We’re trying to figure out what type of wood to use for an outdoor deck. Any advice?
As in many areas of sustainable design, there are no perfect answers here. If sustainable forestry practices are your primary concern, be sure the wood you use is Forest Stewardship Council certified. Many sellers make claims that the exotic hardwoods now being used for decking are sustainably harvested, but it's important to do your own research and check with the supplier. Our firm has used redwood, cedar, ipe, and mahogany: in many cases, these woods can now be sourced FSC certified.
We like the exotic hardwoods, like ipe, balau, and mahogany, because we find them to be more durable than redwood or cedar (durability is a key characteristic of sustainability). Also, because the wood is stronger, you can use a thinner board, usually 5/4 (1-inch finish thickness), and save wood. The transport distance of exotic woods is an environmental concern, but many experts say overseas container shipping is more efficient than cross-country transport.
Another eco-friendly option you may want to consider is a composite decking material like Trex. We have used Trex—in fact, I just used it on my own house. It is very sustainable, and so far it's proving to be quite durable. But it just does not have the look and feel of wood decking. Architect Marian Keeler provides a detailed overview of plastic lumber in this Ask A Pro article. Fine Home Building has also published a good article on the subject of synthetic decking.