Plant remains functional as new building is built over old one

Engineered steel buildings have been marketed for decades as offering the advantages of clear-span structural framing, low-maintenance steel roofs, insulation values and control over a construction schedule. These factors favored this solution for replacement construction at the Alberta Plywood plant in Edmonton, Alberta.

The facility is a subsidiary of West Fraser Mills, Ltd., an integrated forest products company based in Quesnel, British Columbia. The workforce of 230 people at the 24-hour, 363-day facility produces 251 million sq. ft. of 3/8-in. plywood annually to rank the facility among the largest plywood producers in Canada. The project addressed the area encompassing the critical lay-up line, where the plywood is assembled, pressed and cut to size.

“We had several objectives for the project,” says Dan Lewis, Alberta plant manager. “Our primary goal was to replace an older wooden roof structure, improve heat and dust control, and provide better illumination of the working area. The project also would open up the work floor by removing some existing columns supporting the timber roof trusses of the existing building.”

Because the area was essential for continued production, the new construction was superimposed over the 16,000 sq. ft. of older space. Carefully coordinated demolition and removal of the original construction was then done from within the 28,000-sq.-ft. new building, the size of which was dictated by snow loading and an existing area within that was left intact.

“We had built similar projects at other mills,” Lewis said. “Sometimes the ongoing operations make building over the top the only solution.”

Six months of planning by company management, consultants and MCG Joint Ventures, an authorized Robertson Builder, preceded the work. Edmonton-based MCG had performed projects at the plant for 25 years for both the current and previous owners of the facility.

A complete package of steel building systems, designed to the requirements of the National Building Code of Canada (1995 Edition), the Alberta Building Code (1997 Edition), and other rigorous design standards, was engineered and supplied by Robertson Building Systems (

The mix of fully integrated building systems included a 22-gauge Robertson SSR standing-seam metal roof system, which has a UL-90 Wind Uplift rating and Factory Mutual approval as a Class 1 roof panel. Wall construction used 6-in.-thick, 3/4-lb.-density fiberglass mat with an integral factory-applied vapor barrier between 26-gauge exterior metal wall panels, and a white 29-gauge roof liner panel system added dust control.

The contractor used a 400-ton mobile crane fitted with 250 ft. of boom to set the new structural steel over the existing building. Tolerances were critical. At some points, the new columns between existing joists had only 3 in. of space on each side, and one left only 1/4 in. of clearance between the column face and an existing wall. Still others were set through the process equipment where their bases are carried by 20-foot-deep horizontal beams. Poor site conditions required 30-ft. concrete pilings at other points, in addition to the normal column footings and anticipated foundation construction.

“Robertson steel systems had absolutely zero fabrication errors,” recounts Tony Naccarato, principal, MCG Joint Ventures. “The quality was extremely impressive.”

The new construction's 10 ft. to 12 ft. higher vertical clearance allowed construction crews to work off the flat roof of the existing structure in a temporary “attic space” under the new roof. The space and firm footing was especially beneficial while installing the fire-sprinkler system, better air exchangers, and energy-efficient 400-W metal halide lighting that increased illumination to 48 ft.-candles on the production floor. The now metal-lined walls are insulated to R-20 and prevent the sawdust buildup of the past.

Construction extended from May through October, 2006, and two MCG crews, with a total of 24 people on two shifts, completed the demolition phase during the plant over the Thanksgiving holiday.

To other plant operators confronting a similar construction program at plants with around-the-clock operations, “Planning and thorough preparation up front are absolutely critical,” Lewis advises. “Using engineered steel building systems enabled us to clear-span the whole area. Other construction might not have allowed it within a reasonable cost.”

The only unforeseen problem in the new construction was heat buildup, attributed to the well-insulated walls. This has since been corrected with some fans that pull in cool air from another area of the plant.

The project demonstrates that quality-controlled materials, logical construction phasing and overall project management can allow a construction project to proceed even in immediate proximity to plant production lines.

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