Selecting Wood for Outdoor Structures
Description/Purpose: Once an outdoor structure has the proper footings (see Deck and Outdoor Structure Footings), decisions need to be made as to appropriate materials to use in constructing its above ground portions. Examination of the six basic materials commonly used for outdoor structure will make these decisions easier.
Lower grade redwood is fine for decking and rails. Avoid wood that has light-colored sapwood. This wood is often not rot-resistant. For posts, it is best to use construction-heart or clear-heart grades. There is a direct relation between cost, and quality and durability of the grade of wood, the more costly higher grades being more durable. For more information on redwood and to view examples of structures using redwood visit the California Redwood Association's web page at www.calredwood.org/homeown/perfdeck/perfdec.htm and www.calredwood.org/ref/lit.htm, or Pacific Lumber Company at www.palco.com
Quality redwood will have a deep red color to it, which it is named after. In order to keep this rich color the wood must be treated with a clear wood finish or with a redwood stain. If the wood is left unstained, the color of the wood will turn to silver-gray.
High-grade heartwood is impervious to rot and insect damage. Lesser grades are more prone to rot and insect damage. To extend the life of the wood and to retain its original color, apply a penetrating oil sealer or stain.
Redwood can be used for all parts of a deck. However, due to its high cost you may only want to use it on the most visible parts of the deck. Redwood is most often used for decking and railings. It is relatively soft wood, and can be easily damaged, thus washers should be used for framing. When using fastening nails near the end of boards, it is best to drill holes to avoid splitting the wood.
Redwood is the most expensive wood used in decking and other structures. The farther away one is from the West Coast, the higher the prices will be. Redwood can be up to four times more expensive than pressure treated lumber.
Western red cedar can be readily found in premium, common, and construction grade wood. Avoid sapwood or streaky surfaced lumber as it is weak and may be blemished. For more information on cedar decking, railing and fencing go to House of Cedar at www.houseofcedar.com/lumber2.html.
Cedar is often a golden-brown color. When left untreated cedar will turn a grayish tone. Use a clear wood finish if you wish to preserve cedar's natural color.
Cedar is similar to redwood in its durability, and resistance to rot and insect pests.
Cedar is usually not used as a structural component in construction for it is much weaker than redwood, cypress, and pressure treated lumber. Cedar is used only for the decorative portions of a project.
On average cedar is about half the cost of redwood and about twice the cost of pressure treated lumber.
- Cypress Southern Cypress (also called bald cypress) is found in common and premium grades. Cypress is readily available in the Southeastern U.S., but may need to be ordered in other regions of the country.
Cypress is a tan to reddish color. The color is somewhat lighter than redwood.
Cypress is equal to redwood in its resistance to rot and insects.
Cypress can be used for both structural and ornamental purposes. Because of its high cost, many people use cypress only on highly visible areas of a deck or structure. Cypress is known for its tendency to twist and warp if not dried properly. However, it can be nailed or screwed down like redwood and does not need to be pre-drilled.
Cypress is affordable if you live near the Southeast. The farther away you are from the Southeast the more expensive it is. Depending on your region, cypress can be more expensive then redwood.
- Pressure-Treated Wood
Pressure-treated wood is made mostly of southern yellow pine, and occasionally fir. The wood is treated with chromated copper arsenate (CCA). CCA is an insecticide-preservative. PT, or pressure-treated lumber, may also be treated with water repellant. Arsenate is not as commonly used as a lumber preservative now as it once was. However, because of its toxicity to humans and animals, it is advisable to find out the type of preservative before purchasing the lumber. Less toxic chemically treated lumber is now available that does not contain arsenate.
Quality grades run in descending order and should be used for different purposes. Grade No. 1 is used for railings and benches. Grade No. 2 or better is used for decking. Check to see if the pressure-treated lumber is kiln dried. Kiln dried wood is more dimensionally stable than air-dried wood. Look for a KDAT stamp to ensure the wood you are using is kiln dried. For more information on pressure-treated wood see Building Products Plus at www.bp-plus.com.
