Before selecting a type of wood for your project, consider the climate it will be exposed to. A dry environment may require different wood than you would use in a wet environment. The durability or longevity factor should be another consideration. Is the structure temporary or are you building it to last? The cost of natural woods is directly related to their longevity in outdoor conditions.
Redwood and Cedars
Redwood with a deep rich color has a high resistance to insect activity and water penetration. Lighter grades of redwood may be fine for decking and handrails. The higher quality redwood should be used for furniture. Cedars, both western and eastern types, are excellent woods for outdoor projects. Western cedar typically has a full red color throughout. Eastern red cedar will have white sapwood along its edges. The sapwood will rot if not treated with sealant. In general, the more natural red color to the three types of woods, the higher the cost. Both types of cedar will gray out in full sunlight and will need to be treated with a penetrating oil to preserve color.
Grown in swamps and sometimes pulled from southern rivers, cypress is a wood that can withstand almost any environment. Cypress is a close-grained wood with a yellow to white surface. Extremely resistant to rot, the wood will turn to a dark shade of gray when exposed to rain and sunlight. The wood can be treated to retain some of its color, but most sealants will eventually allow the surface to gray out over time. The cost of cypress boards varies greatly depending on availability. Most cypress is collected when swamp waters are low enough to allow access for harvest. Old logs pulled from rivers are treated like exotic woods and can be extremely high priced. Cypress makes for excellent siding and exterior trim.
Pressure-treated and Composite Boards
Pressure-treated lumber is typically a yellow pine that has been pressure-treated with a preservative. This type of lumber is impregnated with toxins. Generally, this wood should only be used in ground contact and for framing members of an outdoor structure. It should not be used where the lumber can be in permanent contact with animals or humans.
Plastic composites have come into the outdoor wood marketplace. These are constructed from recycled materials and treated with sunlight inhibitors to reduce fading. Special fasteners typically must be used to secure this type of material to the framing, as normal nails or screws can damage the internal recycled materials. Most plastic composites come with a limited warranty from the manufacturer, and certain installation practices may have to be followed. Cost for pressure-treated lumber and plastic composites varies greatly, depending on the amount of shipping involved.
Dry Climates and Temporary Structures
The woods and composite materials mentioned above are all suitable for wet and dry environments. Oak hardwoods such as white oak, red oak and post oak can be used for decking and railing material in dry climates. The low humidity allows the wood to withstand softening due to rot. The tight grain of the wood can keep insects from penetrating the surface and causing damage. Termite infestation may become a problem if this wood is left in contact with the ground.
Inexpensive pine boards such as white pine and yellow pine can be used for temporary structures. Typically, untreated pine boards can withstand outdoor environments for two to three years. The soft wood can be used for chairs and tables if they are painted and brought under cover during cold and inclement weather.