Specifying SPF Roofing Systems
Spray polyurethane foam (SPF) roofing systems have been marketed for years primarily on their documented energy saving characteristics. Consequently much of the SPF roofing market has focused on property owners or institutions that pay their own energy bills. But what about property that is leased or rented, where the energy costs are transferred to the renter and not the owner of the building? Can SPF roofing systems be a cost effective alternative to membrane roofing systems over time without taking energy costs into consideration?
In today’s buildings industry, there is a growing desire to provide owners with cost effective durable, long-lasting roofing systems that combine high energy performance with low
maintenance costs. How do SPF roofing systems stack up against membrane roof systems such as modified bitumen, BUR and lower cost single ply membranes?
Life Cycle Cost Analysis
In order to answer these questions, in 2003 the Spray Polyurethane Foam Alliance hired Michelson Technology LLC to conduct a life cycle assessment of SPF roofing systems and compare them to conventional membrane insulated roofing systems. The study was conducted by Dr. Theodore Michelsen, former Executive Director of the Roofing Industry Educational Institute (RIEI), in which capacity he taught classes on Roof Asset Management and Life Cycle Costs. The study was conducted in accordance with ASTM Standard ASTM E 917 - 02 “Standard Practice for Measuring Life-Cycle Costs of Buildings and Building Systems”. It compared SPF roofing systems to membrane roofing systems in 6 different climate areas of the United States including upper state New York, central Florida, Ft. Worth, Texas, southern California,
Phoenix, Arizona, and Louisville, Kentucky.
The results show Spray Polyurethane Foam having a 30 year life cycle cost advantage over membrane roofs from a low of 12% using a 6 year recoat schedule to over 56% for a SPF system that is recoated on a 15 year schedule.
Dr. Michelsen assumed a membrane roofing system would require tear off and replacement in 10 to 15 years and the SPF roof system would be recoated to extend its service to at least 30 years. He added close to $1 per square foot for tear off of the membrane roof and $0.25 per square foot for added insulation.
For the study period Dr. Michelsen chose a 7% discount rate and 3% inflation. He assumed the existing roof system would remain in place and that the new roofing systems would include the installation of an R 5 of insulation.
Dr. Michelsen included an energy saving cost benefit for reflective coatings in his final conclusions. For the purpose of this paper, the cost saving benefit has been deducted
Table 1: Cost of SPF Roofing System Compared to Membrane over 30 years (2003 Dr. Michelsen study modified to eliminate energy saving benefit of reflective coatings) (20,000 sq ft Roof) Southern CA Cost of roof system over 30 years Full Cost After Inflation Initial Cost /sq. ft. Coating Cost /sq. ft. Tear-off & Replacement 1” SPF w/15 Yr. Re-coat $89,124 $150,158 $3.15 $1.52 N/A 3 Ply BUR 10 year system (R 10 fiberglass) 89,681 $150,664 $1.25 N/A $2.25
(N/A = not applicable)
As can be observed from the chart even with the energy benefit deducted, the SPF roofing system recoated every 15 years is still less costly to install and maintain than a very low cost membrane roofing system. But are the costs determined by Dr. Michelsen valid today? What About Today’s Costs?
Dr Michelson’s life cycle assessment was conducted over 7 years ago. Building material costs have increased significantly in the interim due to raw material shortages and increased
international demand from Asia and Europe. How have costs changed in the interim? In order to determine if Dr Michelson’s conclusions can be supported in today’s market; the author compared prices reported in the 2009 edition of the National Construction Estimator by Dave Ogershok & Richard Pray published by Craftsman Book Company of insulated membrane roof systems to equal R value SPF roof systems. The author validated the prices reported in the “Estimator” by a survey of roofing contractors in California.
(Note: The costs listed in the “Estimator” do not include profit, overhead, local permits, bid bonds, flashing costs, etc. Therefore, the actual installed price would typically be higher. Depending on the building, other factors such as size, complexity of the project, number and type of
penetrations, debris removal, etc can add to the cost of the roofing system. Roofing contractor’s prices can vary substantially depending on overhead, travel expenses, productivity, compliance with safety and health regulations, warranties fees, etc.