Pressure treated lumber is a greenish color that will turn gray over time. This lumber has a more pronounced grain than redwood, cedar or cypress and will accept any exterior stain.
Pressure treated lumber is as durable and resistant to rot and insects as the previously discussed woods due to its chemical treatment.
This lumber can be used to build the entire deck, or it can be used just for the structural portions. Natural woods, such as cedar or redwood, can be used for the more visible parts of the deck. Pressure-treated lumber must be dried before use. Lumber of this type must also be sealed with a water repellant sealer unless previously treated.
Pressure treated lumber is by far the least expensive lumber to use on a deck or outdoor structure. Lumber of this type is generally half the price of redwood, cedar, and cypress.
Pressure-treated lumber has become an environmental concern over the last ten years. There are documented cases of people becoming ill while working with this lumber. Always wear gloves and a dust mask when working with this lumber.
- Tropical Hardwood
Tropical hardwood is becoming more abundant and is utilized more in the construction market today. Lumber sold as Ironwood or Pau Lope is twice as strong as oak and is more durable than redwood and cedar. These hardwoods have a life expectancy of 40 years or more and are resistant to insects and decay. All grades have very few knots and a tight grain pattern.
Tropical hardwood is very expensive and needs to be predrilled for fasteners. Tropical hardwood lumber can be found in all sizes and can be used for all parts of a deck, but its cost and slow delivery has restricted its use to deck surfaces and railings. There is also an ecological concern as to the harvesting of tropical hardwoods that may influence its use.
- Plastic-Wood Composites & Vinyl
Both of these materials are new materials that are becoming popular in the construction industry. Plastic-wood composite lumber is manufactured from a blend of 30 to 50 percent recycled plastic and wood fibers. For more information on this product see Trex at www.trex.com/TREX_SITE_1998/TrexECDPage.htm.
Vinyl, a manufactured product typically used for home siding, is now available as lumber of decking. For more information on vinyl decking see www.decksanddocks.com.
Composites are virtually indestructible. This lumber is almost impervious to rot and insects. It cuts and nails like real wood and deck screws sink in and disappear. This material is splinter free and as strong as any wood on the market. Like composites, vinyl is impervious to rot and insects, and does not splinter.
- Disadvantages: Both these construction materials are more expensive than redwood, but they will last indefinitely. Composite lumber will lose its color over time and tends to dull as well. Neither material has the look of true wood. Vinyl cannot be used structurally for posts, joints, or joists. Vinyl is also vulnerable to extreme temperature changes, and may chip or crack.
Black and Decker Home Improvement Library. 1992. Landscape Design & Construction. Cy DeCossee Inc., Minnetonka. pp. 31.
Building Products Plus. 1999. "Pressure Treated Wood For Your Project." http://www.bp-plus.com.
California Redwood Association. 1999. "Planning the Perfect Deck." http://www.calredwood.org/homeown/perfdeck/perfdec.htm.
California Redwood Association. 1999. "Literature." http://www.calredwood.org/ref/lit.htm.
Carter, Joe. 1996. Better Homes And Gardens Books: Decks: Your Guide to Designing and Building. Meredith Publishing Group, Des Moines.
Dreamspace. 1997. "Decks." http://decksanddocks.com.
Dreamspace. 1997. "Railings." http://decksanddocks.com.
House of Cedar. 2000. "Decks and Railing," "Fencing." http://www.houseofcedar.com/lumber2.html.
PALCO - Pacific Lumber Company. 1997. "Redwood Decking." http://www.palco.com
Today's Homeowner. 1999. "Decking Decisions." http://www.todayshomeowner.com/exterior/19980706.feature.html
Today's Homeowner. 1999. "Figuring Out Fences - Wood Fences." http://www.todayshomeowner.com/yard/19990531_feature2.html.
Trex - The Deck of a Lifetime. 1999. Wood-Polymer Lumber. http://trex.com/TREX_SITE_1998/TrexECDPage.htm.
This implementation report was developed by Jeff Fahrenholz, student, University of Minnesota Department of Horticultural Science.