Wooden decking boards are the most susceptible to shrinking and expanding. When exposed to moisture, they can easily absorb it and swell. When the boards dry out, it returns to its original size.

How much do deck boards shrink?

Installing Deck Boards During the Humid Months

So if you are using dry, untreated boards, you will have to install them with a slight gap of about 1/4 in (0.64 cm). This way, the boards will expand over the rest of the humid season and then shrink once the dry seasons arrive, leaving an appropriate gap.

Do deck boards shrink in length?

If the wood is put up dry, it might swell some in the rain, but will not dry much under 12% MC, so lengthwise shrinkage is minimal. Normal shrinkage is 0.1% for many species without juvenile or compression wood. Another factor, away from the juvenile core, which is 15 to 20 rings out from the center, are knots.