Next to the age old debate "Tastes Great" vs. "Less Filling", the debate about whether deck boards should be placed "Bark Side Up" (growth rings curving down) or "Bark Side Down" (growth rings curving up) has raged for years.
Bottom Line: I don't buy the hype that "bark side up" is always the answer and I'll tell you why. Then you can decide which way you want to install the boards.
Boards typically come in three cuts:
- Heart - Center of the growth rings are in the center of the board edge and is not too common because these are dimensionally prime pieces of lumber
- Edge Grain - Common, and
- Flat Grain - Most common
The issue of which way to orient the deck board is only relevant with Flat Grain boards because the orientation of their growth rings will affect how the wood reacts when wet. And in the case of a deck board, whether you have a "cup" warp or a "crown" warp.
Why Boards Warp: When deck boards get wet they do not get wet consistently. That is, the wood exposed to the rain and the wood on the bottom of the board are not being exposed to the same moisture. As a result, the wood fibers on the weathered or exposure side expand more than the fibers on the bottom. That creates dimensional changes in the wood. Wood warps the opposite orientation of the growth rings. The orientation of growth rings and which side gets wetter determines the way the wood warps on your deck.