• Much planning goes into the creation of an outdoor deck.Michael Turek/Photodisc/Getty Images
  
  Just because it's an outdoor structure doesn't mean that a deck doesn't need to meet structural guidelines. Not only must the deck design show that it meets local code requirements for a deck support system and floor, but it must also meet local stairway and deck railing requirements. Local building codes may limit the size and placement of outdoor decks as well.
  
  

Deck Support

• No deck is structurally sound without the proper support posts. In most instances the posts may be treated 4-by-4-inch lumber, but if the deck is more than 8 feet off the ground, 4-by-6 or 6-by-6-foot posts may be necessary. If the deck must support extra weight, such as from a large grill, the larger posts may be necessary as well to prevent the deck floor from sagging. Posts made of stronger woods, such as Douglas fir, western larch, coast Sitka spruce, Western hemlock or Southern pine are a better choice than posts made of other types of wood. The spacing of the support posts is also crucial to having adequate deck support. Following industry standards for the placing of posts, as well as support beams and floor joists, can help ensure your deck has the proper support for the deck floor.
  
  

Deck Railing

• As a general rule of thumb, the closer the deck is to the ground, the shorter the deck railing requirements are. In most municipalities, if the deck is less than 30 inches off the ground, no railings are necessary. If the deck is between 30 inches and 5 feet 10 inches above ground, the railing must be at least 36 inches tall. For decks taller than 5 feet 10 inches, most codes require a 42-inch rail. The railing must be solid enough to support at least 200 lbs. at any point on the horizontal rail. If the weight hangs off the rail, such as a hanging planter, the railing needs to simultaneously support 50 lbs. vertically plus 100 lbs. horizontally. If the deck railing incorporates glass, it must be tempered glass that doesn't break into shards. The decorative upright posts must not be any farther apart than 4 inches, or spaced closely enough to keep a young child from getting his head caught.
  
  

Deck Stairs

• Deck stairs must be at least 35 inches wide and have a handrail that's 1 1/2 to 2 inches in both width and thickness. The stair treads must not have a rise of more than 7 3/4 inches. The treads should be at least 9 1/4 inches wide. The two stringers that support the stair treads must each be 1 1/2 inch wide. If more than two stringers support the stairway, the stringers may be 1 inch wide. Building codes require that stringers set on poured concrete or cement blocks to prevent rot. In any case, the stringers should be pressure-treated lumber, which is rot-resistant.