Cedar Decking
Considered a soft wood, cedar has been used for decking for generations. Its natural resistance to rot and insects makes it desirable, however, it might to be too soft for decking and has a tendency to splinter, according to Gordon Whittaker. It's best used for vertical elements like the balustrade of the railing, privacy fencing or for structures like pergolas and planters. Again,the Rainforest Relief organization would argue that old-growth cedars of 100 to 250 years old, where the choicest cuts come from, are in danger of being destroyed forever.
Pressure-Treated Lumber
Pressure-treated lumber is rot and insect resistant, but it's cheaper than redwood or cedar and is widely available across the U.S. Deck builders use it to build the support systems for decks because it holds up well and is often masked by the deck flooring.
The problem with this type of wood is that it can be unstable, especially at lower prices. Shrinking, warping and twisting are all common with lesser-grade woods. If possible, pay a premium for higher-grade lumber that is treated at the mill with water repellents and sometimes pre-stained.
