Reasonable Intentions And Installation Temperatures; A Cautionary Tale

May 15, 2006

The following story describes an event
with less than desirable consequences. An
effort has been made to make this article
more practical than scientific, the idea
being that similar consequences could easily
be avoided by remembering the steps that
led to this unique problem and not repeating
them. It is important to remember that
the conditions described are not unique to
any particular manufacturer.
The problem
A project manager
called our offices to say
that extruded polystyrene
insulation that
had just been installed
on a re-roof project had
begun to lift and warp.
He felt that the manufacturers
of the products
being installed
should be advised. He
noted he didn’t know
what was causing the
problem, but that he
would like immediate
assistance to help determine
its cause, as
he claimed he had “never
seen anything like
Arrangements were
made to visit the project
site the next day.
Photos were taken, site
personnel were interviewed,
and samples of
damaged insulation were obtained in the
event that lab testing would be required.
The conditions
The words “lift” or “warp” do not adequately
describe the condition of the insulation.
It was curled similarly to potato chips.
The curling was so pronounced that the
deformation dislodged the 1/2-inch, glassfaced
gypsum coverboard that had been
installed with low-rise foam adhesive. Its
movement in one location had pulled apart
torched-down, modified-bitumen side laps.
Roof system assembly
The roof assembly was as follows: a
metal deck; 15# felt; 5/8-inch, Type X gypsum
board; a base layer of extruded polystyrene
insulation; a tapered, extruded
polystyrene insulation, 1/2-inch, pre-
Wrinkling and curling in the EXPS-tapered roof insulation below the 1/2-inch, glass-faced gypsum
A U G U S T 2006 I N T E R FA C E • 3 5
primed, glass-faced gypsum
coverboard; and one layer of
smooth (black), APP-modified
bitumen. Another layer of
granulated, APP-modified bitumen
was to be installed later.
The 15# felt, gypsum
board, and base layer of extruded
polystyrene were mechanically
fastened to the metal
deck with metal screws and
Subsequent layers of
tapered extruded polystyrene
insulation and the top layer of
1/2-inch, pre-primed, glassfaced
gypsum coverboard were
installed utilizing low-rise
foam insulation adhesive.
The same system with the
same materials had been
installed recently without any
problems on another project. The only difference
was that on the previous project,
the deck was concrete.
The current project included an adjacent
building on which the same system had also
been installed, using materials from the
same shipment without problems. That
adjacent building also had a concrete deck.
A urethane insulation adhesive manufactured
by a different company was utilized to
secure the tapered insulation system.
The materials used in the project
appeared to be compatible, based on manufacturers’
product descriptions and actual
field experience.
Installation procedure
There was nothing unusual about the
installation procedure, either. However,
because the weather forecast reported a
possibility of isolated showers in the nearby
hills, the roofing crew had covered the first
layer of APP-modified bitumen with looselaid,
black polyethylene sheeting (Visqueen
™) so that they could continue installation
the next morning without waiting for
the roof to dry. The crew scattered unopened
rolls of modified bitumen membrane
randomly on top of the polyethylene.
Jobsite observations
1. Only tapered panels were warped or
2. No damage to the fill boards or base
layer insulation was observed.
3. No damage to mechanically fastened
insulation was observed.
4. There was adhesive on unaffected
filler board insulation.
5. There was adhesive still in place on
undamaged filler board under dam-
36 • I N T E R FA C E A U G U S T 2006
Left: An overview of an area
where the reaction to heat
build-up occurred.
Below: The curling was so
pronounced that it dislodged the
1/2-inch, glass-faced gypsum
coverboard that had been
adhered with urethane adhesive
to the top layer of the EXPS.
aged tapered insulation.
6. There was adhesive on damaged
tapered insulation.
7. No evidence of incompatible chemicals
or materials was found.
8. The damaged insulation changed
shape but seemed to generally
maintain its manufactured mass
and thickness.
So what caused the tapered extruded
polystyrene insulation to change shape,
and could it reoccur?
Extruded polystyrene manufacturers
call for their insulation to be protected from
temperatures anticipated to exceed 165˚F.
They require extruded polystyrene insulation,
when stored, to be protected from
solar loading by covering it with a light-colored,
opaque material.
Installation instructions for EPDM-ballasted
roof systems that utilize extruded
polystyrene insulation require the immediate
application of ballast to completely cover
the black membrane to help prevent high
temperatures due to solar loading. Solar
loading can cause the temperature of black
EPDM to exceed 180˚F.
It seems reasonable to believe that black,
smooth, APP-modified bitumen could reach
similar temperatures due to solar loading.
However, based on previous field experience
and because the extruded polystyrene was
A side view showing the profile of a lifted area prior to roof cuts for visual observation.
A U G U S T 2006 I N T E R FA C E • 3 7
covered by a layer of 1/2-inch, glass-faced
gypsum coverboard, it was not anticipated
that solar loading would be sufficient to
affect the extruded polystyrene insulation.
The only variable was the black polyethylene
sheeting laid over the roof to keep
its surface moisture-free. This appears to
have prevented the dispersion of solar-generated
heat, and thus, allowed the tapered
insulation to reach temperatures in excess
of the recommended service temperature.
The manufacturers of the roof system
components were all saying, “Not me, not
me.” And, of course, they were right. The
problem was not manufacturer-specific.
Consequently, the project manager
decided to build a small model of the roof
assembly using leftover materials. He put
the model together and set it out in the sun
at approximately the same time of day as
when the black polyethylene sheeting had
been installed. The next morning they
found that the same warping of the tapered
insulation had occurred on the model.
Putting a temporary covering over the
modified bitumen to keep it dry may seem
like a good idea, but the side effect of trapping
solar-generated heat can be disastrous.
It is always a good idea to pay attention
to the temperature limitations of products
that are part of the design; one never
knows when they will become important to
the system.
Jeff Cramer started working in the roofing industry in 1975.
He is a member of RCI and has been a Registered Roof
Consultant (RRC) since 1994. He is currently an independent
sales representative for several commercial roofing material
manufacturers in central California.
Jeff Cramer, RRC
Carlisle SynTec Incorporated, a worldwide leader in
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positions nationwide. Join the Carlisle SynTec team and
experience rewarding opportunities and growth in the
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The position involves managing and directing the sales
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Managing, supervising and directing Carlisle sales efforts
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Candidates must possess a bachelor’s degree, 5 years of
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Carlisle SynTec Incorporated offers a competitive
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Carlisle SynTec Incorporated, visit the Web site at www.
Please send or email your resume to:
Carlisle SynTec Incorporated
P.O. Box 7000 • Carlisle, PA 17013
Carlisle SynTec Incorporated, a worldwide leader
in single-ply roofing technology, has openings for
Field Service Representatives. If you are interested
in exploring new opportunities and growing with
a reputable corporation, join Carlisle SynTec
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Applicants must possess excellent communication
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A bachelor’s or associate’s degree and 2 years
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years roofing/construction experience is required.
Basic computer skills are necessary.
Carlisle SynTec Incorporated offers a competitive
benefits package, including 401k, medical/dental/
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holiday and vacation pay. For information about
positions with Carlisle SynTec Incorporated, visit
the Web site at
Please send or email your resume to:
Carlisle SynTec Incorporated
P.O. Box 7000
Carlisle, PA 17013
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38 • I N T E R FA C E A U G U S T 2006