Silent construction

• Photo courtesy of Cabral Roofing & Waterproofing Corp., Montebello, Calif.
• Photo courtesy of Cabral Roofing & Waterproofing Corp., Montebello, Calif.
• Photo courtesy of Cabral Roofing & Waterproofing Corp., Montebello, Calif.
• Photo courtesy of Cabral Roofing & Waterproofing Corp., Montebello, Calif.

Southern California Edison, Rosemead, Calif., provides electric power to about 13 million people per day and 430 cities and communities. Delivering power is no small task and involves 4,990 transmission and distribution circuits, as well as the work of more than 13,000 employees.

With so many people depending on Southern California Edison, when the company planned to reroof its headquarters building, it needed a roofing contractor it could trust to handle the task.

NRCA member Cabral Roofing & Waterproofing Corp., Montebello, Calif., bid the project and was awarded the job. Having worked previously with Southern California Edison, Cabral Roofing & Waterproofing was a natural choice to reroof Southern California Edison's headquarters building in Rosemead.

The reroofing project featured unique obstacles, including the challenge of performing construction in relative silence.

Not only was Cabral Roofing & Waterproofing reroofing a 163,000-square-foot (15143-m²) roof system, but it also was asked to perform the project without disturbing the company's senior executives, who were toiling directly below in their offices. This meant the roofing crew had to be conscious of noise, dust and odors.

Careful planning

To minimize the effects of the roofing work on the business operations of the building's occupants, Cabral Roofing & Waterproofing and Southern California Edison held strategy meetings to discuss material delivery and staging of equipment and material. One solution the roofing company devised was to seal intake vents to keep odors out of the building. In addition, Southern California Edison required Cabral Roofing & Waterproofing to work during the early morning or late evening as a strategy to help mitigate the noise problem.

"We had to be conscious of not making noise by carefully placing rolls and staging equipment in strategic areas," says Desi Cabral, vice president of Cabral Roofing & Waterproofing. "Loading and unloading had to be done during off hours because we had to work around Southern California Edison's schedule of meetings. Certain areas had to have work completed based on meeting schedules at the headquarters. Mistakes could not be made that would cause the work in that section to go beyond the agreed schedule."

In addition, Cabral Roofing & Waterproofing had to face challenges such as the fact that the roof assembly's structural deck consisted of a completely flat concrete slab; unique shape of the building with only two access areas; asymmetrical placement of existing roof drains, which made the installation of the tapered lightweight concrete more difficult; and limited height of the parapet walls. Because a factory-tapered insulation system was determined to be impractical, a lightweight insulating concrete tapered system was specified to provide positive drainage for the roof system.

Tear-off

The building had two existing roof systems that needed to be removed.

"The first existing roof system was over a concrete deck with a vapor retarder, 1-inch- (25-mm-) thick fiberglass insulation and a four-ply coal-tar-pitch roof system, as well as aggregate surfacing," Cabral says. "The second existing roof system consisted of expanded polystyrene tapered insulation with a 1-inch- (25-mm-) thick fiberboard and four-ply conventional built-up roof (BUR) system with aggregate surfacing."

The existing roof systems had to be torn off to expose the concrete deck, and removing the debris posed a challenge.

"The roof was approximately 55 feet (17 m) from the ground, and removing the old roofing material was difficult," Cabral says. "It required building five-story scaffolding with a chute to deliver the materials to a trash bin. Because of the thickness and type of insulation that existed on the previous roof system, cutting up the insulation caused massive debris particles that had to be controlled. The debris sometimes became clogged in the chute, requiring the materials to be cut into small pieces."

In addition, the project only had two locations where Cabral Roofing & Waterproofing could set up equipment.

"We had to carry everything from one end of the building to the other, which was challenging," Cabral says. "There was a great distance from the delivery point of the materials to the actual job site. It also was necessary to use four-wheel all-terrain vehicles on the roof to haul materials around the building and move the old roofing materials to the disposal chute."

Installation

After demolishing one of the four roof sections, Cabral Roofing & Waterproofing began installing a Johns Manville four-ply BUR system.

"Over the structural deck, we installed a 28-pound base sheet set in hot asphalt as a temporary roof and vapor retarder to immediately dry in the roof and protect the occupants and contents of the building," Cabral says. "The lightweight concrete was poured over the vapor retarder to maintain a minimum 1/8-in-12 (0.6-degree) slope. The insulating concrete tapered system varied in thickness from 3 1/2 inches (89 mm) to 14 inches (356 mm). Lightweight fill and insulation filler were used.

"A 72-pound inverted cap sheet was mechanically attached with lightweight insulating fill nails before three plies of Glas Ply® IV membrane were hot-mopped in asphalt," he continues. "The roof was finished with an aggregate surfacing set in a flood coat of hot asphalt, which was pumped up to the roof."

When it came to safety, the company was prepared.

"When working at the building's interior, which surrounded a courtyard, the crew used anchored safety cables with five-point harnesses," Cabral says. "In addition, the same safety equipment was used when working around the building's perimeter ledge because of the obstruction of the perimeter mansard."

Cabral Roofing & Waterproofing performed the roofing work during the rainy season, which was another obstacle during the installation process—especially because it was imperative the company take precautions to ensure each roof section was watertight at the end of each day. These efforts were put to the test one day.

"During a Saturday in October—which turned out to be Los Angeles' wettest October in three decades—we were in the process of tying in the last section over the newly poured lightweight concrete and battling the knowledge that a severe storm quickly was approaching," Cabral says. "The crew impressively tied in the last of the four-ply roof system less than 30 minutes before the storm hit. The storm dumped 3 inches (76 mm) of rain that night."

End results

Cabral is proud of his company's work, saying the roofing workers "successfully completed the scope of work—two weeks ahead of schedule—overcoming logistical, as well as environmental, hurdles to the building owner's satisfaction."

Cabral is not the only person who offers praise for the project. Nick Lovato, roof consultant for CyberCon Engineering, Centennial, Colo., says the challenging project was successful.

"The project went extremely well," he says. "The degree of difficulty was high because of the amount of debris that had to be handled, limited staging areas and maintaining the watertight integrity of the building envelope, among other challenges. The owner will receive excellent value for the roof system that was installed."

Mel Mitchell, project manager for Southern California Edison, also was impressed.

"Cabral Roofing & Waterproofing is one of the best roofing contractors in southern California," he says. "The crews don't require much supervision, and the workers follow the specifications, ask questions and have a high quality of workmanship."

Krista Reisdorf is associate editor of Professional Roofing magazine.

Project name: Southern California Edison Headquarters
Project location: Rosemead, Calif.
Project duration: August 2004-November 2004
Roof system type: Four-ply built-up roof system
Roofing contractor: Cabral Roofing & Waterproofing Corp., Montebello, Calif.
Roofing manufacturer: Johns Manville, Denver
Roof consultant: Cybercon Engineering, Centennial, Colo.