Each Summer there are reports of deck collapses, as groups of people head outside to enjoy the warmth of the season. Even though there are construction standards for safely constructing decks, it is surprising how often I come across poor deck construction practices.
The first thing I look for when I crawl under a deck is to check on how the ledger board is attached to the house. A ledger board is the horizontal beam attached to an existing wall and used to support and anchor the deck to the house. It’s usually a 2×10 or 2×12 piece of lumber. Best practices for installation is to either use lag bolts that are secured into the rim joist or a ‘through’ bolt that extends through the wall and is secured with washer and nut inside the house. Of course, it’s possible to use the right material in the incorrect way!
When I want to remove a check from my checkbook, I always fold along the perforated line before tearing. The perforations are in a nice, straight line and it’s usually pretty easy to remove the check. When deck installers place lag screws (or LedgerLok screws) in a straight line, the ledger board is essentially getting perforated. Over time, and with activity on the deck, the ledger board can start to fold along that ‘perforation’, crack and potentially fail.
The above photo shows a ledger board with in-line lag bolts and cracking beginning. The solution (below) to this failure is to place the bolts two inches from the top and bottom of the ledger board in a zig-zag pattern (one up, one down) along the length of the ledger.
There is one fastener that I see on occasion that is truly irresponsible: nails. It doesn’t matter how large or how strong the nail: nails should not be used to attach a ledger board. Wood swells with moisture and shrinks with heat and age. The nails will eventually lose their grip and the ledger will pull away from the structure. Whenever I observe this happening, I advise the clients to keep off until a qualified carpenter can be contacted to properly secure the deck.
The ledger attachment is often either a good indicator that a deck contractor knew what they were doing or a warning sign to pay extra special attention to a poorly constructed deck.