Deck collapses happen more often than you may thing, and many never make the news.
My youngest daughter’s roommate experienced a deck collapse. She walked out onto a small deck four years ago, after it had detached from the building. Both the woman and the deck crashed 12 feet to the ground. She was rushed to the hospital with a ruptured spleen and a broken neck. She survived, but she suffered life-altering injuries.
You’ve no doubt heard the saying that a chain is only as strong as its weakest link. The weak link of the typical deck is the place where it attaches to the house. This decking structure is called a ledger board. It’s not unlike the steel beam you might see in your basement or the beams supporting bridges you drive beneath.
An enormous amount of weight is transferred to the ledger board. In most cases, that’s half the weight of the entire deck, deck furniture and people on the deck. This pressure exerts thousands of pounds of force onto a single board.
If your deck is made from treated lumber, it’s important to realize that this material can and does rot. Treated lumber varies when it comes to the volume of chemical ingredients that were used to preserve it. And how do you know if the wood was properly treated?
In addition to wood rot, galvanic corrosion may undermine the strength of the steel or iron materials used to build your deck. Rain leaches copper from treated lumber, and this coppery liquid attacks any exposed steel or iron. If your deck was built using fasteners topped with a paper-thin coating of zinc, they might be at risk of corroding. This corrosion can also occur on the joist hangers and other metal framing connectors used in your deck’s construction.
These issues are amplified even more in a marine environment. Sea salt is also corrosive. If your deck is exposed to marine conditions, I recommend using as much stainless steel as possible for fasteners, bolts, connectors, etc. Whatever isn’t stainless steel should be made from double-dipped, hot galvanized metal. Inspect the deck annually to ensure corrosion is minimal or nonexistent.
I’ve discovered a way to stop ledger board rot, using a method that incorporates two different techniques to keep deck ledger boards and their primary connectors as dry as possible. The first trick is to use fire cuts on the joists, something master carpenters figured out over 100 years ago when they installed floor joists in solid brick buildings. These builders found that when walls of buildings lacked angled fire cuts on the ends of the joists, they would tip outward when strained. This can be adapted to deck construction. The second trick is to use kick-out flashing above the deck’s ledger board, which prevents water intrusion.
Tim Carter has worked as a home improvement professional for more than 30 years. To submit a question or to learn more, visit AsktheBuilder.com.