flush beam decking - joist spacing and post position

[rjlwest]

So I'm going to be putting decking into the garden, attached to the house with a ledger board. 4x4 Posts concreted in, all softwood. I have a good handle on how everything will go in, I'm just not so clear on what joist size to use, how far apart to space the joists, and how many posts I will need.

I've googled and seen loads of tables, but a lot of what I read is designed for post and beam which I'd love to do but can't what with keeping things below 30cm height.

I had marked things out a few months ago as 3250mm (away from the house) x 5400mm (parallel to the house), but I think I'll go smaller than that now.

Ideally someone could tell me something like use 7x2 joists, spaced 1m apart, posts every 1.2m in the direction the boards will run (parallel to house) and 1.2m in the opposite direction to the boards. I suppose that would make it 1.2m joist span, is that right?

 

[rjlwest]

http://www.doityourself.com/stry/proper-spacing-for-floor-joists

Normally, floor joists are spaced 16 inches apart oncenter. This means from the center of one uprightjoist to the center of the next. Given that 2x8s are actually 1-¾ inches wide, it works out to be 14-¼ inches between each joist. With some structures, floor joists are required to be 12 or 24 inches apart on center.

http://www.decks.com/how-to/41/deck-joist-sizing-and-spacing

In general terms, joists spaced 16 inches on center can span 1.5 times in feet their depth in inches. A 2x8 up to 12 feet; 2x10 to 15 feet and 2x12 to 18 feet. The larger the deck, the larger the joists.



so if I use 7x2 thats a 10.5' span which would be fine. surely it would require a few posts along the way? but then if there are posts then the span would surely be measured from one post to another? I'm confused.