How would you roof this facility?

When installing a roof system on a building, often contractors have a variety of roof system options available. Different roofing contractors would approach the same project in different ways, and all the approaches would produce a viable roof system.

Professional Roofing presented NRCA member roofing contractors with parameters for a fictional building and asked them how they would roof the building and to explain their decisions.

Following are the characteristics of the fictional building:

• Located in the central U.S. (Missouri, Arkansas, Tennessee), the building complex houses a medical center and health and fitness center.
  
  
• The two-story medical office complex has a concrete roof deck, as well as an adjacent four-story building with additional offices and occupied space.
  
  
• The four-story offices and lab space have steel roof decks and an 18-inch (457-mm) parapet wall perimeter. There also is one isolated section with parapets on all four sides, a steel roof deck and interior use requiring sound attenuation.
  
  
• A two-story recreational space includes a gymnasium and attached pool areas, including a pool area isolated inside with floor-to-ceiling wall partitions. All areas have steel roof decks with gradual sloped radius curves, low-profile edges on the sides and curved ends.
  
  
• A 1 1/2-story multipurpose area for exercise, track, racquetball, etc., has a low-slope steel roof deck with 18-inch (457-mm) parapets.
  
  
• A one-story entry and food/beverage/lounge area has a steep-slope, wood plank, tongue-in-groove roof deck and needs deck insulation.

The following contractors contributed to the article: Rick Birkman, president of Texas Roofing Co., Austin; Leticia Elias, CC-RRC, president of Aztec Roofing & Sheetmetal Corp., Houston; Doug Fields, senior vice president of Certified Roofing Systems, Bladensburg, Md.; Will Fort, president of Fort Roofing & Sheet Metal Works Inc., Sumter, S.C.; and Mike Herlihy, partner and executive vice president of Olsson Roofing Co. Inc., Aurora, Ill.

Rick Birkman

Because the project is located in a southern climate, my proposal would be based on energy efficiency while creating robust roof systems that should last for decades. Although the initial cost certainly would exceed that of a more conventional specification, I believe the life-cycle costing, as well as the energy savings realized over time, would more than justify the initial cost. It is important to note that though I am a proponent of newer technology that promotes and encourages energy efficiency, I am not in favor of sacrificing a roof system's waterproofing integrity to further this goal. I assume a minimum R-value of 19 is required and all sloping to drains is in the deck.

With regard to the two-story medical office, it appears this roof area will be within view of, and possibly accessible by, the four-story office building. Therefore, I would put a vegetated roof on this area. Over the concrete deck, I would install a polypropylene felt that would soften the concrete's rough edges, followed by an 80-mil- (0.08-inch- [2-mm-]) thick PVC membrane with hot-air-welded seams. All walls, curbs and penetrations would be flashed, and the roof would be water-tested. Then, a 51-mil- (0.05-inch- [1-mm-]) thick protection membrane and drain mat would be installed. The soil medium, at a minimum depth of 6 inches (152 mm), would be installed, and vegetation native to the area would be planted.

Because the four-story office building is taller and getting hot asphalt at the proper equiviscous temperature to the point of application may be more difficult, I would try to stay away from installing asphalt on the roof.

I would begin by mechanically fastening two layers of 2-inch- (51-mm-) thick polyisocyanurate roof insulation to the deck. A layer of DensDeck Prime set in adhesive would be set over the insulation. The roof system would consist of a 160-mil- (0.16-inch- [4-mm-]) thick, triple-reinforced modified base sheet that would be set in cold adhesive with heat-welded laps.

The cap sheet would consist of a 140-mil- (0.14-inch- [4-mm-]) thick dual-reinforced, fire-rated cap sheet with an acrylic top coat that meets the U.S. Environmental Protection Agency's ENERGY STAR® reflectivity standards. The cap sheet would be set in cold adhesive with heat-welded side laps.

Because this building will be accommodating a lab facility and featuring the penetrations and exhaust residue common in such a facility, I strongly would consider protecting the roof system from foot traffic and chemical contaminants that will be exhausted onto the roof. This would be based on the number and type of penetrations and chemicals exhausted.

At the section requiring sound attenuation, I would fill the steel deck's flutes with batt insulation before installing the modified bitumen roof system.

