Choosing a species of wood that is intrinsically resistant to rot is the first step to successful outdoor building projects. Heartwood is superior and resistant to rot because of natural preservatives stored in the heartwood. Some heartwoods that are very resistant to rot are redwood, cedar, black locust, Pacific yew and Osage orange. The outer wood of a tree, called sapwood, is not rot-resistant. Sapwood and softwood such as pine, ash and alder should be pressure-treated with a wood preservative for outdoor use.
Outdoor warped or rotted stair treads are a serious safety issue, leaving your family and visitors vulnerable to injury and you, as a homeowner, open to the possibility of a lawsuit. Homeowners insurance will not pay for injury caused by neglect or bad construction practices. Warped steps may be caused by poor selection of materials, lack of maintenance or poor surface treatments. The best wood for outdoor use is dimensionally stable and water repellent.
Type and Species of Wood
Dimensionally Stable Wood
The actual dimension of wood will change as wood begins to dry. Wood that is green, moist and unseasoned has high moisture content and will shrink as it ages and dries. To ensure minimum shrinkage and warping problems, wood should be dry before it's used. Select wood that has been kiln dried or left to air-dry naturally. Dried wood is dimensionally stable and resistant to rot and insects.
Water is the enemy of outdoor wood structures. Wood soaked with water swells, warps and, if left wet for long periods, molds and rots. Wood must be treated and maintained to make it impervious to water. Treatments include factory-applied preservatives, wood preservatives applied by the homeowner, paint and heavy body stains. If preservative or paint is not regularly applied as part of maintenance, the preservative will leach out and the paint will peel, leaving the wood vulnerable to water damage and warping.
Examine Your Lumber
When choosing lumber for any use, examine the board from all dimensions. Hold one end of the board at eye level and look down the length of the board. Look for twists, bows or arcs in the wood. Turn it flat and turn it on its side when sighting a board. Look for cracks, splits, knots and other defects. Choose lumber that is flat, straight and without defect.
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