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Field Performance of Spray Polyurethane Foam Flashings

May 15, 2004

6 • Interface April 2004
In September of 2003, The National Roofing Foundation completed
its second field study of Spray Polyurethane Foam (SPF)
roofing systems. The study, which began in 2001, examined
188 SPF roofs of various sizes and shapes. The roofs ranged in age
from new to 31 years, with an average age of 11.75 years.
This study was a follow up to the original study completed in
1998, which examined performance characteristics of in-place SPF
roofs. While the first study dealt with physical properties of the
aged roofs, the second survey was chartered to determine the viability
of the SPF material as a flashing material over a wide range of
Unlike other roofing systems, the mechanic applying SPF materials
literally goes up the wall, curb, or roof-mounted penetrations.
Flashing sheets and fasteners are not required. The NRCA Manual
of Roofing and Waterproofing Construction Details calls for the use of
metal counterflashings. The study examined what is actually happening
in the field with SPF flashing details that do not incorporate
metal flashings. Table 1 details the information for both the 1998
and 2003 study of SPF roofs.
While flashing details are the most likely cause of roof leaks in
virtually all roofing systems, they are often overlooked during the
membrane selection process by the roof owner and the consultant
or architect. Most conventional systems utilize metal, bituminous,
or polymeric membrane to solve a variety of flashing details.
Sometimes these materials are manufactured in the factory, and
sometimes the roofing contractor relies on experience to field manufacture
the proper solution to the problems.
All SPF details are essentially field manufactured. This allows
for an easier seamless transition around roof-mounted equipment,
parapets, and roof penetrations. The spray application allows for
thicker applications to slope away from potential leak problems,
such as walls or penetrations. After the application of foam, the
protective coating usually extends 4 to 6 inches up projections and
vertical walls.
A note of caution on thicker applications of SPF: industry standards
call for maximum lifts of 1-1/2 inches. When foam is applied
in thicker lifts, the exothermic reaction can cause thermal degradation,
creating poor cell structure and foam with low compressive
strength. Caution must still be
used when applying greater thickness
in multiple lifts as the heat
must be given time to escape.
Spray foam has the unique
ability to adhere to virtually all
exterior building materials.
However, certain non-ferrous metal
flashings should be primed prior to
application of SPF.
During the field study, we
learned that spray polyurethane
Phase I (1998) Phase II (2003)
Number of roofs in study 140 188
Oldest age of roof(s) 27 Years 31 Years
Number of recoated roofs 39 40
Percentage of recoated roofs in study 28% 21%
Average age of roof at recoat 11.3 Years 15.0 Years
Number of roofs of unknown age at recoat 11 3
Average age of all roofs 11.0 Years 11.75 Years
Table 1: Comparative Data on SPF Roof Studies
foam, when correctly applied to surfaces and then
coated, does not require metal counterflashings.
The survey examined roofs in California, Texas,
Wisconsin, Kentucky, Illinois, New Jersey, New
York, and Connecticut. SPF flashings, including
roof-to-wall, roof-to-roof transition, penetrations,
termination points, and equipment supports were
found to work well in each of these climates. The
National Roofing Foundation released the report,
“Performance of Spray Polyurethane Flashings” earlier
this year.
Following are pictures and descriptions of various
roofing details examined during the study.
Special thanks to the NRCA for allowing their reprint.
Standard Metal Counterflashing
Figure 1 shows a typical wall with SPF and coating applied up the
wall and covered by the metal counterflashing. Galvanized sheet metal
was formed and surface mounted with a drip edge. The use of metal
as a counterflashing is consistent with detail SPF-4, which can be
found in the 5th Edition of the NRCA Roofing and Waterproofing
Metal Roof Expansion Joint
Figure 2 shows how SPF flashing can be used with a flexible bellows
to handle differential and cumulative movement in a large metal
roof. Note that the elastomeric bellows has been anchored in SPF and
coated. This deck runs along a second-story wall that uses SPF as a
transition between roof and wall.
Roof to Short Wall Transition
Figure 3 illustrates how SPF can make roof transitions to a wall
along with a short transition to the adjoining lower roof. A light-gage
metal wall panel and cap previously formed this transition. This detail
was installed in 1977.
Left: Figure 1 – Standard metal counterflashing.
Below: Figure 2 – Metal roof expansion joint.
Figure 3 – Roof to short wall transition.
April 2004 Interface • 7
8 • Interface April 2004
SPF Roof to High Roof
A roof-to-roof transition is shown in
Figure 4 that details how SPF was used to
solve a difficult tie-in for two different
roof systems. The existing metal flashing
was covered with spray foam and coated.
The SPF transition detail also covers a
short wall that has metal panels and
window units. The SPF tie-in was
installed in 1991.
Interior Gutter System
A large existing warehouse complex
was re-roofed with SPF in 1991. The
existing metal roof and interior gutter
system were overlaid with 1.5 inches of spray polyurethane foam
and coating. All of the existing metal flashing system was secured
and covered with spray foam. No new metal flashing or counterflashings
were added. The interior gutters were also covered with
SPF as shown in Figure 5.
SPF Roof and Wall Transition
A complete roof and wall transition with SPF is shown in Figure
6. No metal flashing has been used on this 1997 installation. All of
the pre-existing metal flashing is now encased in SPF. No new metal
was used.
SPF Wall Flashing
The large lower main roof of this distribution center is broken
up by a three-story brick wall. As seen in Figure 7, the expansion
joint in the brick wall is active. The SPF re-roof covers all pre-existing
metal flashing. The SPF flashing
now reaches above the original metal
counter flashing. There are no cracks
or spalling of the SPF. The coating is
functioning as a counterflashing over
the SPF at the top of the pre-existing
SPF Low Wall Flashing
In some instances, walls may be
completely covered by the SPF system
with no adverse performance.
