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SPF Roof Systems

By Ed Lundin

Following are some proven facts to help dispel some of the misconceptions about polyurethane foam roofing systems

Spray-applied polyurethane foam, which has been used as a roofing system since the 1960s, is being applied successfully throughout the world. Traditionally used as a reroofing system, it is now being used in the new construction market, as well.

As the industry has evolved and matured, many misconceptions about sprayed polyurethane foam also have evolved. Most of these myths are based on misinformation held by individuals who are not familiar with the system. As with all myths, the, have been repeated so many times, that it has been hard to separate fact from fiction.

The purpose of this article is to separate fact from fiction, and to point out some of the misconceptions about this roofing system.

A reliable system

Myth: Sprayed polyurethane foam is all experimental roofing system and has not yet been proven in the field.

Fact. Spray-applied polyurethane foam has proven over the years to be a viable roofing system. The application of sprayed polyurethane foam has become technically based, with established parameters for successful application. These parameters are often similar to those that are necessary for the successful application of a built-up or single-ply roof.

Myth: Sprayed Polyurethane foam is not a long-lasting roofing system.

Fact. Similar to other successful roofing systems, a sprayed polyurethane foam roof can last more than 20 years when properly specified, applied by skilled applicators and maintained.

Mechanical damage is usually easy to repair on a polyurethane foam roof with a sealant and a caulking gun.

There are millions of square feet of successful polyurethane foam roofs that are more than 20 years old. The one thing that they have in common with each other and with other successful systems is that they were installed by conscientious, well-trained roofing contractors.

Myth: Sprayed polyurethane foam is soft and cannot be walked on.

Fact: Specifications formulated by the Society of the Plastics Industry's Polyurethane Foam Contracting Division (SPI/PFCD) require that polyurethane foam used in roofing applications have a density in the range of 2.8 to 3.0 pounds per cubic foot. This results in a compressive strength of 40 pounds or more per square inch, which is greater than that of other plastic foam board insulations that are commonly used in other types of roof systems.

According to SPI/PFCD, maintaining these prescribed physical properties will prevent mechanical damage to the surface of the insulation and coating system under normal roof traffic conditions.

If severe or unusual traffic conditions are anticipated, the use of a walkway across the polyurethane foam roof is recommended. As with other systems, there are recommended ways to construct or install a walkway, and the material manufacturer should be consulted.

Unlike some other systems, however, mechanical damage on a polyurethane foam roof is easily recognized and usually can be repaired at minimal cost to the building owner. In addition, puncture of a polyurethane foam roof does not typically result in leakage; though the coating may be punctured, the foam itself is able to resist water for a considerable time.

Myth: Birds eat polyurethane foam.

Fact: Birds do not eat polyurethane foam, though they will sometimes peck at the foam until they break through the coating. The problem should be treated no differently than any other mechanical damage. Regular inspections, with a caulking gun in hand, can quickly repair this type of damage.

The use of more durable coatings, granules or a combination of both is recommended to help alleviate the problem. Some coating manufacturers have "bird proof" warranties, and their specific recommendations should be followed.

Adverse weather

Myth: Sprayed polyurethanefoam cannot be used in my area because harsh weather conditions sometimes exist.

Fact: Sprayed polyurethane foam has been successfully applied in most areas of the world, as well as in all 50 states. Weather conditions necessary for the application of polyurethane foam are similar to those required for most other roofing systems. The three weather extremes about which all roofing contractors must be aware are temperature, humidity and wind.

Temperature extremes

Most polyurethane foam manufacturers recommend application temperatures between 45 and 120 degrees, which is similar to the temperature range in which built-up roofing (BUR) and most single-ply roofing systems are normally applied. However, roofing contractors should be aware that they need to account for not only one, but two, temperatures-ambient and surface.

Low ambient temperatures can prevent polyurethane foam from being properly applied. If the stored chemical is too cold, it cannot be properly heated by the equipment. Heated storage areas and drum heaters can help alleviate problems associated with low ambient temperatures.

