The weakest link in your deck – a risk of collapse

Placeholder while loading article actions Bridge collapses happen all the time, and many of them never make the headlines. Several years ago, I attended a one-day training session given by a major manufacturer of metal

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Bridge collapses happen all the time, and many of them never make the headlines.

Several years ago, I attended a one-day training session given by a major manufacturer of metal structural connectors for decks, houses and other structures. They estimated at the time that over 80% of bridges in the United States are structurally flawed and are ticking time bombs. This speculation is staggering and should immediately make your head spin.

My youngest daughter’s roommate was the victim of one of these bridge collapses. She went out on a small terrace four years ago and she detached herself from the building. The woman and the bridge crashed 12 feet off the ground. She was rushed to hospital with a ruptured spleen and a broken neck. She survived but is now partially disabled.

You’ve probably heard that a chain is only as strong as its weakest link. The weak link in the typical bridge is where it attaches to the house. This structural element of the deck is called a ledger board. In reality, it’s not much different from a steel beam you might see in your basement or the ones supporting the bridges you drive under in your city or town.

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A tremendous amount of weight is transferred to this ledger. In most cases, half the weight of the entire deck, all of the furniture on it, and the combined weight of you, your family, and your friends is pushing on that one board. It can be thousands of pounds.

But it’s getting worse. Not only does the weight push down, but if you and your friends start dancing on the bridge creating a seamless side-to-side motion, you can exert a force that begins to pull the bridge away from your house. It’s a recipe for disaster if the ledger board or untreated wood outside your home has rotted away because the ledger wasn’t installed properly. Which is why my daughter’s roommate was lying unconscious on the floor that fateful day.

It is important to realize that treated wood can and does rot. I witnessed it myself. Every day when I go out for a walk, I pass treated wood railing posts as rotten as logs lying around in the forest just 50 feet away. Keep in mind that not all treated woods contain the same amount of chemical preservatives. Also, how do you know if the wood has been properly treated? A number of things could have gone wrong at the treatment plant. Substandard products of all types are being produced all the time. This is why there are product recalls on an almost weekly basis.

Do you, by any chance, remember any part of your high school chemistry? Have you done any laboratory experiments on galvanic reactions? Every time it rains on your patio, a toxic brew is created. Rain leaches copper from treated wood. This liquid attacks any exposed steel or iron. If your deck was built using inferior fasteners with a thin layer of zinc, they could be corroding as I type this. This same corrosion can occur with any of the joist hangers and other framing connectors.

All this is exacerbated if your terrace is located in a marine environment. Sea salt is also corrosive. I went on my first cruise a few years ago and attended a lecture given by the captain of the ship and his two best crew members. I will never forget when they spoke of the constant battle they face with sea water. The captain said in his strong Eastern European accent: “The sea eats iron and men.

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You need to improve your game if your deck is exposed to sea conditions. If it was me, I would use as much stainless steel as possible for fasteners, bolts, connectors, etc. Anything other than stainless steel should be double-dipped hot-dip galvanized metal. I would also do annual deck inspections to ensure corrosion is minimal or non-existent.

Over the years, I’ve discovered a surefire way to prevent rotting deck boards. I’m not the only one who’s worked in this area, but my method is the only one I’ve seen that incorporates two different techniques that work together to keep deck boards and primary connectors as dry as possible.

The only trick is to use firestops on the joists, something master carpenters discovered over a hundred years ago when they installed floor joists in solid brick buildings. As cities grew, brick buildings got taller, and firefighting became more professional, it became abundantly clear why firefighters got killed when brick walls collapsed. The walls of buildings that did not have angled firestops at the ends of the joists swung outward, overwhelming firefighters when floor joists burned and broke in two inside the buildings. This can be adapted to the construction of the bridge. The second trick is to use a kick on the all-important flashing that covers the top of the deck ledger board.

I prepared a color illustration to show how I would install your patio damper so it doesn’t rot or drift away from your home. This document also contains links to the best deck hardware and fasteners, the most important special connection anchors, and the best treated lumber to use when building your deck ledger board. You can get it all here:

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