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msj67 09-08-2009 08:17 AM

Joist size recommendation?
I'm building a new deck and can't decide on the size of the joists. The deck will be 18 feet wide and 12 feet deep, and will be built with pressure treated pine. The joists will be 16 inches O.C. and the span will be approximately 11.5 feet from the house to the support posts. Because of an existing structure below the deck, I can't place the support posts closer to the house. I understand that 2x8 joists at 16 O.C. can span a little more than 12 feet, but I'm thinking I should go with 2x10 joists at 16 O.C. What do you think, should I go with the 2x10 joists for this deck? I would hate to go too small and regret the decision later. Thanks in advance!

msj67 09-08-2009 08:32 AM

I should add to my earlier post that the deck will be approximately 9 feet off the ground.

thedeckbarn 01-09-2010 05:21 PM

2x10 will do the job fine. Whether you are 16" o.c. or not has a lot more to do with the decking than joist span. To simply change to 12" oc because you will get a greater span due to what the table says should tell you that you are working near the limits of the lumber any ways. The span tables are for the max. allowed, not the limits to which you should be working.
You can find all the joist span and info on how to properly build a deck on my web site There is a section devoted to it. The section was written by The American Wood Council. Which you could find by going to google and type in AWC.
Certain composites require 12" oc joist. When we build we always frame 12" oc because the difference is only 2-3 boards on a 16' wide deck. That price even using 2x10 wold be $40.00. I find that relatively inexpensive to know it is a good job
steve scholl

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