Ahead of the Curve
Ahead of the Curve
curved roof without the expense of beam or steel construction,
the designer knew the answer was trusses.
Dennis Rainho of YRA Design said his customer wanted “a house that doesn’t look like your typical south Florida house.” Inspired by West and West Coast styles in Colorado and California, the homeowner asked Rainho to give a “contemporary look” to a concrete-block house, designed to withstand Florida’s hurricane-force winds. Namely, he wanted a curved roof. Rainho remembered his first reaction: “I said to the owner, ‘It’s going to be better if we do this with trusses, because it’s going to be more economical in the long run.’”
The construction methods typically used in West Coast housing—timber, laminated beams, steel—are generally more expensive than wood, Rainho explained. Those materials can make curve easier but, “if we do soft curves,” Rainho told the homeowner, “we can probably do this using trusses.” Trusses could meet all the requirements of the project: within the owner’s budget, they could support a curved exterior roof, interior ceilings with faux beams for a striking, exposed-structure look and web member spacing designed to accommodate the large ducts needed for air conditioning.
A real beam roof, Rainho said, just wouldn’t work. A truss roof was perfect, but that didn’t mean it would be easy.
Nuts & Bolts
“My immediate thought,” recalled Ruth Haggerty, P.E., of Renewable Design, was that the trusses weren’t oriented correctly. She anticipated they would run along the curve rather than across it. When Rainho assured her the architecturals were correct, she realized it made sense—the design would make it much easier to produce and install the trusses. It would also make her job as the structural engineer on the project a much bigger challenge. The design, she said, was “easier for the trusses, but much more difficult for the engineering.”
One key problem, Haggerty said: “I couldn’t figure out a way to do a straight ledger. I thought long and hard on it.” What she eventually came up with took the truss design even further than Rainho had originally imagined. “Her idea was to put the trusses staggered along the curve,” Rainho said. “From the front of the house to the back of the house, [as the trusses] hit the exterior walls, they start dropping down.” To achieve the staggered-height setup, Haggerty designed a two-foot ledger section for each truss. It was enough area to make the roof system structurally sound and provided enough space to accommodate the truss hanger.
“It’s definitely very challenging,” said Ryan Spencer, the truss designer in A-1 Roof Trusses’ custom division who worked from Rainho and Haggerty’s designs. Such a unique system called for extra attention to detail. “There’s a lot to actually sit there and figure out,” Spencer said.
For example, a curve is not an easy thing to design in a truss world more typically focused on rectangles and triangles. The fact that the trusses supporting the curved roof run parallel to the curve helped, because it meant the top chord of the truss didn’t need to match the curve of the finished roof-line. That, Spencer observed, would have been a huge design challenge; and, he added, “building it would have been a nightmare!”
Instead, the designs Rainho and Haggerty passed to Spencer called for a more routinely-constructed truss that could then be adjusted during installation. “We did flat trusses, all the same depth,” Spencer explained, set at different heights against the walls and supporting girders. With the girders at fixed heights and the trusses staggered, framers could “adjust the bearing height to form the curve in the field.” Each truss was trimmable so that framers could fit it into the hanger and make adjustments as needed along the way. The design, Haggerty confirmed, gave framers “the most flexibility as they werebuilding to make sure the elevations were correct.”
Providing that flexibility on the installation side meant a lot of calculation on the design side. “Each and every truss, I had to figure out what height it was going to bear at,” said Spencer. Fortunately, he had the right tools. “We have this nifty little calculator,” Spencer explained. “It breaks down that curve in segments.” Spencer entered details from Rainho and Haggerty’s plans, and the calculator provided the height and pitch of each individual segment of the curve. That information went into the truss design software so that the trusses fit the curve Rainho and Haggerty had worked out.
“It was a lot of nuts and bolts,” Spencer said. He estimates he put four or five days into the design— a lot, even for the complicated projects that are typical of the work in the custom department. “If this job didn’t have those curves and that roof like it did, and the ceiling conditions, I could have had this job designed in a day and a half.”
As it was, finalizing the designs and collecting all the approvals meant it was nearly a month before anything was ready for the shop.
Special All Around
Spencer said everything “flowed together quite well,” as he, Haggerty and Rainho worked through all the details of the designs. “There were critical bearing locations that we had to adjust to support these curved roofs,” Rainho recalled, but “we never went beyond small adjustments.” Anything he or Spencer suggested, Rainho said, Haggerty was able to work out by moving things a few inches one way or another.
“For the complexity of the job,” Haggerty said, “there have not been many revisions along the way.” The ones that did happen were important, though. For example, Haggerty recalled, it was at the truss design stage when one of the parapet walls was eliminated from the design entirely. The wall wasn’t functional, and it was completely hidden under the eave of the upper curved roof. “That was one of the biggest changes that came from [A-1, and] that saved us all a lot of effort,” Haggerty said. “Instead of the double truss,” which would have supported the parapet wall, they were able to alter the design and use “just a single girder” to support everything.
“It was quite a challenge,” Spencer summed up. It took “a lot of attention to detail to get everything right.” Especially because the curved roof itself wasn’t the only difficulty.
For Rainho, other issues arose in terms of structure size and cosmetic details. He said he’s done plenty of similar commercial projects but “one of the challenges of doing a house with a curved roof is that it’s one story.” The bigger the building—or the more stories you have to work with—the easier it is to curve the roof. The radius of the curve can be bigger and there’s plenty of space for additional flat and angled rooflines that can better manage water runoff, support loads from higher rooflines and actually close the envelope of the building.
In this case, even once the building envelope challenge was solved, there was still the inside of the house. Many of the beams that give the interior the contemporary exposed-structure look that the owner wanted are not actually structural, Rainho said. While that might take one thing off Haggerty’s plate in terms of engineering, it complicates things for an architectural designer.
“You have to make everything look functional, even if it isn’t,” Rainho explained. The goal is to “create a certain look” using one structural support system, but to make another structural system look plausible. Only a highly trained eye should be able to spot what’s cosmetic instead of truly structural.
For Haggerty, the curve challenge was balanced by the fact that the house has almost every roofline imaginable. “We did two layers of curves,” she said, beginning a long list of roof types, “we did a flat roof with a parapet above the garage, we did a pitched roof,” and gables, arches, slopes, and more. “Just about every roof style,” Haggerty said, “all in one roof!”
“It’s a special project all the way around,” Spencer agreed. From entry to garage, from ceiling to storage, each corner of the house had its own unique design complexities that the team was happy to see come together. With truss installation now complete, Haggerty’s reaction best sums up their collective assessment: “I was pleased with the whole process.”
A-1, founded in 1977, is one of the longest-operating truss manufacturers in Florida. It continues to serve the Southeast and is still owned and operated by co-founder John Herring.