You have several choices when selecting lumber for outdoor projects. The type of lumber used depends on the project requirements for bearing weight, weathering and ground contact. Wood used in posts and fences, for example, is more susceptible to rot because it's in contact with the wet ground. Additionally, your budget may limit the type of lumber used.
Grades of Lumber
Lumber grades reflect the quality of the wood, such as the number of knots, amount of warping and other defects. Knots are weak places in the wood. The best lumber is grade No. 1, as it is stronger and straighter than the other grades. While you need that strength for weight-bearing projects such as building a deck, you can save money by purchasing a lesser grade for smaller projects, such as a planter for a rose bush.
Woodworkers prefer hardwood lumber for most outside projects. Hardwood trees have fibers that are denser and stronger than the fibers of softwood trees. Ironwoods, or "axe breakers," are the densest and heaviest of the hardwoods. Hardwood lumber is long lasting and naturally resistant to rot and infestation, in addition to being stronger. It is the most expensive lumber you can buy. Very heavy wood includes ebony, mountain mahogany, cherry, hickory, persimmon, canyon live oak, black locust and acacia. Heavy wood includes dogwood, pecan, teak, sugar maple, California black walnut, scarlet oak and Arizona ash.
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Some softwood trees are popular for backyard projects, such as deck chairs and planters. Softwood lumber is weaker and shorter-lived than hardwoods, yet some species are very expensive, including cedar and redwood. Other types of softwood lumber used outside include Ponderosa and sugar pines, spruce and white fir. This second group is among the cheapest lumber you can buy.
Pressure-treated lumber is the cheapest way to build your project. The mill infuses the lumber with chemicals that create superior resistance to rot. Pressure-treated lumber has a green tinge throughout the board and requires special care when cutting or handling it. You can stain the wood to hide the green tinge. The mills usually treat softwood lumber for rot, as its lower fiber density makes it more susceptible to the weather. Pressure-treated lumber may show the damage from the injection holes, so examine each board before purchase.