With regard to the two-story recreational space, typically in our area, we are not concerned with vapor retarders. So assuming one is not required, I would mechanically fasten 3-inch- (76-mm-) thick polyisocyanurate roof insulation to the deck. I would cover the insulation with two layers of 40-mil- (0.04-inch- [1-mm-]) thick, high-temperature grade, self-adhering membrane. If the radius were gradual enough, I would install a 2-inch- (51-mm-) high, 16-inch- (406-mm-) wide double-lock standing-seam roof. If the radius were too severe, I would install an 18-inch- (457-mm-) wide, high-seam tee panel. Although the panel finish would be the owner's decision, I would recommend the new cool colors on the market that meet ENERGY STAR requirements.

For the multipurpose area, I would mechanically fasten two layers of 2-inch- (51-mm-) thick polyisocyanurate roof insulation to the steel deck. I then would install one layer of 1/2-of-an-inch- (13-mm-) thick wood fiber roof insulation in Type IV asphalt. The roof system would consist of a modified base sheet set in Type IV asphalt. The cap sheet would consist of a 140-mil- (0.14-inch- [4-mm-]) thick, dual-reinforced, fire-rated cap sheet with an acrylic top coat that meets ENERGY STAR standards.

With regard to the one-story entry and lounge area, I will assume the use of a tongue-in-groove deck indicates the deck will be exposed from the underside, so I would recommend installing 16-gauge Z purlins attached to the rafters at 2-foot (0.6-m) centers up slope. I then would install 3-inch- (76-mm-) thick polyisocyanurate between the purlins. I would cover the insulation with a 40-mil- (0.04-inch [1-mm-]) thick, high-temperature grade, self-adhering membrane. I would install a 2-inch- (51-mm-) high, 16-inch- (406-mm-) wide double-lock standing-seam roof system with the clips fastened to the Z purlins. I then would make the same finish recommendation to the owner as stated earlier.

Leticia Elias

I also am an enthusiast of roof systems that will enhance our environment. The hybrid roof systems I propose take into consideration the use of the building and its structural design.

First, these roof systems should satisfy minimum code requirements for the state in which the building is located. Also, all detail work will be performed according to the specific manufacturers' requirements, including drainage, parapet wall flashings and roof penetrations.

For the two-story medical office complex, I would recommend a hybrid system comprised of individual components and Hydro-Stop Inc.'s PremiumCoat roofing and waterproofing system. I would fully adhere 1-inch- (25-mm-) thick polyisocyanurate insulation board with polyurethane adhesive to the structural concrete deck and, if the deck is not sloped to drains, install a tapered insulation system to specified drain design as required. I then would install 1-inch- (25-mm-) thick DensDeck mopped in with Type III asphalt and a two-ply fiberglass Type IV membrane felt mopped in with Type III asphalt. A foundation base coat would be applied, and nonwoven reinforced polyester fabric embedded in the base coat, as well as a second foundation base coat over the fabric. For the surface finish, I would install PremiumCoat, achieving 45-mil (0.05-inch [1-mm]) total thickness.

For the four-story office and lab space, I would recommend an SBS-modified bitumen system. I would mechanically fasten 2-inch- (51-mm-) thick polyisocyanurate insulation board to the steel deck and, if the deck is not sloped to drains, install a tapered insulation system to specified drain design. I then would install 1-inch- (25-mm-) thick DensDeck mopped in with Type III asphalt and a two-ply fiberglass Type IV membrane felt mopped in with Type III asphalt. A granular-surfaced, SBS-modified bitumen cap sheet would be mopped in with Type III asphalt. The metal will include installing 24-gauge prefinished galvanized coping at the parapet wall.

For the two-story recreational space, I would recommend a hybrid system. I would mechanically fasten 2-inch- (51-mm-) thick polyisocyanurate insulation board to the steel deck and install a tapered insulation system to specified drain design. I then would install 1-inch- (25-mm-) thick DensDeck mopped in with Type III asphalt and two-ply fiberglass Type IV membrane felt mopped in with Type III asphalt. A foundation base coat would be applied, and nonwoven reinforced polyester fabric embedded in the base coat would be installed with a second foundation base coat installed over the fabric. For the surface finish, I would install PremiumCoat, achieving 45-mil (0.05-inch [1-mm]) total thickness. I then would install a waterproofing system, achieving 60-mil (0.06-inch [2-mm]) total thickness, and a green roof system on top of the waterproofing system. The type of green roof system installed will depend on landscape selection, drainage and weather conditions.