High ambient temperatures, on the other hand, typically do not present a problem, because the chemical is heated by the equipment to a temperature range of 130 to 140 F. This is above ambient temperatures at most jobsites.

Surface temperatures are more critical to the application of polyurethane foam roofing systems, and must be monitored accordingly.

Polyurethane foam uses a chemical reaction called exotherm (heat). This heat is self-generated. If the foam is sprayed onto a surface that is too cold, the surface will act as a "heat sink," preventing proper chemical reaction.

Conversely, extremely hot surface temperatures will have the opposite effect. The foam may overreact, again resulting in a finished product with poor physical properties.

Most manufacturers formulate their polyurethane foam in three grades-winter, summer and spring/fall. Each manufacturer has its own temperature range for these standard formulations, and can adjust the ranges (by adjusting the formulations) if requested.

Using dark-colored primers in cold weather and white or light colored primers in hot weather can also help contractors to achieve a quality application.

Humidity

Polyurethane foam manufacturers require that foam not be applied to the roof if the temperature is within 5 degrees of the dew point. No roofing system should be applied at (or past) the dew point, because moisture will be present.

Calculating the dew point is not as easy as getting the outside temperature. It must be determined at the jobsite and, in some areas and under some conditions, it should be checked hourly.

For example, on a sunny day, it is unlikely that a small fluctuation in the dew point will present a problem, but on a cloudy day, or in the early morning or late afternoon, contractors should monitor the dew point regularly. High relative humidity can affect the "in place" density of the polyurethane foam, and in a given situation where high relative humidity exists, the manufacturer's recommendation must be followed.

In the humid South, there are situations when the relative humidity is above manufacturers' recommendations during some part of the working day. However, there are also plenty of sunny days with relative humidities of 60 and 70 percent, which is below manufacturers' limits. Suffice it to say, there are millions of square feet of successful polyurethane foam roof applications in cities such as San Antonio, Houston, New Orleans and Mobile, Ala.

To determine the dew point and relative humidity, many contractors use a psychrometer. This instrument, which is widely used in the painting industry, is available from most industrial supply houses. Used with a psychrometric chart, it is easy to perform testing on the jobsite in a matter of minutes.

Wind considerations

High wind speeds can cause problems for all roofing contractors, regardless of which system is being installed. Contractors must be aware of wind-chill and application temperatures, materials blowing around on the roof and materials blowing, onto finished surfaces that will later have to be cleaned. This type of "over-spray" can cause property damage and rough foam, because uncured materials are being deposited onto completed surfaces of the roof. Robotic spraying machines or wind shields can allow for successful application in winds as high as 25 mph

To sum up the weather parameters, polyurethane foam should not be applied when the ambient temperature is within 5 degrees of the dewpoint, or when the relative humidity is above the manufacturer's recommendation. Extremes in temperature and wind velocity may create problems that to some extent can be compensated for, but the contractor must know the capabilities of his equipment, materials and crew.

It should be noted that these weather-related problems are not unique to the polyurethane foam industry. All roofing contractors must work within the parameters that have been set by the material manufacturers and follow good, proven roofing practices. Making a blanket statement that weather conditions in a particular area are too severe for proper application of a specific roofing system is usually wrong.

Environmental viewpoint

Myth: Sprayed Polyurethane foam is not environmentally friendly.

Fact: In the past, chlorofluorocarbons (CFCs) were used as a blowing agent to give polyurethane foam its high insulation value. The CFC compound, which was used by most polyurethane foam manufacturers, reportedly had an Ozone Depletion Potential (ODP) of "1."

To be in accordance with the Montreal Protocol, which mandates the elimination of all CFCs by Dec. 31, 1995, the polyurethane foam industry has had to switch to an alternative blowing agent-hydrochlorofluorocarbons (HCFCs).

According to recent industry research, HCFCs, which are now being used by most polyurethane foam manufacturers, reduce the ODP by between 85 percent and 90 percent. In addition, other government regulations have spurred research by many foam manufacturers that may eventually bring the ODP in polyurethane foam down to 0.

