Is Your 2nd Story Deck Safe?

Submitted by KimChristensen on Mon, 07/22/2013 - 14:53

Beginning around the turn of this century, building practices began to change regarding deck construction. Most older decks, prior to about 2000, often were built to lesser standards than those that are required today. There have been many instances through the years of decks collapsing, causing severe injuries and deaths. In fact, in just the past 10 years there have been thousands of reported injuries and more than 20 deaths as the result of deck collapses. If you have a deck and it's only a foot off the ground then it's not as big of a deal. But if you have a second story deck and it collapses while you and your guests are on it, then it's a huge problem.

 If you have a balcony that is supported by cantilevered joists (joists that start well inside the house and continue out to the deck), and as long as the length at the deck portion of the joist is not more than one third (two thirds of the joist is inside the house), then this is considered a valid practice. The problem comes when the deck was constructed without cantilevered joists and is simply attached to the house where the two meet. There are two main problems that can occur at this attachment point. Improper fastening methods and water intrusion.

There should be a treated or decay resistant  ledger board (2" x 8" minimum) that attaches the deck to the house. Also, this ledger board should never be attached directly to the house wall cladding. This includes brick, stucco, or any other material. The wall cladding should be cut at this point and sit above the horizontal ledger board. Nails are not sufficient to attach the ledger board to the house. Galvanized steel or stainless steel 1/2" bolts or lag screws are the usual minimum size that should be used, and they should go through the house sheathing and attach to a band or rim board in the house. Special hardware such as Simpson Strong- Ties are also very helpful. These brackets are designed just for this purpose and greatly increase the horizontal strength of the attachment. This structural attachment is important because it must carry the vertical weight load of the deck and the people who will be on it, as well as the horizontal force that wants to pull the deck out away from the house. If the attachment can't withstand these forces, deck collapse will result.

As for water intrusion at the attachment point, it's very important to have in place the proper systems to keep water away from it. If water regularly penetrates to the ledger board and the attachment hardware, rotting and corrosion will eventually compromise their structural integrity. To achieve this goal, metal flashing (usually galvanized steel) should be seen tucked behind the bottom of the wall cladding and extending over the ledger board. This will help drain the water away and protect the area.

Another problem that has developed is failure of the hardware attaching the deck to the house. This hardware can sometimes corrode fairly quickly from the chemicals that are used in pressure treated lumber. Particularly in decks built from about 2004 to 2007 when the chemicals ACQ and CBA began to be used to treat wood. To resist this corrosion, galvanized hardware should be of the hot-dipped type and not the thinner coatings like electro-galvanized or mechanical plated. Aluminum should never be used, and the mixing of different types (for example, using galvanized and stainless steel together) should not be done.

Finally, all guard rails and handrails should be properly constructed and solid. If you have a two story deck, or are thinking of buying a house that has one, be smart, and have it inspected by a knowledgeble home inspector who knows how to look for the previously mentioned concerns. Decks can be wonderful and relaxing places to be, but a deck collapse would be a life changing event that no one should ever have to go through. For more information, visit Simpson Strong-Ties at http://www.strongtie.com/deckcenter/index.html?source=topnav# , or the American Wood Council at awc.org/codes/dcaindex.html --- Kim Christensen

Submitted by KimChristensen on Mon, 07/22/2013 - 14:53