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FIELD TECHNIQUES - Why Didn't I Think Of That?

   Author: MetalMag

RETROFIT METAL ROOFING OVER OLD, flat roof structures is growing more common, particularly as time and money invested in the upkeep of aging, flat, leaky roofs gets out of hand. Roofing workers are installing fully engineered reroof framing systems that can meet all required slopes, eliminating flat roof leaks. And some even have the machines to rollform their own framing studs, shoes, tracks and panels.

Uncommon, however, is a retrofit framing structure over a new flat roof - a technique only used occasionally until two years ago. That is when Florida architect Bayne Collins specified a retrofit light-gauge framing system in place of a truss system for the 130-unit Adagio condominium resort project in Blue Mountain Beach, Fla. The project encompasses several 4- and 5-story condominium buildings just yards from the Atlantic Ocean.

Collins, with offices in Panama City, Fla., worked with Ameritech Enterprises, Inc., a Panama City-based roofing company with a track record for installing retrofit metal roof systems on school renovations where Collins had served as architect.

At first glance, it might appear the costs of designing a retrofit system over a new flat roof might be questionable. But the Adagio project and two others since that installation have brought some surprising results and what is certain to become a new trend in framing systems for metal roofing on new building projects.

The Adagio retrofit on a new flat roof called for a slope purlin system with a metal deck installed over a flat structural concrete building system. The retroframe system was provided by Reroof America Corp., Tulsa, Okla., and was chosen over a truss system. The results were interesting.

A retroframe metal roof brings aesthetics to a building that a flat roof cannot achieve.

According to Ameritech Enterprises, it took about one-third the time to install, allowing the buildings to be completed two weeks faster than a conventional truss system. Second, the use of a retroframe system eliminated about 40 percent of the cost associated with crane rentals necessary to erect a truss system. Third, the retroframe system was spaced on 4-foot (1.2-m) centers versus the typical 2-foot (0.6-m) on-center spacing for a truss system, providing a substantial amount of rooftop storage space. And fourth, the retroframe system required 50 percent fewer fasteners than a truss system.

This system also saves on labor costs. In contrast to a truss system where each form must be installed sequentially, the retrofit system allows a contractor to spread 15 to 20 workers around the roof to work on various sections of the system at one time. In addition, the use of the retrofit system eliminated concerns about installing trusses atop a concrete deck that might not be flat, a fairly common concern, particularly with concrete poured later in the day. It's difficult to install a truss system if the concrete deck isn't flat or specifications are off.

"If the prefabricated truss is different than [how] the roof was actually built or the roof isn't square, then the truss won't fit," notes Kelly Sixkiller, project coordinator for Reroof America. "And because trusses are prefabricated and shipped in 16- or 18-gauge galvanized steel, the contractor is faced with a difficult challenge in attempting to field modify them."

Alterations to trusses only should be made under the guidance and supervision of a licensed engineer, preferably the original truss designer. While many of the components of the retroframe system are precut to length, they can be field assembled within adjustable ranges, which readily allows for field adaptation to compensate for common construction irregularities, Sixkiller notes.

The retroframe system incorporates adjustable height ranges as required by each project.

Similar to a truss system, the adjustable framing system consists of steel top, bottom and web members that are sized and selected specifically for each project. However, unlike a truss system, the retroframe system incorporates adjustable height ranges as required by each project with atypical total adjustability of plus or minus 3 inches (76 mm). The proper elevation of the top member is achieved by an adjustable top clip or sliding the web member vertically on the top or bottom member.

The adjustable framing system web members typically are a 16-gauge cee member precut to the exact length required to allow proper function of adjustable elements. The intermittent bottom members are factory precut, and the bottom flange of the bottom member is factory prepunched for attachment to the existing structure. All bottom members are sized and selected to distribute the new roof loads to the existing structure without over stressing the bottom member or exceeding the allowable compressive strength of the roof.