Figure 8 shows a low masonry parapet
wall and metal cap system with
SPF and coating in a 1998 installation.
Wall construction – especially
how moisture is handled from the
outside brick veneer – must be thoroughly
understood before covering
with SPF.
Equipment Support
Both low and high equipment
support curbs were observed as
shown in Figures 9 and 10. The high
curb appears to have been extended
up with a slightly smaller curb from
the original base (Figure 9) and flashed with SPF and coating. Low
curbs (Figure 10) were observed to have been treated the same way
with no functional difference, using SPF and coating. No metal
counterflashing was used, nor does it appear to be needed.
Above: Figure 4 – SPF roof to high roof
Right: Figure 5 – Interior gutter system.
Equipment Support Columns
SPF roofs were often found to have no need for pitch pans or for separating
support columns that are structurally sound and tied to a wall. Figure
11 shows a heavy steel support stand that is directly flashed with spray foam
and coating into the SPF roof/wall detail. The 1992 flashing installation
detail appears to be watertight and serving its intended purpose.
SPF Flashing
The NRF studies observed numerous flashing details where pre-existing
metal flashing had been installed. As shown in Figures 12 and 13, SPF can
easily adapt to many rooftop details by
being overlaid onto the existing prepared
substrate. Existing metal flashings
may remain and be totally
enclosed or left open as the need dictates.
Just as the Phase I study demonstrated
the performance value of SPF
roofing systems when properly applied,
Phase II has demonstrated that the use
of SPF as a flashing system easily
accommodates virtually all termination
details. The study specifically identified:
• Masonry units.
• Metal wall panels.
• Metal flashing of all types.
• Concrete pre-cast panels.
• Wood sheathing and board
• Asphaltic flashing systems.
• Single-ply flashing systems.
SPF may require primers when
applied over thermoplastic, single-ply
membranes. The use of a wash primer
is recommended when spraying over
Left: Figure 6 – SPF roof and wall transition.
Figure 8 – SPF low wall flashing application.
April 2004 Interface • 9
Below: Figure 7 – SPF wall flashing.
10 • Interface April 2004
It is important that all substrates receiving SPF should be
properly prepared, cleaned, (and, if necessary), primed. When
SPF is used as a recover over old membranes, it is important to
thoroughly examine the existing assembly. If edge metal is not
replaced, it may need to be reattached. Any wood nailers or
other materials that have surpassed their service life should be
removed and replaced.
The use of SPF and appropriate coatings were observed to
work quite well as singular flashing systems. The use of metal
counterflashing was not seen to be required as part of an SPF
roof system.
SPF as a flashing material in concert with an SPF roofing
system offers the following advantages:
• No seams or joints to allow for water penetration.
• No differential movement between materials.
Figure 9 – Equipment support – high curb.
Figure 10 – Equipment support – low curb.
April 2004 Interface • 11
• A fully insulating
system with no thermal
shorts to allow
energy transfer.
• Ability to conform to
any angle on penetrations,
or vertical
It is easy to envision a
future where this material
is used with conventional
membranes in a “hybrid”
system, allowing for the
benefits of SPF as flashing
material on roofs of other
types. This already is occurring
on liquid-applied coating
systems where
penetrations and terminations
are foamed, while the
field of the roof is coated. ■
1. Alumbaugh, R.L.,
“Maintenance of
Sprayed Polyurethane Foam (PUF) Roofing Systems,”
Proceedings of the Second International Symposium on
Roofing Technology, National Roofing Contractors
Association, Rosemont, Illinois, 1985, pp. 89.
2. Kashiwagi, D.T., “The Development of an Expert System
and Historical Database for PUF Roof System Specification,
Design and Analysis,” Proceedings of the Third
International Symposium on Roofing Technology, National
Roofing Contractors Association, Rosemont, Illinois,
1991, pp. 189.
3. Dupuis, R.M., “A Field and Laboratory Assessment of
Sprayed Polyurethane Foam Based Roof Systems,” National
Roofing Foundation, Rosemont, Illinois, 1998.
René M. Dupuis obtained his B.S., M.S., and Ph.D. degrees in civil engineering from the University of
Wisconsin at Madison. He has worked for the National Science Foundation, the University of Wisconsin, and
was also an assistant professor at the State University of New York at Buffalo. He is a professional engineer
and a principal and president of Structural Research, Inc., a consulting engineering firm located in Middleton,
Wisconsin. Since 1974, Dr. Dupuis has been involved in materials research with much of this effort devoted
to the roofing industry as a consultant. He has written and presented many articles and research reports on
roofing materials technology and has conducted numerous investigations for building owners, architects,
contractors, and manufacturers. Dupuis is a member of ASTM, CSI, NSPE, and ASCE. He is a member of the
CIB/RILEM International Committee on Single Layer Roofing; has served on the Roof Advisory Panel for the
DOE/Oak Ridge National Laboratory’s Roof Test Center; and as chairman of the Board of Regents for the
Roofing Industry Educational Institute (RIEI). He has served as technical advisor to the Midwest Roofing
Contractors Association (MRCA) and the National Roofing Contractors Association (NRCA) and as the ASTM
Task Group Chairman on Roof Performance. Dr. Dupuis received the James Q. McCauley Award from the MRCA and the
Distinguished Service Award from the University of Wisconsin at Madison College of Engineering in 1995.
Figure 11 – Equipment support with columns.
Above: Figure 12 – SPF flashing on a metal roof.
Figure 13 – SPF flashing, roof-to-wall.