There have been many deck failures, which resulted in injury and death in the last year. The true condition of decks is always an issue with existing homeowners, prospective homeowners, property managers, and realtors.
Many of the states including North Carolina have updated there inspection requirements due to recent deck failures. Forty million decks in the US are more than twenty-years old. The decks were built prior to the development of new codes. Between 2000 and 2008, there were 30 deaths from deck failures. When a deck collapses, 75% of the occupants are injured. - North American Deck and Railing Association (NADRA)
About fifteen years ago, I witnessed a failure at my neighbor’s house. It was very scary. Our houses were built in 2003 so the deck was about seventeen years old. I had warned him on a visit to this deck that I thought the nails were pulling loose from the stringer for the stairs to his deck. He proceeded to tell me that he had grown up in construction and thought that it was just fine. I was on my deck as he decided to descend into his back yard from the deck steps late in the afternoon. As he hit the second step, the stairs collapsed. Lucky for him, he was not injured.
Causes of failures:
The ledger board pulls away from the house. Most decks in this area have the ledger board attached to the band joist of the house. In many cases, this connection was made with nails before the new standards were set. Newer construction requires bolting to the band joist with 5/8” hot dipped galvanized bolt with nut and washer and 12d galvanized nails. An exception to this is to use self-drilling screw fasteners. Some decks have post supports around the perimeter.
The ledger board fails from splitting. This happens when the fasteners for the ledger board attachment to the band joist are not staggered.
Rotted boards. When the ledger boards are not properly flashed, the board my rot prematurely from weathering. All exposed boards should be decay resistant and properly flashed at the band joist.
Hanger nail and toe nail failure. Historically, decks were built only using nails. In addition, the deck joists were only toe nailed to the ledger with no hangers or ledger strip. In some cases, the joist hangers fail due to corrosion of the fasteners or rotted wood.
Post or column failure. One of the primary causes of failure is the rotting of post or beams. Then again, the components may be undersized. If the post were set in the soil without protection, they may rot to the point of failure. If the beams of the deck have not been properly maintain, then large loads, like a family gathering, can cause failure.
Joist failure. This type of failure is not as drastic as typically only one section of the joist my fail from rot. However, this may mean a leg goes through the floor. The entire deck typically will not fail and calls for replacement of joist and possibly the floorboards.
Footing failure. In some cases, I have seen decks that do not have any footing with the post sitting directly on the ground. Alternatively, they may be placed on uneven rocks that do not give structural support. Alternatively, the footings may be simply undersized. This is sometimes very difficult if not impossible to tell from a visual inspection.
Other concerns. For freestanding decks, cross bracing is very important to prevent the deck from failing. For attached decks, there is no diagonal bracing for the post on the outside girder line parallel to the house. Pickets on the deck may not meet the present standard of a four inch or less opening. There may be no railing on the deck when the deck floor is more than thirty inches above the ground.
Decks should be inspected regularly. If you have never had your deck inspected, the time is now. If you have concerns, then contact your licensed home inspector, a licensed general contractor, or a licensed specialist in deck construction.
Thanks for reading. Let me know if you need a deck inspection. - Mark