For the 1 1/2-story multipurpose area, I would mechanically fasten 2-inch- (51-mm-) thick polyisocyanurate insulation board to the steel deck and install a tapered insulation system to specified drain design. I then would follow the same procedure mentioned earlier. After embedding silica sand onto the finish coat and waiting for it to dry, I would install a TrafficCoat system—a coating used with the PremiumCoat system—to desired color. Metal will include installing 24-gauge prefinished galvanized coping at the parapet wall.

For the one-story entry and lounge area, I would recommend installing the required insulation above the tongue-and-groove deck, consisting of a nail-base insulation composed of 7/16-of-an-inch (11-mm) oriented strand board adhered to polyisocyanurate insulation. I then would install a self-adhering polymer-modified bitumen vapor retarder to the wood deck and cover with a tile roof system as per manufacturer recommendations. In this manner, the durability and aesthetic value of the entire project continue.

Doug Fields

The low- and steep-slope roof areas on this project are assumed to meet or surpass all building-code requirements and designed to withstand the loads imposed.

There are many roof systems suitable for this project, including built-up roof (BUR) systems and single-ply roof systems. In the interest of variety, I propose the following roof system for this project. My approach especially is useful where access is limited (such as high-rise buildings) or the noise, fumes and odor of asphalt heating equipment is a consideration.

On the low-slope roof areas, I would install tapered polyisocyanurate insulation. The insulation would be attached to the structural deck using dual-component polyurethane adhesive. The adhesive would be applied using a powered dispensing device at a rate that will achieve the designed wind-uplift requirements. This attachment method requires the use of insulation panels that are no more than 4 feet by 4 feet (1 m by 1 m) in size. The minimum insulation thickness will meet design requirements. On the roof area where sound attenuation is required, additional insulation over the structural deck may be an option.

Over the insulation, I would install a self-adhering modified bitumen base sheet. The insulation requires a factory-primed facer to ensure proper adhesion of the base sheet.

Over the base sheet, I would install a torch-applied, granule-surfaced, modified bitumen membrane. Vertical-to-horizontal transitions, such as parapet walls and curbs, will be flashed using multiple layers of smooth- and granule-surfaced modified bitumen membrane. On areas with significant foot traffic, the addition of walking surfaces or pavers is a good idea.

On the steep-slope roof areas (moderate radius curve), I would mechanically attach polyisocyanurate insulation to the steel deck. The insulation would be the proper thickness to achieve the designed R-value. I then would install a self-adhering modified bitumen base sheet over the insulation. Again, the insulation panels should be no more that 4 feet by 4 feet (1 m by 1 m) in size and require a factory-primed facer to ensure proper adhesion of the base sheet. A slip sheet or rosin paper would be placed over the base sheet, and a standing-seam metal roof system would be installed. The metal panels would be attached using clips and mechanical fasteners long enough to penetrate the structural steel deck.

Will Fort

For the two-story medical office complex, I would prime all concrete roof decks and solid mop 1/4-of-an-inch- (6-mm-) per-foot tapered perlite roof insulation system with either perlite or polyisocyanurate fill. This would, of course, be sloped to interior roof drains. I then would furnish and install a three-ply Type IV fiberglass felt BUR system with an SBS-modified cap sheet.

With regard to the four-story office and lab space, I assume all steel roof decks are structurally sloped. I would mechanically attach a base layer of 2-inch- (51-mm-) thick polyisocyanurate roof insulation and solid mop a top layer of 3/4-of-an-inch- (19-mm-) thick perlite roof insulation. I would install 4- by 4-foot (1- by 1-m) sumps at interior drains and furnish and install the same three-ply and cap specifications as stated earlier.

At perimeters, I would install one-ply Type IV fiberglass felt as backer sheet and a top ply of SBS-modified bitumen base flashing. At one isolated section, I would install fiberglass insulation in the bottom flute of the deck before attaching the 2-inch- (51-mm-) thick polyisocyanurate insulation.

I would use the same methods and materials when installing a roof on the 1 1/2-story multipurpose area.

For the two-story recreational space, I would install one layer of mechanically attached 5/8-of-an-inch- (16-mm-) thick DensDeck Prime to receive the vapor retarder. I then would install two plies of Type IV felt with asphalt to act as a vapor retarder. A two-ply SBS-modified bitumen roof system would be installed.

