Lagerquist & Morris AIA
5135 Ballard Ave NW Seattle, WA 98107Phone: (206)789-7611Fax: (206)
Strobel Houseboat
Exterior | Interior | Details | Construction

Floating Home With an Underwater Room

The owner retired, bought an old but nice houseboat on an inside moorage along Lake Union’s East shore. His intention was to remodel, add a second floor to gain a view of the city over his new neighbors, and settle in to enjoy the bohemian Lake Lifestyle. His program called for a two bedroom, two bath floating home with home office and a professional style kitchen. The site, on Lake Union’s east shore, is sunny, but tucked along the shore behind every other floating home on the dock. Views from the first floor are limited to the water (the main reason for being on the Lake), and up the channel to the open Lake. Kitchen- Dining-Entertaining were to be arranged on this level in a two-story space with access to a large water level deck. Overlooking this space would be the Living-TV-Entertaining space, which would look over neighbors to gain distant views of the City and the Lake. This level would access exterior decks for entertaining-viewing in good weather. Energy efficiency would be provided by a hydronic water to air heat pump, and cross ventilation would be provided by tilt-turn wood windows.

A Number of Existing Conditions Complicated The Owner’s Plans

First, the existing float was built with an extra layer of very tall stringers that raised the finished floor so high that a second story couldn’t be designed with legal ceiling height and remain under Lake Union’s 18’ limit. Secondly, the existing float touched bottom at the shoreward end, eliminating the possibility of adding additional floatation barrels, which the weight of the second floor addition would require, unless we risked underwater landslides by dredging the steep sub-aquatic bottom to beyond repose. This would have been ecologically unsound and illegal. We analyzed alternatives and started over. The Owner donated the nice old house to The Center for Wooden Boats, and we began the design of a new home with a concrete float.

The New Design Approach Including Breaking New Ground

The program was redeveloped to take advantage of having a concrete float. We added in-floor heat with a hydronic heat pump. Because of the superior floata- tion provided by the concrete barge, we were able to select heavy equipment and tile, build a steel moment frame to support a curved window wall, and locate heavy items without fear of unbalancing the floating structure. Because all the framing was now to be new, we could also provide electronic and communication wiring everywhere in the new walls. We were also able to reshape the footprint of the float, and develop a mooring site for the owner’s powerboat by configuring the water level deck to match the boat’s bow curve. Diagrams confirmed that the boat could maneuver forward into the slip and back out, rotate and motor forward to the open lake.

Unusual Site Problems

We plumbed the depth of the lake and determined the vertical dimensions we had to respect in designing the new barge. The profile of the lake bottom required the new barge bottom to have a shallow draft at its shoreward end, but the barge had to become progressively deeper amidships to support the weight of the new house. We repeated the shoreward sloping bottom on the hull’s outward end. This provided a deep center section with shallow ends, suggesting the possibility of a basement. “Why not!” We said. The ensuing design added an under-water room with aquarium style 30” portal for aquatic viewing, and freed up space on the main floor level by accommodating a fine wine cellar, a mechanical room for the hydronic water-to-water heat pump, chillers for the wine cellar, emergency bilge pumps, etc.

Now How Do We Build This?

Finding a Naval Engineer and a capable barge builder led us to Friday Harbor and Ladner, British Columbia. Getting a permit to build in Canada is a whole story itself. Floating the house down to Seattle, and moving it into its slip is another complex story about cooperation by all the neighbors in outboard floating homes who had to be cut loose and floated out into the lake to allow us to move into our slip. Moving in was an all day process of high anxiety for the people whose homes were floated out into the lake to allow the move. The day evolved into a dock wide party when tension changed to relief as the final floating homes were reconnected to their moorings.


The shingle clad structure, with curved “NuWave” Zinkalume metal roof supported by square tube steel trusses, is a modern expression of the traditional bow roofed floating cottages common on Lake Union in the early 20th Century. Locally built Douglas Fir tilt-turn windows and the two-story volume enclosed by a curved window-wall, stream light into the living areas. Second floor decks at four corners allow exterior entertaining and viewing of the working lake and its Independence Day Celebration. The exposed bar joist trusses provide a lightweight and visually open support for the roof and dormers. The house is finished with simple detailing, metal edges on GWB openings, and 1x4 base on bamboo and tile floors. Electricity use is very low because of the hydronic heating system’s use of the lake water as its energy source.