How to Properly Choose Treated Wood
To obtain the maximum performance out of your treated wood for any outdoor project, you need to choose material that is appropriate for the conditions in which it will be used. Each piece of treated wood has an end tag that lets you know if the wood is meant for Above Ground, Ground Contact, or Heavy Duty Ground Contact applications. These end use descriptions refer to the types of conditions in which the wood is intended to perform. Below are guidelines on the meaning of those end use descriptions and the best practices in the selection and use of treated wood. All treated wood, regardless of preservative, that is used in residential and commercial applications should be selected and used in accordance with these guidelines. If the right material is not available in your store, ask about special ordering.
Remember, if your project is in contact with the ground or fresh water or built in a manner that does not allow the wood to easily dry, Ground Contact treated wood must be used.
Ground Contact treated wood should be chosen for parts of your project that are:
- in the ground or in contact with the ground
- in contact with debris, leaves or vegetation
- in fresh water
- exposed to daily wetting from sprinklers or other sources of moisture
- in contact with old wood that may be partially decayed
- posts supporting decks and fences (in ground or concrete)
- posts supporting fresh water docks
- all posts when secured by elevated post bases to concrete piers
- all joists and beams when critical and difficult to replace
- stair stringers that sit on the ground or on concrete on the ground
- low retaining walls, planter boxes, and understructure for walkways
- typical Above Ground uses in tropical climates
- material installed over water if it will be regularly wetted by waves and wakes
- less than 6” above ground and supported by permeable building materials
Heavy Duty Ground Contact
Heavy Duty Ground Contact treated wood should be used for:
- posts supporting houses, garages, sunrooms, barns, or other permanent structures (in ground, concrete, or fresh water)
- salt water splash
Wood treated for Above Ground is intended for parts of your project that meets all of the following criteria:
- is not on or in contact with the ground and
- is expected to readily dry out between times it gets wet and
- not located in tropical areas
Some components that are physically above ground still require Ground Contact.
In any of the situations listed above, wood treated for Ground Contact applications must be used even if the members are used in physically above-the-ground applications.
Above Ground applications include:
- deck boards, rails, spindles, lattice, benches, and step treads
- fence boards*
- outdoor furniture, such as Adirondack chairs and picnic tables used on a deck or other well-drained surface
*Fencing should not contact the ground, debris, or vegetation. There should be adequate spacing under the fence boards to ensure airflow and drying.
- Decks should be built to allow good ventilation underneath the deck, and should have spacing between the deck boards. Check the Homeowners / Literature and Resources section of WolmanizedWoodU.com for details on proper installation.
- Wood labeled Above Ground may also be used in above ground interior or weather protected applications.
- Immersion in salt or brackish water requires special treatment outside the scope of this guide.
- Cut ends of all treated wood should be protected with a topical wood preservative solution, generally available online or in paint departments.