Home is Built on Stilts

Just a short drive outside of Austin, Texas, the crystalline water and dramatic scenery of Lake Travis make it a popular destination. Despite frequent flooding, communities have developed around the 64-mile (103-km) lake. When architect David Webber, principal of Austin-based Webber + Studio Inc., received a call from a client who wanted to build a home in a low- lying neighborhood close to the waterfront, he rose to the challenge.

Actually a reservoir behind Mansfield Dam on the Colorado River, Lake Travis was constructed to contain floodwaters until they can be safely released downstream. New floodplain regulations mandate structures near the lake be built at the spillway height, so Webber knew his client’s 1,650-square-foot (153-m2) home would need to stand on 20-foot (6-m) stilts.

STRONG SOLUTION

Temperature differentials on the lake create harsh updrafts and because the water doesn’t move in one direction, strong winds come off the surface at varying angles. Webber + Studio’s staff had to design the structure to withstand these lateral forces high in the air. Although the designers considered cinderblock, cast-in-place concrete and wood, steel was the best choice to fit the project’s budget.

“The amount of strength you get from steel per pound and per dollar is extremely efficient,” Webber says. Steel also appeals to him for its environmental properties. “We try to select materials that are renewable and recyclable, and steel can be reused in a new capacity.”

Using steel in residential construction wasn’t a new idea for Webber’s firm, but the house on Hurst Hollow Road required a completely new strategy. Many of the neighborhood residences were typical suburban homes propped up on skinny legs to avoid the floods. Drawn to the industrial aesthetic of the area’s boat sheds, Webber decided to adapt the idea of warehouse building systems into a structure that would create a sense of openness appropriate to the lakefront.

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FRAMING THE VIEW

The Hurst Hollow house is designed with metal stilts that extend into rigid frames, forming columns on either side of the building and roof. On the north and east sides of the house, walls primarily composed of windows offer stunning lake views. The south side of the building includes an exterior switchback ramp for the resident, and Webber used this as a strong architectural form and incorporated it into the building’s arch. The house was designed asymmetrically, and the south-side columns became open buttresses surrounding the ramp.

A more complex, lighter metal frame between the main columns supports the roof, ceiling and floor. The frames are expressed on the interior, and the 2-story volume slopes up to 18-feet (5.4-m) high in the living room and dining area. Above the guest room, bathroom and laundry, the architects divided the space horizontally to provide a cozy bedroom with flexibility for a future balcony. Wrapped around the north and east sides of the home is 840 square feet (78 m2) of deck space looking out on Lake Travis.

According to Webber, a benefit of warehouse architecture is that the walls can go anywhere. Because the structural bays are the ordering system of a building, he opted to line up the walls with the major structural elements. The end walls align with the structural bays and the north and south walls maintain a relationship to the roof to provide visual clarity.

INNOVATION IN THE FIELD

During the steel-frame erection, the team hit a learning curve. Separate foundation footings were placed under each column, and the original proposal for the foundation connections was a lightweight epoxy connection that relied on having the entire frame braced off. Contractor Paul Balmuth, owner of Austin-based PB Construction, says the frame needed to be attached to something, so the team re-engineered the connections and decided to bolt weld plates onto the top of the concrete with expansion bolts. Concerned about the precise accuracy required for pre-drilled plates, the team elected to fillet-weld all the connections instead. Because the individual concrete piers could settle differently, each column was brought to the site 2 feet (0.6 m) longer than needed and cut down to precise dimensions in the field.

Connector bolts were intended to be installed, but the team decided the building would look cleaner without them. For Bret Smith, owner of Giddings, Texas-based Smith Welding, who fabricated, custom- welded and erected the home’s structural steel, this was a time-consuming process. A crane had to hold the frame in place while Smith’s team tack welded all the pieces together. The most difficult connections were the cross members for the roof because the beams were nearly 40 feet (12 m) in the air.

“This was not an out-of-the-box project,” Smith says, “so we had to respond to what was in front of us and invent ideas on the fly.”

The home has a Galvalume, Kynarfinished, standing-seam metal roof and metal siding. A special double roof helps prevent heat gain with two roof decks separated by a 3/4-inch (19-mm) air space above the insulation.

“It was an inexpensive solution that creates an effective thermal break between the roof and the home’s interior,” Balmuth explains.

Because the roof was part of the overall frame, it provided weather protection for the construction crew while they built the house. Once the steel frame was erected, the team installed corrugated metal decking as a continuous subfloor, poured concrete and then set back the frame for the interior walls. The large decks provided a platform for workers, avoiding the slow and costly process of working on scaffolding.

The residence was completed in December 2006 when the lake water was low. During the following spring, the water rose nearly 35 feet (10.6 m), exceeding Lake Travis’ full capacity by 10 feet (3 m). The Hurst Hollow house stayed dry. “The house makes use of old technol- ogy and applies it in an unusual format,” Webber says. “Although we chose steel to save money and time, it inspired us to take a high-end warehouse approach to the project and invent something com- pletely unique on the site.”