Structural Engineering: RE: Doug. Fir Lumber Grades

Thanks to Gerald and Dave for their input. Yes, I've gone through this before with panelized roofs and know the problems. I gues my new question is: To use the values for "No.1 and Better", would the piece of lumber have to be stamped as such? As far as I know, back in the '70's there was no such grade, so I imagine lumber of that era couldn't be designed as such. Do lumber pieces used today have a stamp that actually says "No. 1 and Better", if that is what is called for in the wood specs, or is it something like a mixture of No. 1 and Sel. Str.?

Thanks again,

Larry

Subject: RE: Doug. Fir Lumber Grades
Date: Fri, 26 Sep 2008 12:53:26 -0500
From: David.Gaines@hdrinc.com
To: seaint@seaint.org

Larry,

For a panelized roof system the owners and contractors probably did not use "No.1 and Better" grade of purlins and subpurlins. You may need to get up on a lift and find a few grade stamps to confirm the contractor used what was shown on the plans. Another way to confirm (E) lumber grading is to compare the actual size and position of knots to the WWPA or WCLIB lumber grading rules, but that requires a bit more skill and research.

Gerard has made a good point. You won't be able to make the (E) 1970's joists or purlins calc out for new loads using today's allowable stress values. You'll have to reinforce them or replace them for new loads. Check the beams and girders too. You may find elevated stress levels. Good luck.

Dave Gaines, P.E.

(626) 410-3631 cell
(626) 794-4117 home
(626) 584-4960 office direct line

gainesengr@earthlink.net

From: Larry Hauer [mailto:lhauer@live.com]
Sent: Friday, September 26, 2008 6:57 AM
To: Struct. Eng. Assoc.
Subject: Doug. Fir Lumber Grades

I am checking an existing "panelized" roof system, (cira 1970's), for the addition of equipment and screening on the roof. Ever since, I believe, the '94 UBC there have been stress values for doug. fir 2x and 4x for "No. 1" and "No. 1 and Better", and I have never understood when it is appropriate to use the "No. 1 and Better" values. Can anyone shed some light on this?

Thanks in advance,

Larry Hauer, S.E.

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