In Japan, the deck became an extension of the pavilion, often appearing to float out over a water body. Wood benches were incorporated into the framing and the orientation of the deck was directed towards specific views.
The use of the deck in Chinese and Japanese cultures often served the individual or family as a platform from which to view the garden, or as a place of contemplation.
This is in contrast to western cultures, in which the deck is focal point for entertaining and socializing, its size sometimes overwhelming the remainder of the garden. In suburban areas, where space is plentiful, decks have evolved into a rambling style, less formal than their prototypical urban porch or verandah.
Decks are also used to link the house to the outdoors on steeply sloped sites, where patios are not possible.
A Unique Construction Challenge
The framing of a deck is similar to the framing of a traditional house, designed as a load bearing structure. The major difference is that the deck framing must stand rigid without the stability of floor sheathing, continuous foundations, walls, or a roof.
A deck is typically built without solid sides or an impermeable covering above, and it is constantly exposed to the weathering effects of the climate, rain, snow, and temperature changes. Prolonged exposure to moisture promotes the growth of molds and fungi and results in unsafe slippery surfaces.
Safety is also an issue when the deck is raised above finish grade. Accidental falls over the edge are a concern, especially for younger children. Beyond safety, form and integration with other built or natural elements, level changes, site grades, entries, and traffic flow will all influence the design of the structure.
Two Structural Systems
There are two structural systems commonly employed in deck construction, platform framing and plank-and-beam framing. The difference between the two is relatively simple.
The platform framing utilizes an intermediary horizontal structural member, the joist, to transfer loads from the decking to the beam. The joists are typically spaced 16" to 24" (41 to 61 centimeters) apart and because of their size—2X6 or 2X8—allow for a greater distance between the beams below than in the plank-and-beam system. The thickness of the joist must be included in the finished profile, thus this system, produces a thicker substructure.
Plank-and-beam framing utilizes a single horizontal structural member, a beam, to transfer the loads from the deck to the post. Eliminating the joists allows for a lower profile, but plank-and-beam decking typically spans greater distances and requires a thicker material than that used in the platform method.
Basic Framing
When designing a structure, the process work is thought through, in reverse of the actual building process. The spacing of the members is determined by the span of the members above, thus a top-to-down sequence makes sense.
The process becomes somewhat circular as aesthetic decisions may require dimensional changes of the members and the necessary recalculations. The order in this description of decking follows the structure as it is built.
Next week we continue the five-part series with Part II: Decks, Fundamentals of Foundations.
Daniel Winterbottom teaches in the University of Washington's Department of Landscape Architecture. His interests focus on urban and community landscape design, vernacular landscapes, therapeutic gardens, sustainable design, and the craft and detailing of built forms. He is principal of Winterbottom Design, a Seattle-based landscape architecture and site planning firm.
Wood in the Landscape: A Practical Guide to Specification and Design, copyright 2000 by Daniel Winterbottom, is available at bookstores and at Amazon. To order from the publisher, visit John Wiley & Sons or call 800-225-5945.
Note: Photographs in the book are in black and white.
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