THE CAUSE AND PREVENTION OF A MAJOR DECK COLLAPSE
The North American Deck and Railing Association or NADRA estimates that there are 40 million decks in the U.S. that are over 20 years old. The concerns with older decks are:
- Many were built before new codes were established which made decks uniformly safer.
- Many are weaker after experiencing weather stress for many years. These weaknesses are more severe in our coastal environment.
- Some have not been properly maintained.
The condition shown on the right (COMPLETELY corroded nut and bolt which flakes away when touched) was found under a pedestrian walkway at a local Outer Banks retail establishment and is a typical condition, especially for decks located near the ocean. Heat, ultraviolet light, elevated moisture levels, and salt spray exact a stiff toll on wood decks and their metallic connections in relatively short periods. A condition like this should raise safety and liability concerns for both the owner and rental agency.
Below are some headlines and links to deck collapses which have occurred just over the past 12 months.
-Myrtle Beach, SC – June 7, 2014
-Pawleys Island, SC – Jun 09, 2014
-Ocean Isle Beach, NC – Jul 13, 2013
Typical coastal areas like the Outer Banks are home to thousands of decks which are constantly being compromised by the harsh salt water environment and violent storms. Often these homes are investment or rental properties which pose a substantial liability if and when the deck structure fails. Decks in the coastal areas should be inspected yearly and after each major storm event. It is advisable to hire a professional contractor or engineer to inspect your deck and its connections but that’s not to say you cannot inspect your deck yourself. Here is what to look for.
Ledger Bands: The ledger band is typically a 2×10 or 2×12 treated wood member running perpendicular to the deck joists. It should be bolted to the homes structural frame, thereby providing a secure connection on which all other deck framing members are attached. The ledger band and associated ledger are the number one source for all deck collapses. Current building codes require that the ledger band is secured through the house structural framing with 5/8” HDG (hot-dipped galvanized) through bolts every 32” on center. When inspecting your deck, be sure that the galvanized bolts are installed. A ledger band that is secured with nails only will certainly fail sooner than one secured with through bolts. Be sure that the installed bolts are in good condition and not rusted. Corrosion to the surface of the bolt is acceptable but deep penetrating rust is a sure sign of a weak connection and potential hazard.
Deck joist ledgers: A deck ledger is typically made up of a 2×2 or 2×4 treated wood member attached to the bottom of the ledger band. Its sole purpose is to provide vertical support to the deck joists sitting on top of it. In coastal area construction, a wooden ledger is used in lieu of metal joist hangers for joist support. In a salt water environment, metal joist hangers can corrode and ultimately fail and in our area they have been substituted with wood. Currently, the building code requires a 2×4 ledger with 5-10d HDG nails under each joist. A lot of older homes have 2×2 ledgers with 3 nails under each joist. In any case, the key to a lasting deck ledger is in its fasteners/connections. Check the nails that support the ledger for corrosion and rust. These fasteners should be in good condition. If your deck is supported with metal joist hangers, inspect the hangers as well as the nails used to secure the hangers. Rust and corrosion is the enemy here and the most common reason for deck failures.
Deck girders: Running parallel to and on the opposite side of the joist ledger and ledger band is the deck girder. A deck girder is located away from the house and usually supported on each end by a piling or post. The deck girder should be connected to the piling or post with through bolts at each end. Current code requires (2)-2×10 treated wood members spanning no more than eight feet on center and secured by (2)-5/8” HDG through bolts at each end. This connection is typically not a failure point but some areas to review are the following: the bolts which connect this supporting beam to the pilings should be free of deep rust and corrosion and the beam should be inspected for sagging. Over time many beams and girders can sag and in turn, the deck and decking follow suit.
Joists: Deck joists are typically as small as 2×6 but on average are made of 2×8 treated wood, depending on their span. For longer spans they can be as large as 2×10’s. Joists run from the ledger band at the house out to the deck girder. At the house the joists butt up against the ledger band and sit atop the joist ledger and at the other end the joists sit atop the girder. During an inspection, be sure the joists are sitting securely on top of the joist ledger and girder at each end. The joists should also be toe nailed into the ledger band and the end band over the girder. Also check the nails for corrosion and rust. In addition to the connections, you should inspect each joist for sagging. If the joists were not properly sized the joists may sag or crack over time.
Decking: The decking is rarely at fault when a failure occurs. The decking is like the hardwood flooring in your home. Its sole purpose is to provide a surface to walk on and span a very short distance (usually 16″) between joists. The decking tends to take all the wear and tear from the sun, wind and rain. In older decks the decking can look much worse than anything you see in the structural members of the deck. For the decking, simply be sure that the deck ends are nailed down properly to prevent tripping. Screws are better than nails for this purpose and will last longer. The typical reason for decking remediation is cosmetic, not structural.
Railings: The railings are the safety net for the deck. In our area decks can be twenty feet off the ground or more which in itself is a safety hazard. The easiest way to check your railing is to simply grab and shake back and forth. They should feel solid, not move and give you a sense of security. It is absolutely crucial to have safe, secure deck railings at all times. The rail post is the most susceptible to failure. If you keep the supporting posts attached to the deck securely, the railing will stay secure. Current codes require a minimum of a 4×4 wood post secured to the joist band with 2-1/2” HDG through bolts. A typical Outer Banks home might have 4×4’s notched and nailed to the joist band. This is a very weak connection. Notching the post reduces the amount of bolted cross section at the fulcrum of the post. Over time this connection will be subject to great stresses and become loose or split at the notch. And with only nails securing the post, it may fail if someone simply falls into the railing. The best connection is to drop the entire post inside the outboard joist band, block the base of the post and install (2)-5/8″ through bolts at each connection. If your deck has bolted connections and the railing seems firm, simply inspect the connections for rust and corrosion.
Your coastal area decks, like everything else in or on your home, require constant maintenance. A poorly constructed and maintained deck is a hazard in general but a huge liability in a rental-investment home market. The likelihood your deck may collapse increases every year and with every violent coastal storm. Take a minute to inspect your decks and be sure to call a professional engineer or Outer Banks Builder if you find anything concerning.
-blog by Barrett Crook, Kitty Hawk Engineering and Michael York, The Coastal Cottage Company | Outer Banks Builders