The adjustable top clips and bottom members also eliminate the need for fire permits required for costly and time-consuming field cutting of vertical framing members for truss systems.

The retroframe structure eases some of the insurance concerns associated with flat roofs, as well. Problems with hot tar and flying gravel are no longer a concern. This can reduce insurance costs for casualty and liability resulting from injuries sustained from flying gravel and debris, as well as employees burning themselves on hot tar kettles.

Overall, these projects--whether new or retrofit--are easy to plan and install. An architectural or engineering firm designs the retrofit roof system utilizing information about structural framing members and structural standing-seam roof systems available from various qualified suppliers. The design usually is done with input from the manufacturers of the standing-seam roof system.

The architect works with a supplier of the complete retrofit system who provides for an investigation of the existing roof conditions, including structural framing and penetrations through the roof, mechanical equipment and special conditions. They conduct an engineering study to determine attachment requirements, framing requirements, water drainage, optimum pitch of the roof system and the most cost-effective products. For example, Reroof America suggested altering some architectural details in the Adagio project, eliminating ridge beams and valleys to reduce material requirements, including the number of uprights.

The retroframe structure eases some of the insurance concerns associated with flat roofs.

Once the engineering study is finished, a complete work up of all materials, including the standing-seam roofing, is done. The architect uses standardized sections and details with computerized drawings and estimating methods to provide a complete design that meets code requirements and the unique needs of the project. The retroframe manufacturer and metal roofing supplier can recommend a qualified installer. The architect may require weather-tightness warranties for the entire retrofit roofing project. Should the job be bid and not negotiated, the specifications should stipulate any contractor bidding the project be approved by the manufacturer of the retrofit system and metal roofing material supplier.

In designing the Adagio, Collins chose an Englert Series 1300, 0.032-gauge sandstone aluminum roof, which meets wind and uplift requirements set by the 2003 Florida Building Code, Dade County uplift testing, UL uplift standards and ASTM uplift standards. That choice brought kudos from the owner, particularly when the 150-mph winds of Hurricane Ivan left the retrofit system and its standing-seam roof unscathed while devastating buildings and roofs with other systems only yards away.

Collins and Ameritech Enterprises developed the same system for the Celadon, a 24-story condominium building and the first high-rise built in Panama City Beach after Florida Building Codes were updated following Hurricane Andrew in 1993. "We looked at a truss system for the building but realized a retrofit would be more flexible and cost effective," Collins notes.

He chose an aluminum panel because of its performance over steel in saltwater environments. "You have to be careful with the systems you use to guarantee waterproofing against wind driven rains in high-wind environments," he adds. "To be certain, the owner retained a waterproofing consultant who worked with us through the design conditions, including door testing and flashing that would stand up against the elements."

"A retroframe metal roof brings aesthetics to a building that a flat roof cannot achieve," notes Yoosef Lavi, president of Lavi & Associates, Dallas, and the engineer who was commissioned to produce an ASCE engineering analysis of what would be required for the Celadon to withstand hurricane-force winds. Lavi considers a number of factors in producing the report, including the required wind-speed loads, geometry and geography of the building, the building's exposure, area weather history and the pitch of the roof.

"If we had used EPDM and river rock to hold it down, the high winds from hurricanes in 2004 would have peeled away the membrane and thrown the rock off the roof," Lavi explains.

In colder climate, the issues are somewhat different but the advantages of the retroframe metal roof are the same, Sixkiller observes.

Corporate parks with the typical office buildings have flat roofs where ice and snow build up in the corners, creating pools when they melt. Inevitably, this process causes leaks, and the owners get fed up with the high cost of maintenance. Architects should be thinking of replacing those designs with a retroframe system and standing-seam roof. It will jazz up the look, add value to the building and save a lot of headaches associated with leaks.

This holds true for new school construction, as well. School architects practicing in colder climates should consider a retroframe system because it's quick and easy to install; eliminates the inevitable concerns about leaking associated with flat roof design; and, above all, looks great.

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