Building Truss

Before the three massive beams were welded onto steel columns; before the 11 steel boots were welded to the I-beam; before the 33 tapered rafters were slipped into the boots, stretched upward like the wings of a butterfly, connected to the high beams, and tensioned by the steel cables; before any of this, there was a homeowner who simply wanted a nicer place to live.

What happened in the intervening years was not so simple. Countless discussions, drawings, and calculations were hashed out to identify how to achieve a functional, comfortable space within a uniquely dramatic structure as cost-effectively as possible. Demolition and framing began on some parts of the house even as rough schematics were fleshed out on others. Tiny models were made, studied, and rebuilt differently. Big models were built too, including a full-size mock-up of the 35-foot truss that stretched across the architect's office and was later foam-mounted and hung in a gallery.

The process was at times frustrating, always collaborative, and finally satisfying in its stunning conclusion. “You never know what you will learn from trying something new,” says remodeler Will Alphin of Alphin Design Build, Raleigh, N.C. “I gained technical knowledge from working with new products and materials, organizational knowledge from coordinating with many people,” and, he says, “a deeper appreciation of the role of the architect.” As difficult as the process sometimes was, Alphin says he never lost sight of the fact that Cannon Architects, also of Raleigh, “had a beautiful and bold vision that we all believed in.”

Photo Credit: JWest Productions (above), Rob Allen (inset)

The house stands out in architecturally traditional Raleigh not so much for its façade, but for its rear elevation. Situated on a U-shaped street where the streetcars used to turn around, the 1920 Craftsman bungalow appears at first glance to be more or less true to its humble roots, despite its new covered porch and large gabled dormer over the front door.

Peer around back, however, and you're in a sculpture garden. An inverted-pitch, or butterfly, roof soars to 30 feet at its highest point and provides a generous canopy over the L-shaped deck. The roof's asymmetrical spans are supported by an exposed truss system made of Douglas fir, painted steel struts, and stainless steel cables. The lines of the truss continue inside, revealed through high windows, and downward, via Douglas fir columns and a slender steel chimney.

Inside, although the addition consists of less than 900 square feet, it feels larger thanks to the scale of the new rooms, the reconfiguration of some existing rooms, the choice of materials, and the abundance of natural light. The old galley kitchen, for instance, was made slightly narrower yet extended and opened at the back to create a visual and physical flow to the new family room. Both bedrooms on the main floor have been expanded and given private baths. The master suite is both secluded and sunny, thanks to discretely placed windows and four interior clerestory windows it shares with the family room.

The floor of the family room is two steps lower than the kitchen area, and its height is further accentuated by the high windows and truss. The room also features built-in cabinetry, a site-built fireplace with cantilevered concrete hearth, and a built-in bench made of African ribbon mahogany. Another feature is the uninterrupted view to the wooded lot through huge windows and almost invisible cable rails on the deck.

With its high ceilings and expanse of glass, the addition contains what some remodelers might call expensive air. But the project was budget-driven, and Alphin, who has a degree in architecture, took the lead in devising creative ways to build it without compromising the intent of the design or the quality of the construction. The budget started at $350,000 and ended in the “high 400s,” he says, due to “the combination of the scope increasing and the difference between what was allowed for in the schematic design and the final design.”

At one point, Alphin walked through the house with architect Susan Cannon. “They had fleshed out the design of the cabinetry,” he says, “and it was much more involved than the original schematics and therefore over the original budget.” He recalls Cannon making a comment to the effect that budget sometimes improves design because it forces you to simplify. “That was a process that was repeated over and over,” Alphin says.

For instance, where the original plan called for built-in cabinets made mainly of mahogany, “we pared it down to mostly Sheetrock openings with mahogany counters above white lacquer cabinets,” Alphin says. “The cabinets are still very functional, and the effect is still stunning, perhaps better.”

Similar compromises involved the windows and the fireplace. Rob Allen, an intern architect who did much of the legwork on the project, says one idea was to “mirror” the fireplace and bench outside, on the deck. The mirroring plan was abandoned for budgetary reasons, but Alphin's crew did such an artful job setting the fireplace and installing the steel chimney, which can be seen through the glass, that the effect is no less dramatic.

Designing and building the truss system proved to be the project's biggest challenge and its best opportunity to test Cannon's theory of better design through simplicity.

Water drainage is a major issue with butterfly roofs. To divert rainwater away from the house, a massive triangular cricket runs three-quarters the length of the house and narrows to a point at the back, where a 4-foot-long aluminum scupper shoots the water onto gravel-covered ground sloping away from the building. The cricket — nicknamed “the Mothra,” by Alphin's crew, in honor of an insect monster from Japanese B-movies — also prevents debris from accumulating in the valleys.

An even greater challenge was to make the roof structurally sound, says Richard Kaydos-Daniels, a structural engineer who played a vital role in the project. “We had to do some creative steel framing,” especially since the load-bearing walls have more glass than frame. Vertical support came from 4-inch-square steel columns that Alphin says were “absolutely essential” and are now concealed in the walls.

Rather than sheathing the two butterfly planes and then “over framing” the cricket, Alphin framed the planes and the cricket together, interlocking the butterfly framing and the cricket framing. Then the sheathing was installed. This framing not only added to the strength of the roof, but also created a little attic space.

The truss system itself was a response to the demands of the design. “It could have been done without trusses, with just inverted rafters, since we had the big steel beams,” Kaydos-Daniels says. But the rafters taper at the roofline, and “the thinness of the eaves condition dictated that we use a truss.” The braided cables — the only metal components that were not designed and fabricated locally — provide an elegant, tensile counterpoint to the wood rafters and steel rods.

“The truss was the real collaborative process,” Alphin says. The architects' original idea for a truss was “kind of vague,” so he, the architects, Kaydos-Daniels, and the steel fabricator who made almost all of the steel components spent considerable time evaluating different materials and structural issues as the project unfolded. A later design was “pretty elaborate,” and further collaboration led to the simplified final design.

With the design finessed, the construction of the roof began in earnest. The steel columns and beams were craned into place in one day. Working out of separate shops, and using full-size patterns to ensure accuracy, Alphin's crew assembled and pre-finished the wooden rafters, while the metal fabricator made the steel boots and other metal components.

The separate parts only actually came together on site. Allen remembers “a 98-degree day” on which the steel fabricator carried the boots up a ladder and welded them onto the I-beam. Alphin's team sprayed engine paint on the steel, and a couple of days later bolted the wood into position, each a perfect fit.

The metal deck and other roofing components followed shortly after, including 4-inch-thick structural insulated panels (SIPs) between the shingles and corrugated metal deck. Alphin's crew installed the cables, then winched them to the proper tension using a turnbuckle.

However unconventional the design and execution, this bungalow's butterfly roof works. “I would trust that roof against any other roof because of Will Alphin,” Kaydos-Daniels says.