More than a million decks are built and replaced each year in the United States. While decks are a popular feature of many homes, the unsafe construction of decks has become a real concern within the building industry due to the number of deck failures and related injuries and deaths. Most experts agree that the average life expectancy of a deck is 10 to 15 years. Since deck building began in earnest over 30 years ago, there are many existing decks that are past their safety life. Like a house or any other building, a deck must be designed to support the weight of people and objects placed on them as well as lateral and uplift loads as a result of wind or seismic activity.
MAINTENANCE OF EXISTING DECKS: It is important that decks are properly inspected and maintained on a routine basis. If unsure, it is best to consult with a professional, such as a structural engineer or reputable contractor, to make sure the deck is safe. Here are some areas to check when inspecting the safety of an existing deck:
Missing, loose, or corroding connections can compromise the safety of the deck. Toe nailing (see glossary) does not constitute a proper connection. Issues such as wobbly railings, loose stairs, and ledgers that appear to be pulling away from the house are all cause for concern. Metal connectors and fasteners can corrode over time, especially if a product with insufficient corrosion resistance was installed. Wood rot and cracks: Wood can rot over time with exposure to the elements, and with sufficient rot the deck frame may no longer be able to safely support the deck. As wood ages, it is common for cracks to develop, and large or excessive cracking can weaken a deck as well.
DESIGN / INSTALLATION GUIDELINES: It is important that an engineer or other qualified professional evaluate the design of a deck to determine the specific number of fasteners and their spacing for any specific deck installation. Here are some areas to consider with your builder:
LEDGERS: (See Glossary) Correct ledger attachment is crucial when building a deck that is attached to another structure. One of the most common causes for deck failure is ledgers that pull away from the primary structure, resulting in complete collapse. The two most common ways to correctly attach a ledger to a structure are lag screws or through-bolts through the ledger and into the rim joist of the supporting structure. Ledger must not be installed over siding or stucco but directly to the rim joist, stud, or sheathing.
POSTS, COLUMNS, FOOTINGS: (See Glossary) In order for posts to properly resist various types of loads, they must rest on and be anchored to concrete footings. Patios and pre-cast concrete piers do not qualify as proper footings for deck construction. Footings should be at least 12”" below the undisturbed ground surface, and should be a minimum width of 12". Columns should be restrained to prevent lateral displacement at the bottom end. Wood columns should not be less in size than 4"” X 4”". Column and post-end connections should be fastened to resist wind. Wood Columns should be of an approved wood with natural decay resistance or approved preservative-treated wood.
JOISTS, BEAMS, GIRDERS: (See Glossary) When joists terminate into a beam or ledger, a connection is required to provide bearing and must be able to resist uplift. At the point where the joist bears on top of a beam, there must be a connection to resist lateral and uplift forces. Blocking or framing is also required thus preventing overturning of the joists. Joists must be supported laterally at the ends by solid blocking or attachment to a full depth header, band or rim joist. Lateral restraint must be provided at each support
RAILING POST-TO-DECK FRAMING: (See Glossary) The railing connection is one of the more critical connections pertaining to safety, and it is often inadequately constructed. The post must not only be fastened to the rim joist, but also tied back into the joist framing. Machine bolts through the post and rim joist alone do not typically meet the performance requirements of the code. Guards should be located along open-sided walking surfaces more than 30’" above ground below and be a minimum of 36" high.” Handrail and guards should be able to resist a single concentrated load of 200 pounds applied in any direction at any point.
STAIR STRINGERS & TREADS: (See Glossary) Stair stringers must be connected to the deck, and treads properly connected to the stringers in order to resist loads. Staircases must be able to resist 40 pounds per square foot of tread area. Individual stair treads should be able to resist a 300 pound concentrated load over an area of 4 square inches. The openings formed by the riser, tread and bottom rail of the guard at the open side of the stairway should be 6" high at a maximum.