More than 2 million decks are built and replaced each year in North America. It is estimated that of the 45 million existing decks, only 40% are completely safe!
Because decks appear to be simple to build, many people do not realize that decks are, in fact, structures that need to be designed to adequately resist certain stresses. Like any other house or building, a deck must be designed to support the weight of people, snow loads, and objects. A deck must be able to resist lateral and uplift loads that can act on the deck as a result of wind or seismic activity. Deck stairs must be safe and handrails graspable. And, finally, deck rails should be safe for children by having proper infill spacing. Rails should be no more than 4 inches apart (measured from the inside of the rail) to keep small children and pets from squeezing through. This is especially important if your deck is elevated.
A deck failure is any failure of a deck that could lead to injury, including rail failure, or total deck collapse. There is no international system that tracks deck failures, and each is treated as an isolated event, rather than a systemic problem.
Very few municipalities perform investigations into the cause of the failure, and the media are generally more concerned with injuries rather than on the causes of collapses. Rail failure occurs much more frequently than total deck collapses; however, because rail failures are less dramatic than total collapses and normally don’t result in death, injuries from rail failures are rarely reported.
Here are some interesting facts about deck failure and what you can do to SAFETY READY your deck:
- More decks collapse in the summer than during the rest of the year combined.
- Almost every deck collapse occurred while the decks were occupied or under a heavy snow load.
- There is a slight correlation between deck failure and the age of the deck.
- About 90% of deck collapses occurred as a result of the separation of the house and the deck ledger board, allowing the deck to swing away from the house.
- The two most common ways to correctly attach a ledger to a structure are with lag screws or through-bolts. The installation of through-bolts requires access to the back-side of the rim joist which, in some cases, is not possible without significant removal of drywall within the structure.
- Ledger boards should not be supported by stone or brick veneer.
- Ledger boards should not be attached directly (surface-mounted) to stucco or EIFS, either. Stucco and EIFS have to be cut back so that ledger boards can be attached directly to band joists; however, cut-back stucco and EIFS are difficult to flash and weather-proof.
- Decks should not be attached to overhangs.
- Many more injuries are the result of rail failure, rather than complete deck collapse.
- Push on railings and banisters to make sure they’re secure. They should be able to handle 200lbs of force.
- Deck stairs are notorious for lacking graspable handrails.
- Tighten any loose fasteners (nails, screws, or anchors) and pound in any nails that have popped up.
- Rusted or corroded fasteners need to be replaced because they can cause the surrounding wood to deteriorate.
- Rot is wood’s worst enemy, so check several different areas of the deck to be sure the wood is still sound.
- Many high decks are supported with 4″x 4″ posts. Tall 4″x 4″ posts twist under load and 4″x 4″ posts, even when treated, decay below grade too quickly. In all but the lowest of decks, deck posts should be at least 6″x 6″, and be no higher than 12 feet; 14 feet is acceptable if cross-bracing is used.
- Many girders are improperly positioned to where they are relying on the sheer strength of lag bolts. Girders should bear directly on unnotched posts.
- Aluminum flashing is commonly available but should not be used. Contact with pressure-treated wood or galvinized fasteners can lead to rapid corrosion of aluminum.
- There are three ways a joist can be attached to a ledger:
- The first is by resting the joist on a ledger strip.
- The second is by notching over a ledger strip.
- The third is by hanging the joists with joist hangers. And joists should be fully resting in their joist hangers.
- Decks greater than 6 feet above grade should have diagonal bracing from posts to girder, and from posts to joists.
- Free-standing decks (not supported by the home or building) should have diagonal bracing on all sides.
- Guardrails should be supported by posts every 6 feet.
- Decks that are greater than 30 inches above adjacent areas should have guardrails around the edges.
- Decks should not be located where they might obstruct septic tank accesses, underground fuel storage tanks, well heads, or buried power lines.
Reggie Russell - Owner.
