Pressure-treated wood is the best choice for decay resistance. On the West coast, builders commonly choose redwood or cedar which contains natural oils that discourage insect penetration and decay from moisture. A common choice among East coast builders is southern yellow pine which has been pressure-treated with chromate copper arsinate (CCA). Wood treated with CCA can be used in direct contact with the ground. However, because CCA is essentially a very powerful poison, it is advisable to not place food or other edibles directly on a CCA-treated surface. It is also advisable to wear a protective mask when cutting CCA-treated wood to avoid inhalation of the chemical.
Better construction design can go a long way in minimizing wood decay in decks. The design should minimize the concentration of moisture by leaving gaps where possible to encourage water drain-off. Another good rule of thumb is to avoid as much as possible the vertical exposure of board end-grains.
For decks, staining is preferred to painting completely exposed wood. A water stain with a pigment and a preservative is recommended. All woods, even pressure-treated lumber, need protection from the sun. The heavier the pigment, the better the level of protection.
Deck Support / House Attachment
Deck supports must be on a firm base. Lag bolting to the house is the preferred method of attachment. Attachment must be to the house structure itself and not just the siding.
When adding a deck, make it a point to install flashing from under the house siding to below the deck attachment to prevent water from being trapped against the house, which can lead to rotting and insect infestation. If the deck has already been built and attached to the house, but proper flashing was not done, then sealing with an exterior caulking compound will improve the situation. The caulked areas should be a part of the annual inspection of the house exterior to ensure moisture-free integrity.