Additionally the “Estimator” contains modifiers for different cities to reflect differences in material and labor costs. For example, San Diego pays on average 18% more for labor than the
Table 2: Cost of SPF Roofing System Compared to Membrane System over 30 years adjusted to 2009 costs
(20,000 sq ft Roof)
Southern CA Cost of roof system over 30 years Initial Cost /sq. ft. Coating Cost /sq. ft. Tear-off Cost/sq ft 2 “ SPF w/10 year Re-coat R 12-14 $138,000 $3.85 $1.52 (x2) N/A 2” SPF w/15 Yr. Re-coat (R 12-14) 107,400 $3.85 $1.52 N/A 3 Ply BUR 10 year system (R 12-14 polyiso) 246,600 $3.23 (x3) N/A $1.32 (x2) 4 Ply BUR 15 year system (R 12-14 polyiso $180,800 $3.86 (x2) N/A $1.32
(N/A = not applicable)
As the table indicates, it is assumed the SPF roof would require one recoat at the 15 year mark. The 3-ply BUR would require a tear and replacement at the 10 and 20 year mark. The 4-ply BUR would require tear-off and replacement at the 15 year mark.
The following table contains cost estimates of membrane systems most commonly used in the western states. The reader can extrapolate the data to calculate life cycle costs for systems not provided in the article.
Table 3: Roofing System Cost per National Construction Estimator
Item Material Cost
(sq ft)
Labor Cost (sq ft)
Total (sq ft) With R 12-14 insulation
BUR 3-ply smooth 0.79 0.68 1.47 3.23
BUR 4-ply smooth 1.31 0.79 2.10 3.86
BUR 3-ply w/light aggregate BUR 4-ply w/light aggregate
0.79 1.31 0.68 0.79 1.97 2.60 3.73 4.36 BUR 3-ply w/heavy aggregate
BUR 4-ply w/heavy aggregate
0.79 1.31 0.68 0.79 2.27 2.90 4.03 4.46 Modified Bitumen 2.25 0.84 3.09 4.85
Roll Roofing (double coverage) 1.42 0.30 1.72 3.48
Polyiso Board insulation R 13 1.36 0.40 1.76 N/A
SPF w/acrylic coatings R 15 3.08 79 3.87 N/A
According to contractors surveyed in California and Arizona, the most common insulation used in roofing applications is polyiso board. The “National Estimator” installed cost of 2 inches is reported at approximately $1.76 per sq ft. Depending on the membrane roofing system used, the combined cost of a membrane roofing system plus R 12-14 of insulation would range from $3.23 on the low end (3 ply smooth surfaced BUR) to a high of $4.85 on the high end (modified
bitumen). A SPF roofing system that is rated at R 12-14 would have an installed cost of $3.87 per sq/ft. (Note: additional insulation would be required to provide slope as required to enhance system performance or to comply with local building codes.)
This data indicates that SPF roofing systems have become more affordable compared to
insulated membrane roofing systems between 2003 and 2009. Therefore, its life cycle cost would provide even greater benefit to the building owner.
Other Research on Life Cycle of SPF Roofing Systems
As can be observed from table 2, even with the energy benefit deducted, a SPF roofing system recoated every 15 years is still less costly to install and maintain than a very low cost membrane roofing system. But, is this a fair comparison? How often do SPF roofing systems require a re-coatIng? How long do they really last?
In 1997 and again in 2003, Dr Rene Dupuis of Structural Research Inc. was commissioned by the National Roofing Foundation to conduct research on SPF roofing systems in six different climate zones in the United States. Based on inspections and sampling of over 300 SPF roofing
systems, Dr. Dupuis concluded that SPF roofs have an effective service life of more than 30 years. The research also shows that the physical properties of the foam change very little with age. This indicates that the life expectancy of a SPF roof system depends primarily on the original application and long-term maintenance. In the first study, Dupuis reported the average service life of the SPF roofing systems before recoat was 11 years. In the subsequent study in 2003, the average recoat cycle had increased to 15 years. Based on the results of the 1997 study, Dr Dupuis reported “SPF Roofing Systems are one of the most sustainable systems to date.”
Depreciation vs. Maintenance
A common question by building owners concerns whether a SPF roofing system installed over an existing membrane roof is considered a new roof system (and therefore subject to long term depreciation as a capital improvement) or as a repair to the existing roof system (and therefore deductible as a maintenance/repair item).
