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RE: Wood Difference

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The one thing that I would modify is that not all timber sizes are always specified in nominal dimensions.  Some are specified in net dimensions (aka "real" dimensions).  You can see this often in the timber framing industry.  Of course, those dimensions might be when they are green timbers, so the real dimensions for in use after the timbers have reached an equilibrium moisture content in use will typically be smaller due to shrinkage.
 
And while I am no grading expert (I know enough to be dangerous), you are correct in that timbers technically must be re-graded if their length is modified.  This is due to the grading being a function of the number of knots within particular section of length...if the overall length of that member changes, then that reference length can change as well.  I don't believe that is true of lumber material (i.e. 2xs) if I recall correctly.
 
As to "naming", technically in the NDS, typical stick framing is "dimesion lumber", which is lumber that is 2" to 4" thick (nominal) and 2" (nominal) or more in width.  Then, there is "beams and stringer" lumber and "posts and timber" lumber...both of which are commonly referred to as "timbers"...both of which are 5" in each dimension or greater, but with "beams and stringers" being at least 2" wider than they are thick and "posts and timbers" being less than 2" wider than thick (i.e. "beams & stringers" are more rectangular" while "posts and timbers" are more square).  But, officially, the NDS refers to it all as lumber.  But, the common terminology is lumber for the "stick" stuff and timber for the "beefy" stuff.
 
Regards,
 
Scott
Adrian, MI
-----Original Message-----
From: Jordan Truesdell, PE [mailto:seaint2(--nospam--at)truesdellengineering.com]
Sent: Thursday, June 26, 2008 9:33 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: Wood Difference

In an engineering sense here in the states, a timber is any member with the smaller side equal to or greater than 5" (nominal); lumber is anything smaller. I.e. 2x12s are lumber; 4x6s are lumber, 6x6s are timber, as are 6x12s and 16x28s. Nominal sizes for lumber are 1/2" less for widths up to 6", and 3/4" less than nominal for widths above 6". Timber sizes are all 1/2" less than nominal.

More specifically, the timber engineering values are noticeably lower for a given species and grade than their lumber equivalents.  I believe that timbers are also graded as cut lengths. A 10 foot long 2x6 No.2 may be cut to any length and still be a No. 2 grade, but a 14' long 8x14 No. 2 timber which cut to 8' long must be re-graded.  Buddy or Scott may chime in here and tell me if I'm correct or not, as I don't have a reference other than the odd conversation with forgotten sources.

Clear as mud.
Jordan


Rhkratzse(--nospam--at)aol.com wrote:
Dam little.  Wood is a very general term for the "meat" of a tree, down to toothpicks or chopsticks.  Lumber is after it's been sawn into pieces and generally means pieces used for building (as opposed to eating or picking one's teeth).  Timber is a term generally used to describe larger pieces of lumber, but may vary and isn't very specific.

HTH,

Ralph

In a message dated 6/26/08 10:11:28 AM, jjtreff(--nospam--at)hotmail.com writes:
For most of you this might be a very basic question, but for someone coming from a country where only masonry and concrete exist, it's confusing.

Structurally speaking, what's the difference between wood, lumber and timber?

Thank you!



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