Wood in the Landscape: Decks Part IV
by Daniel Winterbottom
This article continues our five part series on deck construction. In this installment, we look at decking and stairs—installing decking to ensure its long life, bracing the structure, and constructing stringers and steps.
The decking provides a usable surface on which to stand and walk. It spans the joists or beams, transferring live weights to the structural members below. The span is determined by the spacing of the joists below and is calculated to the size and span capabilities of the decking material.
There are a number of options when specifying the decking material. Any material under 5/4 inch should be avoided for exposed decking applications. The material choices include 5/4 X 6, 2X4, or 2X6. The 5/4 or 2X material used for decking should be no greater than 6 inches in width due to a propensity to warp in wider boards.
In some public structures, thicker material (2 or 3 inches) is used in the plank-and-beam method, and as the thickness of the decking material increases, so too can the spacing of the joists or beams. A gap of 1/8 to 1/4 inch should be maintained between the decking boards, depending on their moisture content and subsequent shrinking, to allow proper drainage.
Because the decking, rails, and seating are the most visual elements of the deck structure, appearance-grade materials are often selected to build them. The "bark side" should face up so any cupping that occurs will not deflect water down, allowing proper drainage between the decking materials.
Decking is most frequently laid in flat with the thinnest dimension in the vertical orientation. However, as the spans increase it is possible to lay the decking in the vertical position and widen the beam or joist spacing.
This article is the fourth in a five-part series. It was excerpted from Wood in the Landscape: A Practical Guide to Specification and Design, with permission of the publisher, John Wiley & Sons,
All boards have a crown, a bow in the longitudinal direction. It should be oriented up, providing greater resistance to loads. If reversed, the member will tend to sag.
Image: Jody Estes
When the "bark side" is oriented down, the boards cup up, entrapping water. When it's oriented up, the boards will shed water and will tend to flatten over time.
Image: Jody Estes
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