The Danger of Wood-Framed Cantilevered Balconies: Part 1

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This is the beginning of our Three Part series of Balcony Risks in light of Berkely Balcony Collapse. The other articles in the series is Part 2: HIdden Dangers of Wood-Framed Cantilevered Balconies and Part 3: Preventing Balcony Collapse.

A few of my recent construction defect cases have impressed me with just how dangerous wood-framed cantilevered balconies can be.   

What makes these wood-frame balconies so dangerous? 

Quite simply, wood can fail without warning. By contrast, with concrete or steel structures, deflection is generally observable as the deck begins to fail, providing a warning that something is wrong and allowing time for corrective action. With wood, you often will not know anything is wrong until it’s too late. 

Here is what is happening: The mode of failure on wood-framed cantilevered balconies is usually a result of water intrusion at the deck-to-wall transition, which generally includes the door threshold. This area is clearly the most complicated intersection of materials on a typical deck construction. The water intrusion typically makes its way into the sheeting at breeches in the sheet metal flashing and deck waterproofing. Deck sheeting, usually consisting of plywood or Oriented Strand Board (OSB), holds moisture in contact with the top of the wood structural joists, with rot starting at the top of the joist and working its way down into the cross-section of the joist, adjacent to the outer wall of the structure. The mode of failure that I have outlined just happens to occur at the exact location where the most critical structural members (the joists) have the most structural load (the top cord).  

Failure of these joists usually occurs abruptly, and on cantilevered balconies, there is no secondary system to pick up the load when they do fail. Unfortunately, failure can be fatal when the cantilevered deck drops like a hinged trapdoor under the load of people standing on the deck.

So, how do we avoid these disasters in the future?  Watch for Part 2 of this story in our spring newsletter, which will look at regulation changes coming and focus on simple yet effective solutions for avoiding catastrophe. 

To learn more about inspections of wood-framed cantilevered balconies and Xpera’s other quality assurance services, contact Steve Grimes at or call (858) 436-7770.  

Topics: Waterproofing Systems, FS, Ted Bumgardner, Construction Forensics, QA, Balcony, Publications


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