution for Challenging
Conditions.” Interface, November. Raleigh, NC: International
Institute of Building Enclosure Consultants (IIBEC).
3. ASTM International. 2021. Standard Specification for
Glass-Fiber-Reinforced Polyester Plastic Panels. ASTM
D3841-21. West Conshohocken, PA: ASTM International.
4. Personal communique with Mr. Aaron Barth, Sales
Director of Building Products, Enduro Composites
(April 11, 2024).
5. Hogan, L.D. 2022. “Roof Decks, A to Z: Conventional
Steel Decks, Part 17,” Interface, August. Raleigh, NC:
IIBEC.
6. Stabilit America. n.d. “Tred-Safe Deck.” Tech data
sheet. https://www.stabilitamerica.com/wp-content/
uploads/2021/08/Tred-safe-deck-tech-data-sheets.pdf
<accessed September 24, 2024>: p.2.
ABOUT THE AUTHOR
Lyle Hogan,
F-IIBEC, PE, RRC, is
principal of Fincastle
Engineering Inc.,
Greensboro, North
Carolina. He is a
registered engineer,
a Registered Roof
Consultant, a Fellow
of IIBEC, and an ICC
structural masonry
inspector. For nearly
45 years, Hogan has evaluated, designed,
and administered roofing projects in half
of the US using a variety of systems. His
technical articles have appeared in numerous
technical publications and conference
proceedings.
Figure 5. This old fiber-reinforced polymerdeck had electrical conduits improperly situated over the supports. Notice the line of sidelap stitching
screws and the specialty fasteners used to secure roof insulation (Image courtesy of Teamcraft Roofing, Salisbury, NC).
LYLE D. HOGAN,
F-IIBEC, PE, RRC
November 2024 IIBEC Interface • 19