How in the heck should I plan my deck?

February 4, 2007 10:23 AM

Where can I find guidelines or software that will help me design a rectangular, free-standing deck with cantilevers?

I have looked at lots of books and googled around a bit. All of the guidelines I have seen are for attached decks and don't cover cantilevers.

I'd like to be able to optimize the deck for minimum number of post holes and minimum cost.

The deck will be about 15' by 24'. For aesthetic reasons, the beams will be along the longer dimension. The beams and joists will have a 2' cantilever on both ends. The structural elements will be pressure treated pine and the decking will be Cedar.

posted by Could it be, El Guapo ... to Home & Garden (1 answer total)

Best answer: To get the longest spans between posts you could use glue laminated beams. You would require two 24-foot beams and four posts (which could also be laminated). The beam would span two posts 20 feet apart with 2-foot overhangs on each end. The two beams would be 11 feet apart. The joists could be 2x8 but 2x10 would be better. They would overhang 2 feet over the beams. Don't worry about the overhangs. Any beam that can handle the 20 foot span will have no problem handling the 2-foot overhangs. The same for the joists. If they can handle the span, the overhangs are not a problem.

Your most important decision will be determining the size of beams and posts required. You can find a lot of information at glulambeams.org. Free registration is required.

Keep in mind that the strength of a beam depends more on the depth of the beam rather than the thickness of the beam. The design for a free standing deck is not much different than for one attached to a house. In one case half the load is carried by the house and half by the beam. In the freestanding case, half the load is carried by each beam. The one thing to consider is the need for more diagonal bracing on the posts to prevent swaying since you don't have a solid attachment to the house.

You might also consider using composite decking rather than cedar. For example Trex decking is made from wood chips and recycled plastic. It looks great, never splits or splinters and never requires staining or treatment. It also saves trees.
posted by JackFlash at 1:42 PM on February 4, 2007