Calculating longitudinal shrinkage

by Professor Gene Wengert

Q.
What factor should we use for calculating longitudinal shrinkage in hard maple strip flooring?

A.
I do not have any good ideas other than to use the traditional number of 0.2% (green to dry) which amounts to about 2-1/2 inches per 100 feet. However, since the shrinkage change occurs over a 30% MC change, then we could also say that the wood will shrink longitudinally about 0.1 inches per 1% MC change per 100 feet.

The problem comes when we consider the cross grain in the wood, plus any juvenile wood, all which can shrink up to 30 times more lengthwise. I haven’t seen much discussion of this lengthwise shrinkage.

Professor Gene Wengert is Extension Specialist in Wood Processing at the Department of Forestry, University of Wisconsin-Madison.

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Comment from contributor A:
The Canadian Wood Council "Introduction to Wood Design" seems to indicate a regular shrinkage coefficient of .002 and a longitudnal coefficient of .0005. p 5-17 c 1996