Structral Question
 

I am looking for the formula for the different sized boards for the joist (ex. 2 X 6, 2X 10)

The formula that I am looking for is how to calculate the maximum span I can run my floor joist using a deflection of L/360. and I am also looking for the spacing between joist. I am not sure what a good pounds per square foot would be, I am not putting a hot tub or anything on the deck.

I know there are places on line that I can enter the type of wood I am using but in the size of board I want to use and specify the spacing that I would like to use and it will calculate the span that I should not exceed. But I am looking for the formula that is used to arrive at that answer if anyone can help me out.

you will need or should probably go to an engineering site to see if that is available. Might try a university also
steve scholl
www.thedeckbarn.com
www.killerdecks.com

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I think for this you have to look for a engineering website..

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http://www.thedeckbarn.com/howto-buildadeck.aspx Here is a how to that will give you the formulas you are looking for. There were made by The American Wood Coulnci.
www,thedeckbarn.coml