Paul Fisette responds:
Depending on the wood type, moisture
content, and exposure, deck
boards can cup, twist, or decay. Theoretically,
you can ensure that a
board will cup downward to shed
water, and thereby reduce deterioration,
by exposing one face or the
other. In fact, seldom does a week
pass that I'm not involved in a discussion
about whether to install
deck boards either bark side up or
bark side down. But such recommendations
usually only account for
one of a handful of factors that control
cupping.
Original moisture content. The
original moisture content of a piece
of lumber controls a board's final
shape. Wood is stable when its moisture
content is above 30% (fiber saturation
point). As wood dries below
30%,