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Fire
Because wood is flammable, when used in the construction of buildings it poses a fire risk. Scientists studying the relative risks of different wood types look at factors such as the rate of ignition and the speed at which flames will spread along the wood. For example, the Forest Products Laboratory website lists yellow poplar, walnut, sweetgum, cottonwood, oak and yellow birch and maple as having the highest flame spread indexes for sawn boards.
Decay
All wood that is exposed to the elements should be treated with preservative to decay and insect infestation. According to the University of Tennessee, wood that is pressure treated will last longest. Alternatively, you can select wood based on its natural resistance to decay. Trees with highly decay-resistant wood include black locust, osage-orange, red mulberry and yews. Some of the least resistance species include alder, ash, maples, hickory, beech and birch.
Conductivity
Thermal conductivity refers to the wood's resistance to the flow of heat -- a particularly important property when considering the best choices for insulation. According to the Wood Web website, some of the least thermally conductive woods include northern white cedar, American basswood, balsam fir, redwood, and white and Engelmann spruce. Electrical conductivity refers to the wood's resistance to the flow of electricity and is important when choosing wood to support high voltage cables and for use in tools.
Moisture Content
The weight of water in a piece of wood is known as its moisture content and it determines the wood's strength, weight and potential for shrinkage. Commercially available wood with the highest moisture content includes bald cypress, American chestnut, cottonwood, white fir, hemlock, American Sycamore and Tupelo. The Wood Web website says that woods with low moisture content include white ash, rock elm, oak and cedar.