Tuesday, February 24, 2009

Douglas Fir Timbers – a Good Choice!

Douglas fir is certainly one of the most popular wood choices for a post and beam or timber frame home because of its structural integrity and handsome appearance. Structural posts and timbers are graded according to the American Lumber Standard Committee, Inc. through accredited agencies such as the Western Wood Products Association’s (WWPA) lumber grading rules.

A structural timber’s strength is graded for strength or physical appearance. After a timber passes through a planer for surfacing, an inspector evaluates all four sides and the ends of the timber before assigning it a grade. The inspector looks at:

Wood characteristics: both natural growth and imperfections

Knots: checked for size, location, displacement, quality, and occurrence

Holes: (where knots have fallen out), for size and location

Wane: the presence of bark or the lack of wood fiber along the edge of the timber

Splits, Shakes, and Seasonal Checks: separations in the wood that can affect the structural integrity of the timber

Slope of the Grain: the deviation of the line of fibers from a straight line parallel to the sides of the timber

Warp: a bow, crook, twist, or cup in the timber

The way a timber is sawn is relative to its structural integrity. We recommend only “free of heart center” FOHC timbers, which means that the usual 'bulls eye' heart wood found in the center of most beams is absent. Free of heart timber also checks less and is more stable than timber which does have heart wood.

Consult with your timber frame architect on which wood species and grade is appropriate for your home!

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