Functions of low-rise foam

By now, you most likely have been involved with or are aware of a roofing project or specification that required the use of low-rise polyurethane foam adhesive. Because the frequency of projects using low-rise foam adhesive has increased in recent years, it is critical you understand the product's benefits and drawbacks and opportunities for its use. Doing so will enable you to locate projects where using the product may be appropriate.

Although low-rise foam has its drawbacks, most of which are related to application and equipment costs, there are advantages to using it to install roof assemblies. My roofing company, Jurin Roofing Services Inc., Quakertown, Pa., has realized numerous benefits from using the product. We have used it to drive the development of our Commercial Roofing Division, which, during 2001, installed more than 500,000 square feet (45000 m²) of roof systems incorporating foam adhesive. The product is best explained in the context of projects we have completed during the past several years. (Factory Mutual Research criteria did not apply to these projects.)

Attachment to non-nailable substrates

Often, building owners ask roofing contractors to provide pricing for roofing projects that require creativity in roof system design. On many occasions, contractors are presented with deck types that limit attachment options. The use of low-rise foam adhesive offers an alternative to traditional fastening methods, such as the use of mechanical fasteners or hot asphalt. For example, using foam adhesive enabled us to complete a 50,000-square-foot (4500-m²) Carlisle Fleeceback installation for a major Northeast real estate investment trust company.

The building, located in Long Island, N.Y., houses a repair center for a major camera equipment manufacturer. The roof deck was a fiberglass form board with lightweight gypsum poured over the form board. The building already had been reroofed once, so the option of reroofing again was not available to the owner. A tear-off was required, which meant the deck could suffer some fracturing during the removal of the existing roof systems because the intermediate layer of recovery board was mechanically attached to the roof deck. With the removal of two roof systems and insufficient pull-out values offered by the deck, the use of mechanical fasteners was not an option.

The use of low-rise foam adhesive allowed us to design a roof system that incorporated the application of an EPDM membrane directly over the gypsum deck. The membrane was adhered to the surface of the gypsum with a continuous application of foam adhesive. The membrane's adherence directly to the gypsum surface eliminated dependence on mechanically fastening any portion of the roof assembly.

Low-rise foam adhesive permits the direct application of membrane and insulation board to most substrates. This creates a viable alternative to mechanically fastening and using hot asphalt for the adherence of membrane and insulation.

A concern for contractors who use low-rise urethane foam to attach a product to a deck substrate is the surface temperature of the roof deck on which a membrane is being installed. When installing foam adhesive, you must achieve a reaction between the two parts of the foam adhesive that results in the foam rising. Once the foam rises, you can set a product, such as an insulation board or membrane, into the foam. But the reaction that results in the rise requires heat. If a deck is below the temperature required by the adhesive manufacturer, the chemical reaction is inhibited. This affects the development of the closed cell and proper foam formation.

Improper formation increases the potential of premature roof failure and roof system blow-offs. This problem becomes more evident in colder climates or on projects where temperature-sensitive environments are located directly beneath a deck. You should consult the requirements of the adhesive manufacturer before applying a product. Manufacturers may require the addition of a catalyst to the foam mixture to activate the reaction in cases of insufficient temperatures.

Underside obstructions

Almost every commercial roofing contractor has had to contend with obstructions that were mounted to a roof deck's underside. Such obstructions may include electrical or telecommunications conduits; duct work; conveyance systems; and other mechanical, electrical or plumbing systems that are contained within a building. The presence of obstructions can inhibit mechanically attaching a roof system.

For a recent project for a national retail chain, one of our roofing crews encountered conduits that were used to power the building's emergency lighting system. The project originally was designed to have a polyisocyanurate insulation board mechanically attached to a metal roof deck.

Because the presence and location of the conduits were not disclosed at the project's start, on the first day at the job site, the roofing crew penetrated a conduit with a mechanical fastener and, consequently, shut down the building's emergency lighting system. After further exploration above the drop ceiling by Jurin Roofing Services and the building's facility management personnel, it was noted by the project manager that the conduits were present throughout the roof deck's underside. Additional mechanical attachment of the insulation could have resulted in more damage to the building's electrical system.

Because an EPDM system had been selected, we already were in the process of using foam adhesive to install the roof system. We were able to make the transition to setting the insulation board into low-rise foam adhesive onto the metal deck and eliminating the potential of puncturing the remaining conduits.

The project was finished without further incident or disruption to the building's operation.

Freezer applications

The design and application of roof systems over freezer buildings often is debatable because of issues such as the location of the dew point, thermal bridging and moisture drive. When designing roof systems for freezer buildings, roof system designers must consider criteria that do not affect the design and application of roof systems on typical structures. For example, designers must be concerned with vapor retarder placement, moisture intrusion through the system, R-value, dew point and interior humidity levels.

We were asked by a national meat-processing company to address a problem at its main processing facility. The problem occurred when the exterior temperature would drop below the interior temperature—condensation would form on the roof deck's underside and freeze. This frozen condensation created spalling on the roof deck's underside.

The condensation was evident in a holding room for freshly killed animals that were being readied for processing. The company had been experiencing this problem since the building's construction more than 15 years ago. The condensation was the result of air leakage caused by a lack of vapor retarders being incorporated into the roof system. The roof system was a ballasted EPDM membrane installed over 5 inches (127 mm) of polyisocyanurate insulation board set directly onto the concrete planks that created the room's ceiling. The room was chilled to 28 F (-2 C), but as the room chilled, it was used for washing the meat before it moved to processing. This resulted in high relative humidity levels.

