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Re: Moisture Content in Timber

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Richard

The key word in the paragraph is maximum. The maximum moisture content for
lumber (dimensional sizes 2 to 4 inches thick, and 2 to 12 inches wide) is
19% at time of manufacture, unless you specify 15% or Kiln Dried. The
average mc is more like 15%. You are correct in that most lumber dries in
transit to the lumber yard and then on to the job site. In most completed
structures, the "equilibrium" moisture content is from 6% to 12%. This is
considered seasoned.

In some cases, you may get "green" lumber. I hear that that happens in
California due to the large demand. Also, "timber" (5 x5 and larger) are
seldom available as seasoned, but are green (20% and higher MC.)

The section 4.1.4 is to define dry  service conditions and wet use service
conditions and when to apply wet service factors.


Bruce Pooley
Timber Design

----- Original Message -----
From: Richard Flower <RLFlower(--nospam--at)worldnet.att.net>
To: <seaint(--nospam--at)seaint.org>
Sent: Tuesday, July 18, 2000 9:04 AM
Subject: Re: Moisture Content in Timber


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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