Installing a SPF roofing system over an existing membrane system is considered a new roof by the roofing industry and building codes. As such, it is depreciated as any other new roofing system as a capital improvement.
But, looking down the road 10 to 15 years, a SPF roofing system can offer significant tax benefits over a membrane roofing system. As we discussed earlier, SPF roofing systems on average are recoated on a 15 year cycle. Most membrane roofing systems last 10 to 15 years before a replacement is required. Each time a membrane roofing system is replaced, the new roofing system is depreciated as a long term capital improvement.
In a 30 year life cycle, this difference can add up to thousands of dollars saved by the building owner.
Other Factors That Affect 30 Year Life Cycle Costs
Premium costs of landfill debris: According to the National Roofing Contractors 1999 annual survey, more than 68.5% of the 11.3 billion dollar low slope re-roofing market included tear-off and replacement of the existing roof membrane The state of California extracts a premium cost for disposing of asphaltic based materials in landfills. These costs are only going to get higher. Some membrane systems may require 2 tear-offs and replacement during the 30 year life cycle. The amount of debris from a 20,000 sq ft roof tear-off ranges between 10 to 20 cubic yards of material. Whereas a typical SPF roof application of the same size would yield less than 1 yard of debris, (mostly tape & plastic used to mask, HVAC equipment, windows, parapet walls, drains, edges, etc.) This extra cost of debris removal must be considered when determining the long term costs of a roofing system.
Providing slope for building code approval: The International Building Code and the state of California require new roofing systems to have a 1/4” per ft slope. On a flat roof deck assembly this may take as much as 10 inches of tapered insulation to achieve code approved drainage. Tapered insulation systems can raise the cost the new roofing system an additional $3 to $5 per foot. Every time a roofing system is removed and replaced, this added cost would be part of the 30 year life cycle/
However, when a new roof covering is installed over an existing roof membrane, building codes refer to this as a retrofit. The slope of the new membrane does not require the 1/4” per foot slope but rather provide positive drainage to eliminate ponds.
Consider that contrary to membrane roofing systems, over the 30 year life cycle the SPF roofing system does not require additional tear-off and therefore would not require a 1/4" slope. A SPF applicator can build crickets, dams and custom slope to existing roof decks so that positive drainage (i.e. no consequential water standing 48 hours after rain) can be achieved with
significantly less than a 1/4" slope. (Note: SPF roofing systems frequently exhibit small bird baths of water after rainfall. These are not considered ponds and are acceptable.)
Damage caused by roof leaks: As reported by Oakridge National Laboratories, (ORNL) in multiple workshops on low slope roofing, most deterioration in buildings comes from water or moisture issues. The majority of water damage comes from roof leaks. When membrane roofing systems wear out, the membrane tends to lose adhesion at the seams, flashing and around parapets walls and penetrations. Consequently, most membrane roofing systems will experience roof leaks in their life cycle before replacement. Maintenance agreements for membrane roofing systems frequently include leak repair costs that are not covered by warranties. Repairing roof leaks and the added cost associated with roof leaks (such as replacing mold remediation, replacing ceiling tiles, drywall, carpets, etc.) should be considered in the 30 year life cycle of the membrane systems.
Using the same inspection schedule, SPF roofing systems would average $350 per year. SPF has a very high impact absorbing quality. So while the foam surface can be damaged by impact from hail, wind driven debris, dropped tools, etc. this type of damage typically does not cause leaks. Furthermore, most damage can be repaired months later without compromising the long term performance of the roofing system. Most damage to the surface of the foam can be repaired with sealant at the time of inspection at no added cost to the owner
The following table takes a few of these factors into consideration.
Table 4: Cost of SPF Roofing System Compared to Membrane System over 30 years adjusted to 2009 (Other Cost Factors Added)
(20,000 sq ft Roof) Southern CA Cost of roof system over 30 years Initial Cost /sq. ft. Coating Cost /sq. ft. Tear-off Cost/sq ft Inspections Maintenance & Leak Repairs (avg cost/yr) Tapered Insulation to Provide Slope Landfill Costs 2 “ SPF w/10 year Re-coat R 12-14 $148,500 $3.85 $1.52 (x2) N/A $350/yr 2” SPF w/15 Yr. Re-coat (R 12-14) $117,900 $3.85 $1.52 N/A $350/yr 3 Ply BUR 10 year system (R 12-14 polyiso) $335,250 $3.23 (x3) N/A $1.32 (x2) $975/yr $3.00/ft (x2) ? 4 Ply BUR 15 year system (R 12-14 polyiso $269,250 $3.86 (x2) N/A $1.32 $975/yr $3.00/ft ?
