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Modern House Features Tsunami Resiliency

By Kevin Wilcox

When flood zone maps were redrawn, a simple remodeling project in Puget Sound shifted into the creation of a modern beach house designed to endure.


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The structure is on a tight site, close to the water’s edge, and was designed to maximize the dramatic views of the water. Lucas Henning Photographic

February 4, 2014—A small beach house built on Camano Island in Washington's Puget Sound has drawn widespread attention recently by putting an elegant, modernist face on the pressing issue of tsunami resiliency. The house is designed to comfortably accommodate waves more than 7 ft tall without significant damage and is being viewed as a blueprint for the many structures that will need to withstand higher seas and stronger winds as climate change proceeds.

Yet if the project had gone according to its original plan, it would have never been built.

The graceful structure is the work of Designs Northwest Architect, of Stanwood, Washington. When the firm was first approached about the project, the scope was quite different, recalls Daniel Nelson, AIA, a principal of the firm. "There was an existing house on this site," Nelson says of the small waterfront cabin dating to the 1940s. And although the cabin needed repairs and renovation, it held great sentimental value to the owners, who wanted it preserved. Well into designing renovations to the cabin, the design team learned that new flood maps produced by the Federal Emergency Management Agency (FEMA) placed the property in a Zone V, meaning there was the potential for not only flooding, but tall waves.

Puget Sound is laced with earthquake faults and fault zones and is also vulnerable to movement of the Cascadia subduction zone. Additionally, historical records indicate that tsunamis have been created by large-scale collapses of tall island cliffs that have eroded over time. Nelson estimates that 40 percent of his firm's business involves projects within FEMA's Zone A, which is marked by slowly rising water from strong storms. This was their first Zone V project.  

"When we first started the house, the building department didn't even know themselves how high we had to go in this redesignation. So we actually hired the U.S. Army Corp of Engineers to do the calculations," Nelson says. The calculations indicated the waves might reach a height of 7 ft 8 in.

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Overhead glass doors on the cabana level can be opened to provide direct access to the shore. The walls were designed to resist 85 mph winds, but will break away—leaving the structure above still standing—when hit by a strong wave of water. Lucas Henning Photographic

"So, all of the sudden, we went from remodeling an existing cabin that was built in the 1940s to having to now raise this old cabin up 8 feet in the air and put a pier foundation underneath it," Nelson recalls. "When that happened, it didn't make sense to save the cabin. And so it turned into a new structure."

The new structure employs a robust series of 18 in by 18 in. concrete piers, anchored into a 1.6 ft thick mat foundation on the island's sandy soils. The columns are connected above by a series of thick concrete beams. "We created this ribbed box of concrete as the foundation for the house," Nelson says. The structure also had to be designed to withstand 85 mph winds. 

"There were many unique structural engineering problems associated with this project, which like many structural engineering challenges, resulted simply [from] the location of the structure," said Jason Lindquist, P.E., S.E., who was the engineer of record on the project for the firm West Coast Engineering, of Mukilteo, Washington, at the time. Lindquist, who is now the president of Equilibria Structural Engineering in Mukilteo, wrote in response to questions posed by Civil Engineering online.

"The poor soil conditions required ... the use of a raft foundation. Acting as a large distribution pad, the column forces were transferred into the supporting soils via the rigid foundation footing," Lindquist said. The selection of a raft rather than a deep pile system was also driven by the difficulty of installing deep pile systems at this location, he said.

"Since the owners wanted somewhat useable space below their house, any walls that were to be installed [had to be] be strong enough to withstand the high wind pressures without failing, yet weak enough to simply break away during a wave event," recalled Lindquist. "It's not often an engineer must design a connection to be weaker than a design force, and it went against everything I learned during my days in the University of Washington's [civil engineering] program." 

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The structure is founded on a 1.6 ft thick mat foundation atop the island’s sandy soils. Concrete piers elevate the house and are connected above by concrete columns. Lucas Henning Photographic

To accomplish this, the team specified aluminum panels that are attached by steel connectors to the concrete columns via plastic screws, Nelson says. These walls form a cabana area, accessible by way of the structure's large overhead glass doors.

Another engineering challenge resulted from the owners' request to maximize the dramatic views, Lindquist said. "To preserve the tremendous view of the ocean and to utilize the footprint to provide as much living space as possible, there [were] not enough walls to use conventional wood-framed shear walls for all of the lateral force-resisting systems," Lindquist said. "We used two steel moment frames to laterally support the structure and to provide an open, beachside feel to the house."

The glass overhead doors—transparent on the beach side and opaque, for privacy, on the street side—provide an open feel on the extremely tight site.

"The entire site was 3,100 square feet …and the site was 50 feet from the bulkhead to the road," Nelson explains. "We had to design a drain field on the site, and then design the house to meet the tsunami criteria for the V zone, and then fit everything on the site and make [it] livable. That's where we came up with the idea of the overhead doors. You can open up and let people flow through, giving a sense of great space on that lower level."

The 887 sq ft house has generated a great deal of media coverage. Nelson has fielded calls from media as far away as Europe and homeowners in Massachusetts and New Jersey who recently found out their properties are now in Zone V flood plains.

"With rising waters, storm surges, and the hurricanes that seem to be happening, these types of structures are going to become more prevalent," Nelson notes.

And what of the owners who originally wanted to preserve their cabin? Nelson recalls that when he learned of the new flood zone requirements, his first thought was, "What am I going to tell the client?" 

But the new home design won them over. "They love it," Nelson says. They recently told him the cabin provides a wonderful place for four generations of their family to gather together.

"It all worked out great in the end," Nelson says. "I tell [all of] my clients, the first thing I have to do is solve the problem. We have to figure out what we can do. And then we have to look at the soil conditions and solve the problem of how somebody is going to live in the structure. And then we have to solve the technical problems—in this case the V zone criteria.

"The look and the feel and the character of the house evolve from working with the client and the aesthetics that meet their needs," Nelson says.


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