In a recent safety evaluation of residential decks in and around Charlottesville Virginia an alarming trend was noted. 7 out of 10 decks had at least one safety issue, and 4 of the decks had significant safety issues that were cause for immediate action. Most homeowners either hire a contractor to build the deck, or the deck was attached to the house when the home was purchased. Some of the most serious issues found were:
Insufficient methods of attachment to the house Improper joist fastening Insufficient lateral bracing Improper or non-existent post attachment Undersized framing members Improper fasteners used

The most serious issue, insufficient attachment to the house, was found on almost half, 4 of 10, of the decks inspected. When a ledger board, or band board (the framing member of the deck that is fastened to the structure of the house, to which the joists of the deck are attached) is fastened to the house improperly, the deck is a critical risk for collapse. Ledger boards MUST be fastened to the house using either lag bolts that fasten securely to the rim joist or framing of the house, or carriage bolts that completely penetrate the framing of the house and are secured with a washer and nut on the other side. The issues we saw included the use of nothing more than 16 penny nails, lag bolts that missed the house framing members and were fastened only to the exterior sheathing (plywood) and on one case, standard wood screws. Improper fastening techniques and materials is the #1 cause of deck collapse, leading to injury and death. When a deck is utilized for entertaining, the shift in load when people move about on the deck also shifts the stresses on the deck structure. The more people, the more weight, and the greater the forces involved. One of the decks we inspected was so poorly constructed, one person’s weight was enough force to cause to deck to sway slightly. Put 20 people on that deck, and everyone is at risk.

16 penny nails are just not thick enough to withstand heavy loads and have very little strength to withstand lateral forces to resist pulling out. Any adult can pull a nail with a hammer claw using about as much force as is equal the force of 30 pounds of weight. Put 20 people, over 2,000 pounds of weight force, on a deck fastened with nails, and you see the problem. Nailing, bolting or even lag screwing to the exterior sheathing of the house is essentially useless. Most exterior sheathing products are less than 1/2 inch thick. They are designed to supply lateral (sideways) strength to a structure, not to resist pull-out forces. The best method of attachment is to utilize carriage bolts that go completely through the deck’s band board, through the house band board or other framing member, and are secured with a washer and nut on the other side. When this is not possible, lag bolts must be used and must be secured into the framing members of the house.

The next serious issue noted was found with the fastening of the deck joists to the deck band board. Again, in nearly half of the decks inspected, the joists were merely toe-nailed to the band board, and/or toe nailed and sitting on a 2X2 inch ledger block placed under the joist. The same issues of poor pull out resistance and load carrying ability apply here. The only correct way to fasten deck joists is to utilize a metal joist hangar. They are designed to carry the load and withstand lateral forces when used properly. Check under your deck. If you do not see joist hangars, nailed at 90 degrees into the band board of the deck and into the joist, your deck is not safe!

Most of the decks inspected utilized 4X4 treated wood posts that were both buried in the ground below the frost line and sitting atop a proper concrete footing. A few of them were not. Two of the decks had 4X4 posts literally just resting on top of concrete, with no attachment method to the concrete. If you are not burying the post at least 2 foot below grade, then you must utilize a metal post base bracket. The post base it attached to the concrete using the appropriate concrete fasteners, then the post is attached to the bracket using joist hanger nails or lag bolts.

Next, a serious lack of lateral bracing on most of the decks was noted. Lateral bracing prevents the deck structure from moving sideways. If you were to start out taking a few steps on one direction on your deck, and stop suddenly with force, your deck should NOT MOVE. If it does, it is not properly braced. Your deck should be at least as strong as the floor inside your home, and often stronger. The exterior sheathing on the structure of your house provides the lateral bracing. On a deck, it needs to be done with dimensional lumber that is designed to withstand exposure to the elements. When properly planned, a deck’s lateral bracing can be incorporated into the design so that it adds to the appearance of the deck while providing a structural purpose. If your deck is built on grade, or less than 24 inches above grade, lateral bracing will need to be applied before the deck surface is placed. On decks more than 24 inches above grade, an angled piece of dimensional lumber should be fastened to each side of each post, from the top of the post to some point below the top, with a minimum of a 30 degree angle. If you have a deck, get it inspected by a professional immediately. An inspection should take about an hour, and cost less than one hundred dollars if you call a contractor. A small price to pay for peace of mind.

By: Tom Schlegel