Over the years I have loved collecting deck failure stories from all over. This one was brought to my attention in the latest version of the Journal of Light Home Construction August 2004 issue. I have got to place it in my all time favorite lists of Ignorance in Action awards.
COLLAPSE OF OVERLOADED DECK TEACHES USEFUL LESSONS
Standard residential decks aren't capable of supporting heavy objects like pools
Independence Day weekend came and went this year without any reports of fatal catastrophes involving outdoor wood decks or porches. But as happens every summer, a few smaller deck failures have made the news, including one case in Hughsonville, N.Y., that luckily did not hurt anyone, but did teach a valuable lesson.
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| This five-year-old deck collapsed as a result of severe overloading. Decks built to code should be able to carry a 40-psf load; a pool placed on this deck weighed an estimated 180 psf. |
Built in 1999, the second-story deck gave way suddenly under the weight of a large plastic swimming pool. "The lady was inside putting swimming trunks on the kids when she heard a boom, and when she looked outside the whole deck was gone," says town firefighter and police officer Mark Liebermann. "These people just didn't understand that you can't put a freakin' swimming pool on top of a deck."
This was not a little wading pool, says Leibermann: "It was about the same size as a tank we have for filling fire trucks down at the station, and that holds 2,500 gallons. It covered the whole deck except for about two joist widths in front of the door, and it had about 3 feet of water in it."
While some deck failures are clearly the result of under-designed or poorly built structures, this case involved obvious overloading. And because the load that caused the failure was an evenly distributed mass of a uniform material (water), its magnitude can be estimated without the uncertainty involved when the live load consists of people at a party. A cubic foot of water weighs just over 62 pounds, so 3 feet of water in a pool would have loaded the deck to approximately 180 psf, more than four times the code-allowable 40-psf load.
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| Seemingly undersized joist hangers still supported the joist ends at the house ledger after the collapse. At the other end, there were no hangers. The joists pulled away from an outer rim member, which appeared to have snapped in half. |
In any case, the 40-psf allowable live load is intended to account for the weight of people, and in no way includes any allowance for pools or other heavy objects. Engineer Frank Woeste, professor emeritus at Virginia Tech, comments: "In theory, a code-conforming deck should safely support 7.7 inches of water in a kiddie pool, neglecting the weight of small children in it. But without professional verification, you can't assume the deck is built to code. Even if the deck were designed and built to support the code-prescribed 40-psf live load, deck components can deteriorate in service and not have the strength and safety factor of the original construction. Heavy objects, such as water-filled kiddie pools, should not be used on residential decks unless the design specifically addressed the maximum weight of the object in addition to the 40 psf from the residential code used for the ordinary occupant live load."
I did a lot more research and was able to locate the original report of this story on the Hughsonville, NY Fire Department website. Here is what they reported...
http://www.hfd45.org/asper.htm
DECK COLLAPSE
JUNE 1, 2004
At about 1:30 PM, Town of Wappinger Fire Inspector Mark Liebermann responded to a report of a collapsed deck at 2 Asper Lane. The approximately 16x20 deck was the only entry way to the second floor apartment. Upon arrival it was observed that only two joists were holding the remainder of the deck to the structure, The apartment was occupied by a family with three young children. The Hughsonville Fire Department was requested to the scene to shore up the deck and assist in evacuating the occupants. The occupants installed an above ground swimming pool on the deck and the deck failed. The structure was ordered to be removed and the apartment posted as uninhabitable until a new deck can be constructed. The occupants were provided temporary housing by the American Red Cross.
