Friday, May 11, 2012

Deck Design Do's and Don'ts: Part 3

Sawn lumber, unless protected, is highly susceptible to shrinkage, swelling, twisting, and bending when exposed to moisture.   For an outdoor deck, lumber is exposed to rain and changes in humidity, the latter of which can be a nightmare in Alabama.  The deck in the picture below shows signs of joist failure.  One saving grace for the deck is the fact that the two test stations that have toppled over are constructed of thin, hollow metal and are much lighter than they may appear.  


The second picture, shown below, shows how the joists are being held up by the deck.  The 1x ledger board used to support the joists is still in place.  Unfortuntaly, the beam has rotated away from the deck, allowing the ledger to slide out from under the joists.  The beam's rotation and deflection were exacerbated by the effects of weather exposure.  The few nails that connected the beam to the joists were nailed from the beam and into the end grain of the joist, leaving very little resistance to lateral separation.  The beam's lack of resistance to moving laterally allowed the effects of loading and weather to combine; ultimately causing failure of the deck without failure of the beam or joists.   



Small changes in the construction of the above deck, such as toe nails or joist hangers, could have made a big impact on the decks performance.  Thankfully, the employees working at the facility were unharmed. 

Statistically, deck collapses are responsible for more people being injured or killed than any other part of their residence.  Taking the time to consider low cost, high impact changes in all aspects of construction should be at the forefront of every builder.   

Click here for Deck Design Do's and Don'ts Part 2 and here for Part 1. 

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