How would you roof these buildings?

NRCA member roofing contractors reveal how they would roof two fictional buildings in different climates

Energy-efficient roof systems are becoming increasingly present in the roofing industry. And there are various energy-efficient roof system options available. The approach to environmentally friendly roof projects could differ depending on the roofing contractor involved.

Professional Roofing presented NRCA member roofing contractors with parameters for two identical fictional buildings—one in a warm climate and one in a cold climate. The contractors were asked to choose how they would roof the buildings in an energy-efficient way and explain their decisions.

Following are the characteristics of the fictional buildings:

  • There are two identical buildings—one is located in a climate where cooling degree days (CDD) exceed heating degree days (HDD) by 2 to 1; the second is in a climate where HDDs exceed CDDs by 2 to 1.
  • The complex is a pharmaceutical company on a large tract of open land.
  • Energy and environmental issues are a high priority. Leadership in Energy and Environmental Design™ (LEED) points are critical to achieve an overall building complex ultimate goal of Platinum-level certification.
  • The entry/reception area is a 1 1/2-story vaulted steep-slope steel deck with the bottom side of the deck exposed and 48-inch overhangs. The exterior walls are glass.
  • A four-story attached office area has a steel deck and 36-inch perimeter parapet walls.
  • A two-story laboratory area has a concrete deck and multiple penetrations and is located so the prevailing winds blow away from the lab area.
  • A three-story material and product storage, on-site fitness and recreation space has a concrete deck designed to support a green roof system.

The following contractors contributed to the article: Casey Bechtel, president of H.J. Becker Co. Inc., Dayton, Ohio; Todd Kaska, vice president and regional manager of D.C. Taylor Co., Cedar Rapids, Iowa; Charles Schulz, project manager for F.J.A. Christiansen Roofing Co. Inc., Milwaukee; and Kent Tolley, vice president of Quality Tile Roofing Inc., Boise, Idaho.

Casey Bechtel

With regard to the entry/reception areas of both buildings, I would adhere two layers of 2-inch-thick polyisocyanurate insulation to the cleaned metal deck using a dual-component adhesive. This would keep the bottom side of the exposed metal deck free from any fasteners for aesthetics and thermal transfer. Then, I would completely adhere a colored PVC membrane roof system, heat welding extruded PVC ribs into place to simulate a standing-seam metal roof. On the cold-climate building, I would choose a dark-colored membrane. On the warm-climate building, I would choose a light-colored membrane.

On the four-story office area, I again would install two layers of 2-inch-thick polyisocyanurate insulation over the metal deck with a dual-component adhesive on both buildings. Then, I would adhere a black EPDM roof system on the cold-climate building and a white EPDM roof system on the warm-climate building.

When installing a roof system on the laboratory area with a concrete deck, I would choose a modified asphalt built-up roof system for both buildings for durability purposes because I always assume a roof with multiple penetrations will have a lot of foot traffic from service personnel. I would adhere two layers of 2-inch-thick polyisocyanurate insulation in hot asphalt. Then, I would adhere a layer of 1/2-inch-thick wood-fiber cover board in hot asphalt. I would install two plies of Type IV fiberglass felts in hot asphalt followed by a granulated modified cap sheet in hot asphalt. I also would install a white cap sheet on the warm-climate building and dark cap sheet on the cold-climate building.

With regard to the storage, fitness and recreation area, I would install a hot-melt liquid-applied rubberized membrane waterproofing system over the primed concrete deck with a green roof system that includes plants, walkways and benches. I would install this system on both buildings.

Todd Kaska

My recommendations for new roof systems on these facilities would be similar for both locations. The roof membrane system I recommend works equally well in hot and cold climates. The one difference between the two locations would be the amount of insulation with a higher R-value installed on the roof. The building in the colder climate likely would receive additional insulation or insulation with increased R-value. I would develop the overall scope of work with the owner or owner's representative to incorporate insulation levels that exceed American Society of Heating, Refrigerating & Air Conditioning Contractors Engineers (ASHRAE) requirements to contribute to the goal of Platinum-level LEED certification.

The first step when preparing to install a roof system on this facility would be to meet with the owner's representative to perform a job hazard analysis and develop a project delivery plan. A job hazard analysis identifies safety risks, countermeasures and an action plan to ensure a safe job site for all employees. The project delivery plan identifies owner objectives and values to be communicated to all field and management personnel. This preplanning is vital to ensuring the owner's objectives and values ultimately are met.

Experience with pharmaceutical facilities leads me to assume chemicals and hazardous materials may be emitted from penetrations on the lab area. A highly chemical-resistant roof covering is appropriate. In addition, because of the potential for above-average foot traffic, including the roof being used as a work surface, a highly durable roof system on those portions of the facility will be important for long-term performance.

