Decking:
There has been a long-standing debate over which side of a deck board should face up. Because boards have a tendency to cup, the cup side should face the ground so water will not stand on it. Which way will a board cup? This is where the debate is centered. Old growth lumber acted in a somewhat predictable manner. The decking available today is not cut from old growth trees and it doesn't act in a conventional manner. Here's the best advice. If the board is cupped put the cup down. If the board is flat put the best looking side up.
Working With Treated Lumber:
Pressure-treated lumber is commonly used to construct decks and other outside structures. Most people have little idea what the treatment is and how to handle "treated wood". CCA (cromated copper arsenate) is the most common chemical used to treat deck lumber. The waterborne chemical is forced deep into the wood fiber in a large pressure vessel. CCA inhibits mold, mildew and insect infestation. CCA gives treated wood its distinctive green hue. Manufactures claim CCA is relatively inert, but environmentalists have a slightly different opinion. Regardless of which side you take, it is a chemical and should be handled and used with some caution. When handling, wear gloves. When sawing, sanding, or drilling treated wood, wear a dust mask. When disposing of scraps, don't burn them--toxic fumes may be released. Always wash up before smoking or eating and when done working with CCA. Keep foodstuffs from direct contact with picnic tables built from treated lumber, and don't allow children to chew or lick the material.
Treated Lumber:
Treated lumber has become a common building material and is most often used for deck construction. Treated lumber is easily identified by its greenish tint: a result of the treating process. Not all treated lumber is intended for the same use. Chemicals used to treat the wood can be applied in different concentrations. The manufacturer's stamp on each board will identify its intended use: treated to .25 pcf for above ground use; .4 pcf for ground contact; and .6 pcf for burial or wood foundations. Treating wood makes it rot-resistant, not water-resistant. Applying water repellent will make an installation last longer and look nicer. Premium grades are dried after treatment, stamped KDAT, and may be worth the extra expense.