This from the New York Times…..
A large holiday party ended abruptly Saturday night when a second-story deck collapsed and plunged 10 feet onto a concrete patio, injuring more than 30 people.
The Point Pleasant Beach police said that 11 to 25 people were on the 12-by-20-foot wooden deck at the rear of the two-story beachfront house at 2 Delaware Avenue when it gave way around 9:25 p.m. Several people were briefly pinned in the rubble. Emergency workers from Point Pleasant Beach and several surrounding towns arrived and set up a triage area to assist them.
Thirty-three people were taken to local hospitals and treated for injuries ranging from lacerations to sprains. By Sunday afternoon, only one woman remained hospitalized, at the Jersey Shore Medical Center in Neptune, N.J., where she was recovering from surgery, according to a police spokesman.
After an inspection, town officials said the deck did not violate any building codes, although it was nailed, rather than bolted, to the house. Bolting is now required, but because of its age, the deck was grandfathered under an old law that did not require bolting.
This is why you should never be reassured by the fact that a building meets code. The building code is far stricter in New Jersey then it is in many other parts of the country (like where I live for example). And yet they grandfathered in nails as a load bearing device on a two-story structure.
If a ledger that was fastened to the building with nails had affected the way the neighborhood looked, they never would have allowed it. But since it was “just a deck” nobody thought that the structural details were that important.
But I will save my rant on codes for another time. The sad fact is that deck failure kills people all over the country every year. When decks collapse the cause is almost always ledger failure. And the ledger failure is almost always blamed on builders who use nails to tie the ledger into the house’s structure instead of lags (frowned on by experienced builders but better then nails) or bolts (the approved method).
At least that is what most sources on the web say, but I happen to believe that there is a little more to the story then rogue builders using nails. Before we get to what I think is the untold story of the ledger failures, let us take a look at the broader picture of why decks are so poorly built.
In the first place, it must be acknowledged that decks are a very unnatural use of wood. If you look around at all the trees you will see that most of the wood in them is vertical and all the wood is covered with bark. Throughout history, carpenters have understood that nature dictates the proper way of using wood. So they have used it in manner that imitates how it is found in nature. They primarily used wood as a vertical support and they always took care to protect the wood from the elements.
But decks throw all of those old rules out the window. By design decks put a lot of wood in exposed horizontal positions. For the first time in building history, naked wood was expected to deal with rain, snow, and anything else Mother Nature could throw at it. The only reason this idiocy ever even became possible was through the advent of pressure treated wood.
But even that poisonous cocktail cannot preserve an unnatural creation for long. According to the National Association of Home Builders, the average wood deck only lasts for 15 years. You can extend that figure if you are really religious about keeping up the maintenance of your deck. But the inescapable fact is that your deck is not going to outlast your mortgage no matter how you treat it.
Since even the best builders are going to see there wood decks fall to pieces in a relatively short time span, you can see why it is critical to do things right. When you are trying to do something that is unnatural, you have to be very careful. Every mistake just makes the time period before the deck comes down all the sooner.
But the very unnaturalness of decks makes mistakes all the more likely in deck construction. That is because it has only become possible to do this unnatural method recently. This means that decks are a relatively modern invention. The first modern decks were built in the south at the dawn of the infamous baby boom generation. As the baby boom generation has grow up and grown wealthier the number of wooden decks grew right along with them. Now that the baby boomers are at their peak earning potential, decks are practically a must have.
The fact that decks are barely a generation old makes mistakes more likely for a couple of reasons.
In the first place many tradesmen are tradition oriented. That is to say, they don’t really understand the reason why they do certain things; they just do them that way because that is the way things have always been done. Since deck building does not have much of a tradition behind it, a lot of people in the trades try to apply traditional carpentry practices to deck building. But because decks are unnatural creature, this creates problems.
The second reason why the recent origin of decks causes problems has to do with the nature of the social changes brought about by the baby boomers. It used to be that the trades were a perfectly respectable occupation. But starting with the baby boomers, the trades became a place to dump people who were unfit for any other activity. The only people who were encouraged to join the trades were those people who had been given up on by the educational system. Thus, telling someone to become a carpenter became synonymous with saying that they were dumber than a box of rocks.
The natural result of this process was that carpenters went from being men who could build magnificent staircases from scratch to being any fool who could strap a tool belt on. And so we have given up grand staircases in exchange for badly built decks.
Once you understand that decks are unnatural constructs built by the dregs of society without any tradition to guide them, you start to understand why ledger failures are so common. “Carpenters” think that since they can build a two story house with 2X4’s and nails, then they must be able to use nails to support the deck. It is that kind of ignorant reasoning that gets people killed.
To be fair though, the right kind of nails can theoretically support the loads that a deck will be called upon to deal with. The real reason that nails are forbidden has to do with other types of stress that a deck will have to deal with. As this article from This Old House Magazine says….
Using a database to search five years of newspaper articles from around the country, he found that nearly every collapsed deck had been attached with nails, rather than bolts, and that investigators had pinpointed the nails as the cause of collapse. “On paper, you can calculate that nails will work,” Falk says. “In practice, it’s a different story.” As people gather on a deck, their weight and movement translate not just into a downward force but also into an outward force that acts as a lever prying the deck away from the house. Nails work well to resist the downward force but are no match for the outward force. Held in place only by the friction of bent wood fibers, nails tend to loosen when wood alternately shrinks and swells with changes in moisture content and temperature. Once nails loosen, they offer even less resistance to the prying forces of a crowd. “There is no built-in safety factor with nails, no warning of a coming disaster,” Falk says. “When they pull out, they pull out.”