Polyurethane foam is also environmentally friendly in other ways. The product, either sprayed-in-place or board stock, contains recycled resins, such as polyethylene terephthalate (PET).

In addition, because polyurethane foam insulation has a high R-value, and because there are no insulation fasteners or board joints to create thermal bridges, sprayed-in-place polyurethane foam roofs can help to reduce the amount of fossil fuel required to heat and cool a building.

Maintenance concerns

Myth: Sprayed polyurethane foam systems require too much maintenance.

Fact: All roofing systems should be inspected annually, so that minor problems do not become major ones. Sprayed polyurethane foam is no exception to this rule.

Mechanical damage and most other problems are easy to identify and repair on a sprayed polyurethane foam roof, and can usually be repaired with a sealant and a caulking gun.

There is a tendency for those who are not experienced with this type of system to recommend removal of a polyurethane foam roof that has a few blisters and some mechanical damage. However, this roof can usually be repaired in three to four hours with an experienced crew; or, for an isolated puncture, the roof can often be repaired in a couple of minutes.

Depending upon the type and amount of coating that was used in the original application, the roof may have to be re-coated in the future. The roof should be re-coated when the top coat is worn to the extent that the base coat is exposed to the elements. However, there are many 20-year-old polyurethane roofs that do not yet need re-coating.

There are some inherent advantages to re-coating, which usually involves pressure-washing the roof and applying a new top coat. For example, some coating manufacturers offer new warranties for a re-coating job, giving the building owner the benefit of a "new roof" at very little cost. Timely re-coating will also save the owner the cost of labor and materials that would otherwise be required to install new foam and a new base coat.

Quality contractors

Myth: Qualfied Polyurethane foam contractors are very hard to find.

Fact: There are nearly 600 roofing contractors nationwide who are qualified to spray polyurethane foam roofs. More than 250 of these belong to SPI/PFCD, and as many as 50 of them are members of NRCA.

The names of these qualified roofing contractors can be obtained from SPI/PFCD or NRCA headquarters. There are also some 25 associate members that manufacture and specify sprayed polyurethane foam.

In 1987, recognizing the need to promote "professional roofing contractors," SPI/PFCD instituted an Accreditation Program. More than 200 roofing contractors and suppliers across the United States are now working toward achieving accreditation.

In the mid-1980s, NRCA established a Polyurethane Foam Roofing Committee. Among other things, the committee is currently striving to complete a polyurethane foam roofing section for NRCA's Roofing and Waterproofing Manual.

Wrapping it up

Over the years, there have been many misconceptions about polyurethane foam roofing systems. In part, this was due to problem jobs in the early days of polyurethane foam roofing, when application equipment was primitive, when foam densities were too low and when many applicators lacked adequate knowledge of polyurethane foam roofing principles.

The purpose of the above article is to dispel many of these "myths" with proven fact. The application of sprayed polyurethane foam has become an applied science, with state-of-the-art application equipment and established design and application parameters for successful roofing.

Similar to other roofing systems, a polyurethane foam roof can last more than 20 years when properly specified, applied and maintained by professional roofing contractors.

Ed Lundin, president of Lundin Roofing Co., Baton Rouge, La., is an NRCA director and a member of the Management Committee with SPI/PFCD. Jim Anderson, with Foam Enterprises Inc., contributed technical information for this article.

Professional Roofing - February 1993

Article Picture Gallery
A sample taken at a cut through the coating and polyurethane foam. The cut is about 1/4 inch deep. Foam damage was limited to the immediate area along the cut. The foam within a short distance from the cut was dry.	A robotic sprayer is being used to apply the coating. As the second coat is applied, surfacing granules are broadcast into the fresh coating by the worker on the left.	A robotic sprayer is being used to apply polyurethane foam.
The small, dark area near the end of the pen is a hole in the coating and foam. This is located in a small pond of clear water. Because of the foam's resistance to water penetration, leakage has not been reported.	Numerous piping penetrations along this wall were sealed relatively easy with the self-flashing foam and coating system.	General view of a very large manufacturing facility, which has several penetrations. This silicone-coated foam job was about four years old.