In a message dated 6/2/99 9:05:57 PM Pacific Daylight Time,
Southern Pine grading rules state that Kiln Dry is 15 percent moisture.
WWPA grading rules (1991) states that "Moisture is removed from lumber
by air drying or by use of special drying kilns." [Section 4.00, WWPA
Grading Rules] I think that this is the only place in the rules that "kiln"
is mentioned --- it certainly isn't in the glossary.
Section 4.10 states, "... Except as otherwise provided, any lumber surfaced
at a moisture content of 15% or less *MAY* be stamped 'MC 15'." [Emphasis
Supplement No. 3 to the WWPA grading rules gives the following definition:
"Kiln-Dried (KD) lumber is lumber that has been seasoned in a chamber to a
predetermined moisture content by applying heat."
It doesn't say what that "predetermined" moisture content should be. By the
definition, it could be 25 percent, if the lumber originally had 27 percent
PS20-94 has the same definition for "Kiln-dried" lumber that WWPA has.
So, the only assurance that we have that lumber had been surfaced at less
than 19 percent moisture would be if it had an "MC 15" stamp on it or was
graded as kiln dried Southern Pine under the SPIB grading rules. But even
then, the moisture content of the lumber may change as WWPA permits:
"Restrictions on moisture content shall apply at time of shipping as well as
at time of surfacing, except that when lumber is shipped in open
unprotected from the weather during transit, the seller is relieved of the
moisture restriction if the buyer is notified and consents to the method of
Since lumber degrades (and becomes less valuable) as it dries, you can bet
that most lumber is going to be graded at the moisture content it has at the
time that it is surfaced.
I have seen lumber in covered storage in lumber yards here in Tucson that
literally had moisture running out of it.
In addition, 5% of a shipment (1 of every 20 pieces) may actually be below
the grade stamped on it.
These are also part of the reasons that I am opposed to LRFD for wood
Hope this helps.
A. Roger Turk, P.E.(Structural)
Tucson, Arizona >>