Based on Michelson’s study, and updated material and labor costs, SPF roofing systems demonstrate a proven cost savings over a 30 year period over membrane roofing systems even without considering energy saving benefits.
So for the property manager or owner looking to save roofing and maintenance costs, take a second look at the SPF roofing systems. It can be worth it in the long-run.
Side Bar:
What is spray polyurethane foam roofing?
SPF has a closed-cell structure that makes it water resistant. It must, however, be protected by elastomeric coatings or other coverings (such as aggregate) to prevent ultraviolet-induced surface degradation. Such coverings can also be used for other purposes, including inhibiting moisture vapor transmission, enhancing the aesthetics of the system, increasing the impact and abrasion resistance of the system, and achieving flammability and code requirements.
What type of life should I expect from a SPF roof?
In 1996 and 2003, the National Roofing Foundation commissioned Dr. Rene Dupuis of Structural Research Inc. to conduct research on SPF roofing systems in six different climate zones in the United States. Based on surveys of over 300 SPF roofing systems, Dupuis concluded that SPF roofs have an effective service life of more than 30 years. The research also shows that the physical properties of the foam change very little with age. This indicates that the life expectancy of a SPF roof system depends primarily on the original application and long-term maintenance. Noting the renewability of the systems, low maintenance, resistance to roof leaks and reduction in construction debris, Dr Dupuis reported “SPF is one of the most sustainable roofing systems to date”.
Other studies such as Dr Dean Kashiwagi’s surveys of more than 2000 SPF roofing systems over a 15 year time frame confirm Dr Dupuis’ research. Dr. Kashiwagi’s 1996 survey reported; “the oldest performing SPF roofs are more than 26 years old, 97.6% did not leak, 93% had less than 1% deterioration, and 55% were never maintained”.
SPF roofing systems typically are recoated at regularly scheduled intervals to extend the life of the system. According to Dupuis’ research, SPF roofing systems currently average 15 years between recoating cycles.
Where is SPF used?
SPF roofing systems have good adhesion to a variety of substrates, including metal, wood, concrete, and built-up roofing (BUR). Since SPF adds little weight to existing roof coverings and can build slope to fill in low areas, these systems are used frequently as a recover roofing system. Caution should be used when specifying any recover roofing system. The existing roof covering and roof deck assembly should be thoroughly evaluated to verify that it can be a good substrate for SPF roofing systems.
Hail and wind-driven missiles (such as tree limbs, broken roof tile, metal flashing, etc.) can damage the SPF roofing system. However, this type of damage typically does not cause leaks and can be repaired later without compromising the long-term performance of the system. SPF roofing systems also excel when the following conditions exist:
• Additional insulation is required. • There are severe temperatures.
• The roof substrate has numerous penetrations. • The roof deck is an unusual configuration.
• The roof is in an area where high winds are likely to occur. • Lightweight materials are required.
• Slope must be added to provide positive drainage.
Other Benefits:
Exceptional Leak Resistance & Wind-Uplift Resistance: ORNL reported, “The principal causes of premature roof failure are moisture intrusion and lack of wind resistance. Moisture accumulation in roofing systems leads to dripping, accelerated failure of the insulation and membrane, roof structure deterioration, depreciation of assets, and poor thermal performance. Similarly, the loss of a roof during a major windstorm not only causes structural damage, but also exposes the building contents to the elements. The insurance industry identifies roofing as the primary contributor to disaster-related insured losses.” Membrane roofing systems leak if the membrane is punctured or if it separates at the seams, flashing, penetrations, etc.
SPF roofing systems limit moisture intrusion because of it’s 90% closed cell properties. Damage to the system typically does not cause leaks into the building, and moisture intrusion is isolated to the areas of damaged foam cells. As reported by Dr. Dupuis, “One unique aspect of SPF roofs… is that they are not in immediate danger of leaking, providing the penetration does not extend all the way through the foam.”
