An inspector needs to be on the lookout for structural problems with cantilevered decks. That is especially true here in the northwest where we have so much rain.

Do you know what a cantilever is? Here is a pretty good photo that I took at a recent inspection.

See that beam: Dark on the inside and white outside where it supports an upper deck. Notice how green that beam is at the exposed outside section. That is a big problem with this design. As the wood is exposed to rain on the outside, rot forms and that will travel right down the beam. Before long you have a deck that is seriously weakened, likely to be unsafe, and you also have a repair job that takes some doing to fix -- especially if the decay gets back into the exterior wall.

The cantilever design might work great in some climates, but it creates many problems in the Pacific Northwest.

Thanks for stopping by,

Steven L. Smith

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5 Comments on The Problem With A Cantilevered Deck

NOV
05

Additionally the length of the cantilever should not exceed 1/3 of the total length of the beam (or joist as the case may be).

In other words, if a beam is cantilevered 6' out from the supporting wall the beam must have a total length of AT LEAST 18' with a minimum of 12' extending into and secured to the building structure. And the beam still must be sized for the load and span.

1:20am • #1
574,044 Points 18 Featured Posts Outside Blog

Bruce,

That is true enough. The old 1/3 rule. In this case the beams ran from one end of the house to another which is often the case here. But, when it rots away, well then it is a big problem.

1:28am • #2

Beam rots away.  Water gets into the wall structure.  Often bumps occur in the interior floor where the cantilevered piece attaches to the house structure.  Cantilevered decks are a bad idea.

9:33am • #3
103,206 Points

Hello Steve, I agree it rains here (sometimes) and is often damp for extended periods.  I too have seen way too many of these decks in older homes, and they look like a real chore to replace and update correctly.  Thanks!  John

6:56pm • #5

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Steven L. Smith, Bellingham, Wa. Home Inspector

Bellingham, WA

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King of the House Home Inspection, Inc

Address: Bellingham, Ferndale, Lynden, Blaine, Sumas, Nooksack, Lake Whatcom, Lake Samish, Anacortes, Mount Vernon, Whatcom County, Bellingham, WA, 98225

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