With regard to the one-story entry area, I would mechanically attach single-layer rigid insulation to the tongue-and-groove deck. (If the deck thickness is between 2 1/2 inches [64 mm] and 3 inches [76 mm], this can be accomplished with mechanical fasteners.) I then would mechanically attach a layer of synthetic underlayment through insulation into the tongue-and-groove deck. I would furnish and install a 16-inch- (406-mm-) wide architectural metal roof system using bearing plates at clip locations with all related trim.

A nail-base insulation could be used or substituted over the tongue-and-groove deck instead of standard rigid insulation.

Mike Herlihy

I assume the metal deck on the four-story office and lab is structurally sloped to interior drains. I also assume the sound-attenuated area has its own drainage and the two-story recreational space is an open steel arched structure with an acoustical deck.

Other assumptions I have made include that the heating, ventilating and air-conditioning system has ducted returns; roof decks and structures are designed for a 15-pounds-per-square-foot roof dead weight allowance; overflow drainage is provided at each roof system via independent drains or overflow scuppers; because of multistory use, one-, 1 1/2- and two-story areas will require a one-hour fire assembly; and all roof systems are required to have a Class A external fire rating.

I also assume no FM Global ratings are specified; the area is susceptible to hailstorms and ice storms; the medical center offices do not house any day surgery or critical care or emergency care services that would require an increased use importance factor greater than 1.00; an architect will be available to review the roof system, details and configurations; the building is managed by a property manager; and roof management and system maintenance will be passive during the life and use of building. Finally, I assume no staff on-site is trained to attend to roof system maintenance or inspections, and property proforma requires a 15-year life-cycle expectation.

On the two-story medical office complex with a concrete deck, I would install a 60-mil- (0.06-inch- [2-mm-]) thick ballasted EPDM roof system over a 3-inch- (76-mm-) thick minimum tapered polyisocyanurate insulation system loose laid over the concrete deck. A vapor retarder should not be required here based on the use, location and deck type. I would provide paver walkways from the roof hatch to and around the rooftop unit and concrete pavers at exterior corners.

A 60-mil- (0.06-inch- [2-mm-]) thick ballasted EPDM roof system over two layers of a 2-inch- (51-mm-) thick polyisocyanurate insulation system over the sloped metal roof deck would be installed on the four-story office and lab space. A vapor retarder also should not be required here. In the past, I would have incorporated rigid fiberglass with DensDeck at the acoustical area. However, with rigid fiberglass no longer available, I now likely would add one layer of 5/8-of-an-inch- (16-mm-) thick DensDeck over 1-inch- (25-mm-) thick perlite over acoustical flute filler over the acoustical deck under the two layers of polyisocyanurate. I would provide paver walkways from the roof hatch to and around the rooftop unit and concrete pavers at exterior corners.

For the two-story recreational space, I would install a Sarnafil fleeceback G410 Décor-rib membrane fully adhered over 1/4-of-an-inch- (6-mm-) thick DensDeck mechanically attached through two layers of 2-inch- (51-mm-) thick polyisocyanurate insulation over a 10-mil- (0.01-inch- [0.25-mm-]) thick visqueen vapor retarder. This would be installed over a 5/8-of-an-inch (16-mm) type "X" gypsum board fire barrier over acoustical flute filler in the flutes of the acoustical deck.

With regard to the 1 1/2-story multipurpose area, I would install a 60-mil- (0.06-inch- [2-mm-]) thick ballasted EPDM roof system over two layers of 2-inch- (51-mm-) thick polyisocyanurate insulation over a 10-mil- (0.01-inch- [0.25-mm-]) thick visqueen vapor retarder. This would be installed over one layer type "X" gypsum board over a layer of 1-inch- (25-mm-) thick perlite (for better sound attenuation) over acoustical flute filler nested in the acoustical deck.

I would install a copper standing-seam roof system over one layer of No. 30 felt for the one-story entry and lounge area. This would be installed over one layer of a self-adhering polymer-modified bitumen water barrier over 3/4-of-an-inch- (19-mm-) thick plywood mechanically attached over two layers of 2-inch- (51-mm-) thick polyisocyanurate insulation over the tongue-and-groove wood roof deck.

These assemblies will provide value, long-term performance and minimal maintenance.

Your opinion

There are a variety of roofing options that have not been mentioned in this article. If you would like to share how you would approach roofing this fictional building, e-mail it to professionalroofing@professionalroofing.net or mail it to Professional Roofing, 10255 W. Higgins Road, Suite 600, Rosemont, IL 60018. Responses will be posted on www.professionalroofing.net.

Krista Reisdorf is associate editor of Professional Roofing magazine.