How to evaluate SPF’s viability for your roof and ensure a successful installation
How to evaluate SPF's viability for your roof and ensure a successful installation.
Good building management requires sound decisions on a wide spectrum of subjects, not the least of which is the all-important roof – the Fifth Wall.
When the roof’s condition or lack of maintenance become issues, lack of adequate management reveals itself at the most inconvenient times, usually during a major thunderstorm or record blizzard. Not only must you then deal with water damage, but roofing companies will be swamped with similar calls for service and may not be able to get to your building for days or even weeks.
With semi-annual scheduled inspections and an up-to-date roofing file, it is possible to minimize the potential for roofing failure while also updating your estimate of the remaining roof life for replacement budgeting purposes.
Assume we have decided to replace the existing roof system with a sprayed in place polyurethane foam system. That decision process has included cost analysis, warranty information, and future needs for the building.
Roofing experts will then gather information on what is currently keeping the water out. They will first need to know how many roof systems are in place. Most building codes limit the building to two membrane systems, so if there are already two in place, at least one must be removed. (When the number of roofing membranes are counted, it is important to note that building codes do not count coatings as separate membranes.) When re-roofing or re-covering, the building must be upgraded to meet the current roofing code.
Compliance items will include:
- Scope of wet insulation. No code permits placing a new roof system over wet insulation or a rotted deck. (In some parts of the Southwest, loose-fill volcanic pumice was once an acceptable insulation, but the codes no longer allow it. When this kind of insulation is encountered, regardless of any other condition, the roof over it and the pumice must be removed before a new roof can be installed.)
- Slope of new system. Some codes now permit “positive drainage,” while others may call for a minimum of 0.25-inch slope (2%) per foot. Tapered insulation ensures good slope to drain. Using crickets and saddles will also help direct the water to a drain or scupper.
- Amount of thermal insulation. Prior to the oil embargo of 1972-1973, typical roof insulation thickness would have been 0.75 inches with an R value of 2.75 to 3. With all the focus on energy conservation today, minimum R-values are more likely to be 10 times that, around R=30. Even with more efficient thermal insulations, that increase in R-value presents in a substantial increase in the thickness of the roof system, which in turn will require elevating roof edges and curbs at significant cost. At a certain point, costs rise faster than energy is conserved, a principle known as the law of diminishing returns. In addition, published R-values should be based upon long term thermal resistance (LTTR).
- Eligibility for a new roof warranty. Most membrane manufacturers will require all existing roof systems be removed down to the deck, and that thicker membranes (i.e., at least 90 mil instead of 45 mil) be employed where there will be significant roof traffic or where severe hail might occur.
What to Consider During an SPF Installation
When installing spray foam insulation, proper surface preparation is vital. For existing gravel-surfaced built-up roofing, use a high-pressure, low-volume wet-vac to remove loose surfacing and dirt. A clean substrate is a must.
Next, determine the attachment of the old roof. If it’s suspect or inconsistent, you can mechanically attach the existing roof system before spraying down the new SPF. Also make sure to stick to the SPF system provider’s instructions for use, including using a primer and choosing a recommended coating, such as acrylic, silicone, or urethane elastomer.
The system also needs adequate compressive strength to resist foot traffic and hail impact – the recommended density is at least 2.75 pounds per cubic foot. A wind shield used with a robotic SPF application will minimize overspray. Most importantly, the roofing contractor must be accredited by the Spray Polyurethane Foam Alliance (SPFA).
SPFA offers a wealth of information on proper spray foam application, as does the National Roofing Contractors Association (NRCA), RCI Inc., and the standardization body ASTM. Look into some of these documents to beef up your SPF knowledge:
SPFA: AY-102 Guide to Selection of Coatings, AY-104 SPF Systems for New and Remedial Roofing, AY 107 SPF Blisters, AY-137 Equipment Guidelines, AY 139 Repair of SPF Hail and Wind-driven Damage, SPF Live Cycle Cost Study (Michelsen Technologies)
NRCA: Field and Laboratory Assessment of SPF Roof Systems (4th International Symposium on Roofing Technology -1997), NRCA Manual on SPF Systems, NRCA SPF Roof Systems
ASTM standards: C1029 Specification for SPF Thermal Insulation, D5469 Guide Application of New SPF, D6083 Acrylic Coatings, D6694 Silicone Coatings, D6705 Repair and Recoat, D6947 Liquid-Applied Moisture Cured Polyurethane Coating, D7119 Sampling SPF and Coating, D7425 Standard Specification for SPF Used for Roofing Applications
RCI: Field Performance of SPF Foam Flashings by Rene DuPuis, 2004; Sustainability Characteristics of SPF Roofing and Insulation Systems by Mason Knowles, 2004
Other useful resources: Maintenance and Repair of SPF Roofing by the U.S. Department of the Interior, 1994; sprayfoam.com
Richard (Dick) L. Fricklas was technical director emeritus of the Roofing Industry Educational Institute prior to his retirement. He is co-author of The Manual of Low Slope Roofing Systems and continues to participate in seminars for the University of Wisconsin and RCI Inc., the Institute of Roofing, Waterproofing, and Building Envelope Professionals. His honors include the William C. Cullen Award and Walter C. Voss Award from ASTM, the J. A. Piper Award from NRCA, the William C. Correll award from RCI, and the James Q. McCawley Award from the MRCA. Dick holds honorary memberships in both ASTM and RCI Inc.
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