If you want your outdoor bench to last (and of course you do!), it is important to select wood types that possess a natural resistance to insects and weather, or, that are made decay and bug resistant by being impregnated with chemicals.
You can choose a wood that grows domestically in North America or you can use a tropical hardwood which grow in equatorial regions. Domestic woods predictably tend to be quite a bit less expensive than exotic woods and have wider availability.
Another choice for outdoor projects is pressure treated lumber, which has been impregnated with chemicals to make the wood moisture and insect resistant. There are good uses for pressure treated wood and it is likely the least expensive option but it may not be the best choice for outdoor furniture.
Listed below are the best naturally resistant types of wood to use when building outdoor benches, garden furniture, or any other outdoor structures.
- Bald Cypress (also called Southern Cypress): (native to southeastern US).
Commonly available in the southeastern U.S. Cypress is affordable in the Southeast but can be more expensive depending on your area. It is strong and has good insect and rot resistance. It is a tan to reddish color (lighter than Redwood). It has a tendency to warp if not dried properly but does not need to be pre-drilled.
- Cedar: (native to northwestern US and southwestern Canada).
Avoid sapwood or streaky surfaces which indicate weakness. Cedar is usually golden-brown which mellows to gray when left unfinished. Cedar is a soft wood and considered structurally weak. In general, Cedar costs about double the cost of pressure treated wood and approximately half of redwood and has very good resistance to moisture and fair resistance to bugs.
- Redwood: (native to west coast of US).
Deep red color indicates the much more durable heartwood–avoid the light colored sapwood. Redwood is relatively soft, use pre-drilled holes to prevent splitting. Redwood patinas to a silvery-gray color. To retain reddish color, use a penetrating clear wood finish or redwood stain. Redwood costs more the farther away from the West Coast of the U.S. you are. Generally costs about 4 times as much as pressure treated lumber.
- White Oak: (native to eastern North America).
Note that this is not the red oak you will find down at your local home improvement warehouse. You’ll need to go to a decent lumberyard to get this strong and hard wood that is very well-suited to furniture making, including outdoor furniture. Quarter sawn White Oak can be especially attractive. This wood is not as expensive as some other hardwoods and has good resistance to moisture and insects.
Many tropical woods are extremely bug and rot resistant. Teak (native to southern Asia), for example, is an extremely stable wood that is as strong as oak with an attractive grain and has excellent resistance to moisture and bugs, however, it has been extensively exploited for more than a century and is becoming less and less available.
Some tropical hardwoods, such as Ipe (also known as Ironwood or Pau Lope) is 2x as strong as oak and even more durable than cedar or redwood. (Ipe can cause respiratory or dermitatis reactions, wear a mask when working with it). They can last as long as 40 years. On the other hand, these woods are typically, very expensive and have limited availability. They tend to be quite hard and require predrilling.
It is also important to consider whether a particular wood species is being harvested in a responsible and sustainable manner. This is especially true for tropical hardwoods, many of which are from endangered rainforests. Look for FSC-certified wood or find out more by going to the Forest Certification Resource Center’s.
Other woods that have a natural resistance to rot and insects include: Arizona Cypress, Catalpa, Black Cherry, Chestnut, Juniper, Black Locust, Mesquite, Red Mulberry, Osage-orange, Sassafras, Black Walnut, Pacific Yew.
To prolong the life of your outdoor furniture, don’t ever leave it in direct contact with the ground and try to keep it out of direct sunlight. Most decay resistant woods should be treated with a penetrating finish (enamel paint, stain, or sealer) to prolong their lives.
California Redwood Association, http://www.calredwood.org/index.htm
Forest Stewardship Counsel, http://www.fscus.org/faqs/fsc_products.php?link=4
NAHB, Wood Exposed Outdoors, http://www.toolbase.org/Building-Systems/Landscaping/wood-exposed-outdoors
University of Minnesota, Selecting Wood for Outdoor Structures, http://www.sustland.umn.edu/implement/selecting_wood.html
Western Red Cedar Lumber Association, http://www.wrcla.org/index.htm