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Re: Moisture Content in Timber

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This one is for all you wood experts:

The 1997 edition of the National Design Specifications, Section 4.1.4
appears to suggest a 19% moisture content as the expected service condition
for structural timber. However, the 1997 UBC Table 16-E footnote 1 says
"Seasoned lumber is lumber having a moisture content of less than 16% at the
time of installation...". If both these statements are accepted as
guidelines for design, then, does that mean that timber cannot be considered
seasoned when used for structural purposes?

This makes a considerable difference in the design of long spaned members.

Regardless of how structural lumber is specified for a project, much of the
structural lumber that is delivered to a construction site is delivered
"wet". Yet, these members can be expected to dry out over time - in fact,
much of the moisture content is lost even before the members are placed in
service. Also, members of relatively smaller cross-section would "air-dry"
more quickly than members of larger cross-section. Yet, I have not found
provisions that consider this fact.

Any comments on this issue would be appreciated.

-Richard L. Flower, P. E.



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