WOOD IS THE MOST COMMONLY USED BUILDING MATERIAL IN RESIDENTIAL CONSTRUCTION. THOUGH WOOD IS A PLENTIFUL, RENEWABLE RESOURCE, IT ALSO HAS A WEAKNESS THAT OTHER COMMON BUILDING MATERIALS SUCH AS STEEL AND PLASTIC DON'T HAVE: IT CAN BE SUSCEPTIBLE TO FUNGUS, INSECTS, AND BACTERIA. TO PRESERVE IT, WOOD MUST BE TREATED WITH CHEMICALS BEFORE IT'S USED FOR DECKS OR OTHER OUTDOOR STRUCTURES.