Because the underside of the steel deck is exposed on the entry/reception area, I would recommend a fully adhered roof system. I would prepare the steel deck by pressure washing to remove any foreign materials or oils. I then would fully adhere two layers of 2-inch-thick polyisocyanurate insulation and a top layer of 1/4-inch-thick preprimed, gypsum-based insulation with low-rise foam adhesive. This would eliminate fasteners from being exposed on the underside of the steel deck. I then would fully adhere a 60-mil-thick PVC fleeceback membrane system with superimposed extruded PVC ribs hot-air welded to the roof membrane to emulate a standing-seam metal roof. The owner would be able to choose from a number of standard membranes and rib colors from the manufacturer.

On the four-story office area, I would install a 60-mil-thick white mechanically fastened roof membrane system. The membrane would be attached over two layers of 2-inch-thick polyisocyanurate insulation and a top layer of 1/2-inch-thick fiberglass-faced gypsum board. All three layers would be fastened to the steel deck with a common fastener. Walkway pads would be installed at roof access locations and around heating, ventilating and air conditioning (HVAC) equipment.

On the two-story laboratory area, I initially would prime the concrete deck with an asphalt primer and fully adhere a smooth modified bitumen self-adhering base ply. Penetrations and walls would be flashed with self-adhering modified bitumen base ply. The entire roof area would be prepared with the base ply before installation of the new roof system.

After the "temporary" roof membrane is installed, I would fully adhere two layers of 2-inch-thick polyisocyanurate insulation and a top layer of 5/8-inch-thick preprimed, gypsum-based insulation with a low-rise foam adhesive. A 72-mil-thick fleeceback white roof membrane system then would be fully adhered to the insulation. The 72-mil-thick membrane with the fleece-backing laminate provides a highly durable surface when applied over the insulation. Walk pads will be installed at roof access locations and around HVAC equipment.

On the three-story roof area, I would install an intensive green roof system. The system begins with PVC membrane strips fully adhered to the concrete deck to form a grid pattern. Then, a waterproofing membrane is loosely laid over a leveling layer and hot-air welded to the PVC strips previously adhered to the concrete deck. An additional felt separation layer, protection layer, drainage layer and extruded polystyrene insulation are loosely laid over the PVC membrane. The waterproofing system allows for subsequent installation of 12 inches or more of growth medium. This allows for a wide variety of vegetation and accessory green roof options from which the owner can choose.

Charles Schulz

I assume the buildings described have adequate slope to drains and do not need tapered insulation systems. I also assume building designs will accommodate the systems proposed. Furthermore, the insulation thickness used would be calculated to exceed ASHRAE 90.1, "Energy Standard for Buildings Except Low-Rise Residential Buildings," by no less than 50 percent to obtain tax credits from the government. Calculations would be accomplished with the assistance of NRCA's EnergyWise Roof Calculator.

I realize the cost of the proposed systems may exceed that of a system designed with value engineering and initial cost in mind. However, the life-cycle cost of the roof and goal for energy savings justify the front-end expense of the roof systems described.

I have a longstanding philosophy of using proven, time-tested roof assemblies and products. At the same time, I strive to stay on top of the marketplace by using new technology that has proved to be durable and cost-effective.

In the entry area, I would begin by mechanically fastening polyisocyanurate insulation with adhered plywood (nailbase) to the steel deck (in the warm climate, I first would install a 1/2-inch-thick thermal barrier). Over the nailbase insulation, I would install a self-adhering vapor retarder. The assembly would be completed by installing a custom-fabricated 24-gauge prefinished galvanized steel standing-seam metal roof and integral photovoltaic cells designed to offset the building's energy consumption.

With regard to the four-story attached office area in the warmer climate, I would mechanically fasten a 1/2-inch-thick thermal barrier to the metal deck with corrosion-resistant screws and plates according to the manufacturer's recommendations for the designed wind-uplift requirements. A two-ply vapor retarder then would be installed to the thermal barrier. In both climate regions, the system then would incorporate two staggered layers of rigid insulation installed with dual-component polyurethane low-rise foam. Over the insulation, I would install a 1/4-inch-thick preprimed gypsum cover board. The cover board also would be set in the same type of low-rise foam adhesive as described previously. I then would fully adhere a 50-mil-thick TPO membrane with a highly reflective white finish. Flashing would be terminated over the parapet wall, and a custom-fabricated prefinished steel coping cap would be installed in a color to match the attached standing-seam roof assembly.

