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Lumber grades for analysis
2

Lumber grades for analysis

Lumber grades for analysis

(OP)
Which of the lumber grades, on, e.g., http://euler9.tripod.com under "Lumber Mechanical Properties," "Table 1," "2 x 6 inch," would be used for the rafters of a typical moderate or low-priced house or inexpensive wood-frame small commercial building? All pine lumber I see at stores such as Home Depot appears to be grade 3, I assume, even though it's unmarked and has few knots. The best pine lumber even at typical professional lumber yards is designated grade 3, I believe, even if it appears to have virtually no knots in most pieces. Which one of the grade delineations (rows) listed in the above web page table, for 2 x 6 inch, would be most likely for the described rafters in the described, typical construction most of the time?

The same question goes for the joists (and the same question goes for the studs in the typical stud walls supporting the roof, if you have time). Anything you can tell me about (or to define) the many grade name delineations listed on the above web page, as they relate to the real world and typical low-budget or subdivision project housing construction most of the time, would be greatly appreciated. I assume the strength values listed on the above web page include a factor of safety. If so, what factor of safety would you guess is built into those strength values? I couldn't find it yet on that web page nor in NDS for Wood Construction manual. Thanks.

RE: Lumber grades for analysis

According to Breyer ("Design of Wood Structures," 2nd Ed., page 126 - an INDESPENSIBLE textbook) "...[t]he combined effect of the adjustments [allowable stresses developed based on ASTM D245 and D2555, et al] is to provide and average factor of safety on the order of 2.5. [re.: values in the NDS.]"

Lumber for houses is a good question. Austrian spruce is really nice... A good resource is the Southern Pine Council's web site: http://www.southernpine.com/. They even list manufacturers.

My take on Home Depot lumber: beware of moisture content. Assume you will have noticable shrinkage within a couple of months.

RE: Lumber grades for analysis

2
Most codes require that primary members (top/bottom chords in trusses, or rafters/joists) be No. 2 or better.  Secondary members (diagonals, blocking, etc.) may be No. 3.

Check Southern Pine Inspection Bureau (SPIB) grading rules.

RE: Lumber grades for analysis

A real lumber yard should have No. 2 lumber no problem.  No. 3 lumber is typically used for non-load bearing partition walls.  Like DaveViking said, beware of Home Depot lumber.  Even if it says kiln dried, it's probably been sitting in the lumber yard for some time to absorb that moisture back.  I've pulled lumber of the stack and have seen standing water on the boards below.  Almost as if they bundled the wood in a torrential downpour.

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