Grading of Lumber: Post And Beam Barns

Serious organic flaws in post and beam barns wood such as large knots at the edge of a timber can greatly diminish both shear and bending strength.

Other defects are checks (shrinkage gaps), splits, and shake (separation of annual growth layers.)

Shake weakens a timber considerably.

This is where lumber grading becomes important.

Trained lumber graders can certify a particular timber as being of a certain structural grade. However, the buyer must still be aware.

At a meeting of sawyers I attended in December of 2002, an example was shown of a graded two-by-four stud purchased from a large building supplier.

The grade stamp was clearly printed right on the stud. Because of poor quality in post and beam barns wood, it took little effort to break the two-by-four in half by hand.

The issue of using graded or non-graded lumber is a serious one and affects the owner-builder profoundly.

Listen: In early 2003, 48 of the 50 American states (including New York, where I live) have adopted the so-called International Building Code.

(I say so-called because I cannot imagine that this 3-pound volume of codes would be of much use outside of North America.)

One of the code requirements in this hefty volume is that all structural lumber be graded. Paragraph R$o2.i says, "Load-bearing dimension lumber for joists, beams and girders shall be identified by a grade mark of a lumber grading or inspection agency that has been approved by an accreditation body that complies with DOC PS 20.

In lieu of a grade mark, a certificate of inspection issued by a lumber grading or inspection agency meeting the requirements of this section shall be accepted."

Paragraph R6o2.i says the same thing with regard to "studs, plates and headers" and Paragraph R8O2.I includes "rafters, trusses and ceiling joists."

In short, all structural wooden components for post and beam barns in residential structures in 48 states must be graded.

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