As stated above, pressure treated lumber is the dominate decking product in the market. Relatively low cost, excellent strength & workability characteristics, and wide availability are responsible for its popularity. Even if you select another decking material you will almost certainly still have pressure treated lumber used in your deck for all or most of the structural members. Alternative materials are either inadequate or too expensive for structural purposes.

Several waterborne preservatives are commonly used for preservation including Chromated Copper Arsenate (CCA), Alkaline Copper Quat (ACQ), Copper Azole (CA) and Sodium Borate (SBX). As of December 31, 2003 CCA has been withdrawn for most residential consumer treated lumber applications. (See: http://www.backyardamerica.com/cca.htm ). Copper is the primary fungicide in these preservatives. The preservatives are forced into the wood fibers under pressure in large chambers. Southern pine is the lumber species most commonly used for pressure treated decking and framing in the eastern part of the country because its cell structure allows adequate preservative penetration without incising the lumber.

Incising is the perforation of the lumber surface with small slits which allow the preservative to penetrate. It is required for most western softwood species. Pressure treated hem-fir is the most commonly used. Hem-fir actually refers to several western softwoods including Douglas fir, western hemlock,  red fir, silver fir, and white fir. The decking is often pre-stained for a cedar like appearance. When cut or drilled a preservative must be applied to the newly exposed surface to prevent rot.

Advantages

• Relatively low cost
• Widely available
• Long life (Many brands offer a lifetime warranty)
• Excellent structural values
• Very good for stains, OK for paint
• Easy to work, no special tools required
• Available in 5/4" and 2" decking and many other dimensions, as well as plywood and lattice.
• Wide selection of visible and hidden fasteners are available.

Disadvantages

• Weathers without cleaning and periodic application of stain/sealer.
• Splinters and "weather checks" are common
• Shrinks significantly unless kiln dried after treatment (KDAT).
• Requires more care in fastening and joints to reduce cupping and warping.