SPF roofing systems have marvelous wind up-lift resistance. Field observations of SPF performance during Hurricanes Allen, Hugo and Andrew led the industry to conduct laboratory testing of SPF systems at Underwriters Laboratories and Factory Mutual. SPF’s wind uplift resistance exceeded the capacity of UL’s equipment. UL also observed that SPF roofs applied over BUR and metal increased the wind uplift. Factory Mutual has given SPF roofing system installed over concrete decks an I-990 wind uplift resistance rating (the highest rating possible). Proven Sustainable Characteristics: At the 1996 Sustainable Low-Slope Roofing Seminar, Oak Ridge National Laboratories described sustainable or green roofing systems as “roofing systems that have a long life, low maintenance, save energy, add durability to buildings, control moisture in buildings, and contribute very little to the waste stream.”
Noting the renewability of the systems, low maintenance, resistance to roof leaks and reduction in construction debris, Dr Dupuis reported “SPF is one of the most sustainable roofing systems to date”.
Another researcher, Dr Dean Kashiwagi (a teaching professor at the Del Webb School of Engineering at Arizona State University) has been conducting surveys of thousands SPF roofing systems since the 1980s. His surveys continue to reinforce the sustainable characteristics of SPF roofing systems. For example, Dr. Kashiwagi’s 1996 survey reported; “the oldest performing SPF roofs are more than 26 years old, 97.6% did not leak, 93% had less than 1% deterioration, and 55% were never maintained”. He continues to find similar results on SPF roofing systems today.
Energy Savings:
Spray polyurethane foam can help to keep energy costs low because it is applied as a seamless layer above the roof deck, covering fasteners, gaps, cracks and other thermal bridges that rob membrane roofs of their insulation efficiency with a highly effective, high R value insulation. The insulation is applied above the roof deck making it more effective and is typically coated with light-colored, reflective coating, thereby reducing the overall temperature of the roof’s surface.
What about Costs?
SPF roofing systems vary widely in cost depending on the foam thickness required, the type and thickness of the coating or covering, the degree of substrate preparation, labor costs, regional pricing structures, complexity of the roof design, availability of contractors in a specific region, and other factors. As with other roofing systems, there are high-end and low-end SPF roofing
systems. On the high end are silicone and polyurethane coated SPF systems. On the low-end are acrylic coated SPF systems. The climate and environmental aspects of most regions in California and Arizona favor the use of acrylic coatings. Acrylic coatings are not only less
References:
• SPFA Life Cycle Cost Study of SPF Roofing Systems vs. Membrane Roofing Systems, Dr Theodore Michelsen, 2003
• A Field and Laboratory Assessment of Sprayed Polyurethane Foam-Based Roof Systems, Conducted for the National Roofing Foundation by Rene M. Dupuis, Ph.D. P.E., Structural Research, Inc Phase I, 1997; Phase II 2003.
• Proceeds of the Low Slope Workshop Oakridge National Laboratories, 1996-2000.
• Factory Mutual Research Report, Spray Polyurethane Foam Roofing with Protective Coating Systems in Class I Roof Deck Assemblies. 2005
• National Construction Estimator,Dave Ogershok & Richard Pray published by Craftsman Book Company, 2009
• 1996 Roofing Contractors/Systems Performance Information, Dean Kashiwagi Ph.D. P.E.,
• Sustainability Characteristics of SPF Roofing Systems, M. Knowles, Environmental Design and Construction, 2004
• Building Thermal Envelope Systems and Materials, UPDATE, April 1996, Envelope Research Center, Oak Ridge National Laboratory
• Energy Conservation and Thermal Envelope Design Using Polyurethanes, Spray Polyurethane Foam, Mason Knowles, SPFA, Presented at ACSA Construction Materials and Technology Institute, 1996,
• University of California at Berkeley, Berkeley, California
• Spray Polyurethane Foam Roof Insulation with Protective Coatings for Use in Recover Roof Construction and New Construction over Structural Concrete Roof Decks, Factory Mutual 4470 Test, 1996
• An Update on Hail and Wind Considerations, Richard L. Fricklas, SPFA Newsletter, May, 2000 • SPF Tomorrow’s Roof Today, SPFA Brochure, AY 129