I've been told that decking boards should always be installed "bark side up" so that the boards crown (and shed water) as they age rather than cup (and collect water). But then I've also heard that it should be done the other way around. And I've also heard that it just doesn't matter one way or the other - just put the "nicest" side up.
So, which way is best, or doesn't it matter at all?
I would say crown side up and shed water. The deck that was on my house when I bought it was cup side up and is in horrible shape. That could be from the fact that the people never took care of it but being in a rather wet/snowy climate didn't help. I'm sure pooled water of any kind can't be good, even on treated wood.
Although both ways are advised by different sources, I have built dozens of decks in Maine as a contractor and have found that pressure treated and cedar boards almost always crown to the bark side and recommend the bark side face outward. Obviously this helps shed water and doesn't collect ice in pockets in the winter. Don't mix the methods as this can result in a very unattractive surface after a couple of years. Always be sure to use treaded fasteners, never galvanized common nails and be sure to sink coated screws or stainless steel ring shank nails. make them flush or slightly below the wood surface to eliminate tripping hazards or use under deck clip systems. If you find some boards that have a bad finish on the side you want to expose, don't use them! Bring them back and have them replaced. This may sound like a pain, but flawed wood with checks or cracks will degrade very quickly and ruin all the hard work you have done on that expensive deck. Don't forget to water isolate the ledger from the building and resist the temptation to use cheap waterproofing products. Often the details of construction in areas you can't see is as if not more important than the viewed surfaces. Good luck.
Crown side down though helps prevent the boards from warping as much because the frame stops it from warping. Its easier for it to pull out the nails then it is to push through the frame
My son and our scout troop did a gazebo just before he turned 18 he is now 35. Some buddies and I have a prayer group down there when the weather is nice. I look at those boards, the smile is down with a screw and two galvanized nails at each joint. that deck is very flat. I am working on a deck now. I cut a top hand rail out of a plank and left it to put up later. We have had lots of rain here in KY so it was awhile before I got back to it. When I did the board had a small cup going with the direction of the "smile" of growth rings not against it. My guess is that wood growth rings change in relation to weather as against if wood is dried for indoor use. On my own deck I put the "smiles" down 5 years ago and the deck has remained basically flat and level. So I'm going with bark side up otherwise known as smile down. Treated or untreated may also make a difference. I noticed that Tommy Mac says smiles up but he was using dried and untreated mahogany. I maybe check to see what is working in your area with the type of wood and normal weather conditions. Ky has no normal weather conditions! I've read that Technically dried wood cups opposite direction of growth rings and that is the reason for bread board ends. Truthfully I have not noticed that. I'll take a look at the wood in my shop and let you all know.
