decking question

greetings, i am building a deck that will be 17 feet wide by 9 foot deep. i will use 4x4's dug three feet into the ground, with a bag a cement in each hole. my question is how much support(4x4)will i need for the 17 foot span? obviously one 4x4 on each end but will one 4x4 centered be enough or should i break the 17 into thirds? so 4 columns instead of three? cj
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it depends on how big your rim joists or outside girders are. or if you double them. I'm working on a deck now, that is 22' by 14' and we used treated 2" x 8", doubled. then the rim joists are through bolted(galvanized 10" bolts), and just for kicks we installed support blocks under the joists on the posts. On the 22' side, there are 4 posts (including the corner). All joists in between are attached with hangars and approved nails. Don't use deck screws to attach the joists to the posts and expect that to be good enough. No shear strength. hth perry
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Better is not to have 4x4 posts below ground as they will rot quicker but have them attached by metal bracket with concrete above ground by 1" or so.
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You've got your whole project bassackwards. Take a breath here and do some logical planning.
1) You will have to have a building permit in most communities. 2) A permit requires a set of plans with specifications such as dimensions and materials. 3) The plans must meet the city building codes. 4) Many box stores have free deck planning services. Take advantage of it. 5) Once you have applied for and received your permit, all your questions will probably have been answered. 6) If you need clarification of any details, the inspectors in the office can be amazingly helpful...all you have to do is to ask and then listen.
Common sense says that reinventing the wheel is the curse of the ignorant. Find out where the knowledge and expertise is in your area and go for it. Good luck.
Joe
Unless you have a degree in civil engineering and lots of construction experience it makes no sense at all to wade into any large project. .
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Time and time again, every time I poke my nose into one of these forums I see posts that are the equivalent of asking "how long is a piece of string". often the poster has made up his mind before he asks a question.
To the OP and just about everybody else who cares to listen, the post by Joe should be read, read again and probably copied so that you don't forget. After 50 years in the game I could not have put it better. He is spot on. Just in case you want to check me out look at my brief page on decks. http://www.builderbill-diy-help.com/deck.html
To reinforce what Joe has said, I am this afternoon going to look at a house with a structural engineer and a real estate person. The place has had illegal additions to it, the owner wants to bring these up to the current standard. The reason for this? The owner wants to sell but has only had offers up to $320,000. Similar houses in her street have sold for over $400,000.
It would have cost her a fraction of the cost she is faced with now, to do it right in the first place.
Cheers Bill.
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