Need a book? Engineering books recommendations...

Return to index: [Subject] [Thread] [Date] [Author]

Re: appearance grade doug fir

[Subject Prev][Subject Next][Thread Prev][Thread Next]
The wood should also be able to be graded for a structural grade.  Assuming that you are dealing with doing "timber framing" (whether traditional timber framing with traditional mortise and tenon joints or just heavy timber with metal connections), technically speaking, the structural grading needs to be done after the members have been cut from the raw timbers (timber grading is a function of the length of the member, unlike dimensional lumber (i.e. 2x, 4x)).  Thus, even if you got "select structural" timbers from the lumber yard, strictly speaking any heavy timber members should be regraded after they have been "fabricated", although that rarely happens to my knowledge...but it certainly can be done.  All you would need is to have a certified grader come in and visually grade the timbers/members.  Some heavy timber suppliers/timber framings have graders on staff.

I will further note that for timber framing, you typically don't see grade stamps on the wood.  After all, you are going to typically be leaving such timbers exposed and the owners don't typically like to see a nice, honkin' ink grade stamp "peeking" through the stain or oil on the wood members!  :-)  Thus, for heavy timber construction/timber framing, you tend to get the grades by way of a sheet of paper much like you would for steel grades (i.e. a mill report).

Last, if it is heavy timber/timber framing (i.e. large solid timber cross sections), then the owner should be prepared for checking and splitting and such.  The appearance grade only addresses things like knots and slope of grain, to my knowledge.  Those timbers are still gonna shrink and distort, likely resulting in checking and splitting.  This will be especially true if your project is on the inland side of the San Diego area (i.e. closer to the more nice dry desert climate with much lower relative humidity).  If the timbers are a high appearance grade, then that should mean you will have little to no knots and rather nice straight grain, so there should be less distortion/warping, but you will almost definitely, if not definitely, still get splitting and checking.  If you want it to be a bit more predictable (i.e. generally see the splitting and checking before installation), then specify kiln dried timbers...but that may not completely prevent future movement issues and splitting/checking.  The point is the with solid lumber it is generally VERY hard to get perfectly clean will almost definitely, if not definitely, get checks and splits at least.  If you want to avoid such shrinkage issues, then go with glulams...of course, the owner will have to be willing to over look the glue lines/visible laminations.



On Apr 8, 2011, at 11:42 AM, karen roberts wrote:

I have a client who wants to use an appearance grade DF lumber for framing the roof of his room addition as it will be exposed from the underside and he is going for a very clean aesthetic.  I cannot seem to find anything definitive about the structural integrity for appearance grade wood.  I would presume that a clear grade would actually be stronger than even a no. 1, maybe even better than a select structural because it has fewer inperfections and is generally from older growth wood, but does anyone know if I could reasonably estimate the structural capacity of this wood?  Are there possibly other issues that I am overlooking with the structural capacity of appearance grade wood?  We are the designers and builders of this project and I don't want there to be any issues with the design, nor any problems in plan review or during inspections (grade stamp on the lumber).
thank you for any thoughts or opinions.
San Diego, CA