For the laboratory area in the warmer climate, I again would install a two-ply vapor retarder adhered directly to the concrete deck. This typically would be eliminated from the assembly in the cold climate. The area then would receive two layers of rigid insulation properly staggered to counteract the effects of thermal bridging. Attachment would be accomplished using the same two-part urethane foam as previously described. A 1/4-inch-thick preprimed gypsum cover board then would be installed in a similar fashion. Understanding that the lab area may discharge harsh chemical compounds that adversely could affect an asphalt-based roof system, I would recommend the installation of an 80-mil-thick PVC membrane fully adhered to the cover board with the manufacturer's recommended membrane adhesive. Flashings and roof penetration details would be accomplished with careful attention to the manufacturer's recommended details to obtain a 20-year "no dollar limit" warranty for the owner.

With regard to the three-story storage and recreation area, assuming the roofs on these buildings are not directly incorporated into the fitness and recreation area, I would recommend a built-in-place extensive green roof system. I further assume drainage has been designed into the concrete deck. I recommend a multilayer liquid-applied membrane system that would offer the owner the confidence of a roof designed to incorporate redundancy into the waterproofing layers.

I would begin by priming the deck with an asphalt primer. Joints in the concrete would be sealed in a three-course fashion with liquid-applied rubber modified asphalt membrane and reinforcing mesh. I then would install 90 mils of liquid-applied rubber modified asphalt membrane to the prepared deck surface. A layer of reinforcing mesh would be installed in an additional 125 mils of rubber modified asphalt. Two layers of extruded polystyrene insulation would be installed in a loose-laid fashion. I then would install a felt root barrier, 1/2-inch-thick drainage mat and layer of filter fabric followed by 4 inches to 6 inches of engineered growth media. A variety of sedum plants would be planted in a 2-per-square-foot density. Plant species would be determined by the U.S. Department of Agriculture Plant Zone Table.

This system would help the owner with additional LEED accreditation points for green building design and stormwater management.

Kent Tolley

One of the criteria given for this project's design is to achieve Platinum-level certification. This presents challenges not usually faced when recommending a roof system design. There are several shades of green, as measured by the U.S. Green Building Council (USGBC) through its LEED rating system. As of 2005, only eight buildings in the U.S. had achieved a Platinum rating.

With the basis of design for the roof, there needs to be a balance between providing a long-term roof system and meeting the point requirements for a LEED Platinum building. Both goals could conflict with each other. Providing the best roof system for the project might not qualify for points for the project being designed.

With that said, I would roof this building using the following methods and materials.

The entry/reception area would have an R30 vented nailbase insulation (19 percent post-consumer recycled content and 15 percent post-industrial recycled content). The insulation would be fastened to a recycled metal Z section, which is fastened on top of the metal and into the beams to prevent interior fasteners from penetrating the deck. Then, I would install a 50-year synthetic rubber slate tile made of 100 percent recycled industrial rubber and plastic. I would install roof-mounted solar photovoltaic panels to supply an additional source of electricity.

The four-story office area would have two layers of 2 1/2-inch R30 (19 percent post-consumer recycled content and 15 percent post-industrial recycled content) polyisocyanurate insulation mechanically fastened to the deck. Then, I would install a layer of preprimed gypsum board with a foam adhesive according to FM I-90 requirements. I would install two layers of heavy modified base sheet in volatile organic compound- (VOC-) compliant cold adhesive and modified smooth cap sheet in VOC-compliant cold adhesive. Then, I would install an ENERGY STAR®-approved soybean-based white reflective coating.

The two-story laboratory area would have two layers of 2 1/2-inch, R30 (19 percent post-consumer recycled content and 15 percent post-industrial recycled content) polyisocyanurate insulation installed with a foam adhesive according to FM I-90 requirements to the concrete deck. Then, I would install a layer of preprimed gypsum board with a foam adhesive. I would install two layers of heavy modified base sheet in VOC-compliant cold adhesive and modified smooth cap sheet in cold adhesive. Then, I would install a locally supplied white gravel surface in VOC-compliant cold adhesive. The gravel surface is used to protect the roof membrane from potential waste that could come from the laboratory operations. I would install a walkway for access to rooftop units.

The three-story roof area would have a total green roof system installed over the concrete deck. The system would be:

  • Roof membrane—I would use hot fluid-applied, rubberized asphalt produced with a minimum 25 percent recycled content. I would apply the system in two coats, with a layer of fabric reinforcement between layers, to a thickness of 215 mils.
  • Root barrier—I would install a root barrier to prevent roots from penetrating the roof membrane.
  • Insulation—I would use extruded polystyrene with an R-value of 30 loose-laid over the root barrier.
  • Drainage mat—The drainage mat is to provide for water drainage and water storage. Mats should be made of 100 percent recycled polyethylene, molded for drainage.
  • Filter—I would install a filter fabric, soil and vegetation.

Your opinion

If you would like to share how you would approach roofing these fictional buildings, e-mail your response to or mail your response to Professional Roofing, 10255 W. Higgins Road, Suite 600, Rosemont, IL 60018. Responses will be posted on

Krista Reisdorf is managing editor of Professional Roofing magazine.


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