In most cases, vapor retarders need to be placed on the warm side of a roof assembly because warm, moist air will move toward cooler, drier air. In this particular case, the warm side of the roof system changed according to whether the facility's interior was warmer or cooler than its exterior. As a result of these conditions, two vapor retarders were used to ensure moisture intrusion would not affect the roof assembly at either temperature extreme.

Using mechanical fasteners to install a roof system could compromise a vapor retarder if mechanical fasteners are permitted to penetrate the vapor retarder. In the case of this project, a vapor retarder was used to reduce the possibility of condensation on the deck's underside by limiting the movement of the interior moisture toward the building's exterior in cooler temperatures.

To solve our client's problems, we installed a self-adhering waterproofing membrane onto the deck and set a double layer of 2 1/2-inch- (635-mm-) thick polyisocyanurate insulation onto the vapor retarder in a continuous application of low-rise foam adhesive. Afterward, a TPO roof membrane was fully adhered to the insulation's surface, completing the roof assembly. The entire roof assembly received a 20-year warranty from the manufacturer.

By using foam adhesive rather than mechanical fasteners, we ensured against screw degradation as the result of thermal bridging. Also, by eliminating mechanical fasteners, the installation contributed to energy savings for the building owner.

However, the success of the roof system installation was, in part, based on the use of a vapor retarder installed before the foam adhesive. Low-rise urethane foam does not have an acceptable perm rate that would allow it to act as a vapor retarder for a roof assembly. Therefore, low-rise urethane foam should not be used as a vapor retarder for roof assemblies.

Aesthetic appearance

In an effort to design buildings with a more modern appearance, architects and designers are using decks' undersides to create a desired effect. As a result of this trend, penetrating a deck's underside with mechanical fasteners is discouraged. Using asphalt is ruled out in some cases because of the possibility of hot bitumen dripping inside a building through openings in a roof deck during installation.

We encountered such a roof deck in the replacement of a gravel built-up roof (BUR) system on a shopping mall north of Pittsburgh. The roofing project involved retrofitting the roof system, which was installed over a metal deck. A portion of the metal deck was exposed on the interior above a portion of the showroom floor, which had been designed to appear more modern than other areas of the store. Mechanically fastening the insulation board would have left the fastener tips exposed to the building's interior, as well as damaged recently applied paint.

The replacement system for this roof assembly was a fully adhered EPDM roof system installed over a 1-inch- (25-mm-) thick polyisocyanurate insulation board. The new insulation board was attached to the existing roof surface using low-rise polyurethane foam adhesive. Before installing the foam, the gravel surface was swept using a pneumatic vacuum to remove excess gravel. Doing so ensured we were attaching foam and insulation to a stable, secure surface. This allowed a new roof system to be installed on the building's top surface without compromising the original interior aesthetic effect intended.

Using foam to adhere an insulation board to a substrate is a useful tool for roofing contractors. The surface to which insulation or a recovery board is being adhered affects the foam adhesive's application rate. Roof systems and decks that exhibit uneven surfaces, such as gravel-surfaced roof systems or metal decks, invariably will require more foam to complete attachment than will a smooth-surfaced BUR membrane or concrete roof deck. Beware of application rates during bidding processes to avoid costly shortages of material on job sites.

Installation window

Traditional, fully adhered EPDM roof systems are prone to wrinkling and distortion during the installation process. This is a result of using solvent-based adhesives that must flash off before attaching a membrane to its intended substrate. More times than not, wrinkles or distortions in a sheet are the result of conditions beyond the control of an installation crew. Certain weather conditions, such as wind, can wreak havoc during roof membrane installation, creating massive wrinkles in a sheet.

Although wrinkles are not of concern to most manufacturers unless they intersect a field seam, they do minimize the aesthetics of a roof system and may cause concern to a client.

Low-rise polyurethane foam adhesive allows for a much greater window of time in bonding sheet goods or insulation to an intended substrate. The difference in the technology is that foam adhesive is not required to flash off before mating two surfaces.

For instance, let's say a heavy wind gust develops during the mating of an EPDM membrane to an insulation board using low-rise urethane foam adhesive. The wind causes a roofing worker to set the sheet incorrectly, which leaves a wrinkle in the sheet that intersects a field sheet. Traditionally adhered roof systems would require the worker to move on to the next sheet and return to cut out the wrinkle and apply a field patch to the location. If the same situation were to occur with the use of low-rise foam adhesive, the sheet may be lifted and reset before the adhesive has bonded the membrane to the substrate. There is a greater window of opportunity to maneuver the sheet before the adhesive sets.

Overview

The use of low-rise polyurethane foam adhesive in roof assemblies includes many benefits beyond those that have been given. Other qualities inherent to the use of the foam adhesive are increased wind-uplift ratings; speed of installation; and minimization of the use of solvent-based materials in roof assemblies. But note that the material has certain application requirements that can be difficult to achieve; application equipment is a significant investment; and workers must be trained appropriately. Because foam adhesive is relatively new, those who use it are continuing to learn of its shortcomings on a job-by-job basis.

The use of new technologies in the application of roof systems is critical to the roofing industry's future. I believe the use of products such as low-rise foam, which minimizes a contractor's dependence on an unstable labor force, will bolster contractors' abilities to provide quality roof system installations at fair prices. As industry professionals, we must continue to explore options that will assist the roofing industry in its ongoing evolution.

Chris Jurin is vice president of Jurin Roofing Services Inc., Quakertown, Pa.