Photo courtesy S-5!
Transferred from the U.S. Air Force to a group of volunteers in 1994, Wings Over the Rockies Air & Space Museum is located at the former Lowry Air Force Base in Denver, Colorado. Today, the museum boasts more than 16,908 m2 (182,000 sf) of hangar space full of iconic aircraft, space vehicles, artifacts, military uniforms, and more. When the existing corrugated metal roof on the structure had reached its useful lifespan, the project team retrofitted it with a curved standing-seam roof.
The challenge
The challenge was to remove and replace a large radiused roof during the cold winter months, while keeping the museum open for its patrons. Increasing the difficulty was the shape and height of the roof—curved and more than 30 m (100 ft) off the ground with a circumference measurement from eave-to-eave over the top of the barrel at 308 linear feet.
Another challenge was to meet the standards of the city and County of Denver’s Landmark Preservation Commission—to maintain the same historic look of the building with the new roof system.
The solution
Project consultant Alec Garbini and AH Architecture were brought on board to oversee the project. They were tasked with finding a roofing contractor who could help custom-design and construct a system, and handle the removal and replacement of the large radiused roof.
A Colorado-based roofing contractor was selected and proposed to leave the existing corrugated metal roof in place and retrofit a new lightweight roof system. This approach would allow the museum to remain open while the new roof system was constructed.
Mill-finished galvalume material was selected for the standing-seam panels to preserve the look of the old hanger and meet the criteria of the historical society.
The roofing contractor fabricated 25,000 linear feet of 152-mm (6 in.) high z-purlins from 16-gauge steel. Installers attached the z-purlins through the existing corrugated deck and into the main frame of the building. By securing the z-purlins to the main frame, they transferred the load of the new roof system and raised the new fastening point 152 mm higher.
Next, they laid down 152 mm of new ridged insulation nested tightly between the newly secured z-purlins and chose to use two layers of 76 mm (3 in.) foil-faced polyisocyanate insulation board, providing the building with an added R-value of 38. Finally, installers enclosed the insulation and z-purlins with a high-temperature ice and water shield membrane.
The roofing contractor manufactured the 94-m (308-ft) long panels in four separate lengths with each panel being 23 m (77 ft) long. They designed a custom expansion joint end-lap-detail to attach the panels together, making them span the full length of the barrel.
Winslow Crane Service hoisted the panels and the panel-forming machine up to the roof level, suspending it a few inches off the roof deck where 8584 m2 (92,400 sf) of roofing panel was manufactured utilizing the 457-mm (18-in.) wide 44 mm (1 ¾ in.) snap seam profile. The panels were curved around the radius of the barrel as each one was installed.
A metal roofing systems provider supplied the 610-mm (24-in.) wide, 24-gauge, satin-finished galvalume roofing coils to make the standing-seam panels, as well as more than 300 flat sheets to custom fabricate the flashings, trims, and components for the project.
Once the new roof was installed, the project consultant observed heavy snow sliding off the new satin-finished metal roof panels in greater volume than the pre-existing corrugated roof panels. He advised something would need to be done to control rooftop avalanche conditions.
A metal roofing attachment provider designed and engineered a snow retention system to mitigate the avalanche problems. Manufactured from high-tensile, certified aluminum and extensively tested for load-to-failure results, the snow retention system reduces the risks associated with rooftop avalanches and complements the look of the roof, with a clean appearance and perfect color and finish-matching, all designed to last the life of the roof.