It is the subject of this levering force that brings us to what I consider the untold story of deck failure. The focus in the above quote is the ability of live loads to exert an outward force that pries the nails out. But there is an even more powerful force that will pry those nails out and that is the ground heave that occurs when the frost heaves the ground.
This is an area where the poor quality of the trades really shows up. Bob Mulloy is a professional house inspector and an expert on deck failure. He says….
I like to inspect the deck from the ground up. I start by examining the visible piers or footings at ground level. If I find patio blocks, cement blocks, or five-gallon buckets filled with cement, then I automatically think “red flag” and investigate a little more carefully by probing. Up here in New England, all footings must extend a minimum of four feet below the ground to prevent frost heave, but all too often I must document “shallow footings beneath deck, potential for frost heave movement.”
When I was younger and worked as a laborer for a living I helped a number of people build decks. It was almost always my job to dig the holes for the concrete supports and I can not recall ever being allowed to dig the holes below the frost line.
Even back then, I knew that you were supposed to go below the frost line, and I was more than game to go the distance. But invariably I would slow down the further down I got, and the boss would get impatient and tell me that the hole was good enough. Any protests on my part were dismissed with “I have done this lots of times and I have never had any problems with frost heave.”
They may have been right. The frost line specified by code is not something that is going to be hit every year. The frost might only go to that depth every 15 years or so on average in some places. Moreover, it might not go to the frost line depth in 100 years at sites that are really well drained.
Therefore a lot of builders can get away with not going below the frost line for long periods of time. But the decks they build could kill people after one really cold snap with no snow cover.
This is because the upward force of the frost heave will cause the whole deck to act as a giant pry bar on the ledger (presuming of course, that the deck heaves more the house does). This prying affect will seriously weaken the attachment of ledger to the house even if the deck settles back down by summer time. Thus, a deck that may have supported many a large party will suddenly collapse when exposed to a moderate live load, all because of a hard winter and a deck with improper footings.
But the deck failure will rarely be blamed on the frost. Instead, the inspectors will say that ledger failure was the cause of collapse. While this will be technically true, I think it misses the major contribution of frost heave to ledger failure and thus to deck collapses.
I have spent so much time harping on the unnatural nature of decks and the problem of frost heave for a reason. I believe that focusing on nails as the major cause of deck collapse has misled a lot people. Your average contractor now realizes that it is bad practice to use nails to attach the ledger to the house. That is good thing. But your average contractor also believes that since he does not use nails to attach the ledger then he is building the deck the right way. This is a bad thing.
The study that showed that a nailed ledger was the major cause of deck failure had a couple of flaws. For one thing, the study was an analysis of news stories. But deck failure only makes the news when people get seriously injured or killed. Most researchers freely acknowledge that many deck failures never make the news. Since a deck that fails suddenly is more likely to kill than a deck that gives warning, news stories about deck failures will be skewed towards those that had nailed ledgers.
Furthermore, the study failed to control for how old the decks were when they collapsed, as best as I can tell. This matters because in the past using nails to fasten the ledger was far more prevalent in the past than it is today. Yet it is natural, too, that older decks have a greater chance of failure than newer decks, no matter how they are built. So what percentage of decks really failed because of nails and what percentage failed because of other design flaws?
Don’t get me wrong, nailing ledgers is a dangerous practice. But according to this study by Michael Morse, Brittney Corwin, Robert Morse, and Andrew Johnson, deck collapses were increasing at a rate of 21% a year between the years of 2000 and 2006. I don’t believe that this rapid rate of increase in the number of deck collapses is being sustained by nailed ledgers. Rather, I think the nailed ledger is merely a symptom of a broader lack of understanding of the nature of the stresses that are being put on the ledger.
Just because a ledger board is fastened with lags does not mean that it can resist frost heave. There are documented cases of lags coming loose. And just because a ledger board is fastened with bolts does not mean that the house frame that it is attached to can support the weight. The authors of the above study point out that many decks put a kind of stress on the house frames that the house frames cannot safely handle. As someone who has seen a massive pressure treated deck attached to a double wide with a ledger board, I can testify to the truth of that statement.
Even if the house can support the weight, all the proper protections against frost heave are taken, and the ledger is properly bolted to the house frame, the ledger board can still fail if it is not properly flashed. Often times, water is channeled in such a way that it pools on and around the ledger board. This causes the ledger board to prematurely rot out which can cause the whole deck to collapse.
I could go on and on. But my main point is that building a deck properly is not a simple thing. People who trivialize the problem of ledger failure as being the work of a few rogue builders who use nails are only perpetuating the problem.
I honestly believe that if people in the trades really knew what they were doing, they would mostly build free standing decks. A free standing deck does not depend on the house frame for any structural support. This means that frost heave is not such a big problem because all of the deck tends to heave at the same time and there is no leveraging effect. More over, I think it is easier to spot structural problems on a free standing deck.
But those of us with good taste will go one step further. We will cease demanding that wood do what it was never meant to do and we will stick to building covered porches and stone patios.