Decks, Patios, Porches and Docks - Building new deck - a few questions

I tore down my existing (not to code) 8x9’ deck, which had a ledger board nailed directly to the siding, and the support posts resting on the driveway/patio below. I’m building a new deck that will have to extend 15.5’ out, in order to clear my driveway/patio underneath, and allow proper footings in the ground. The deck will be 10’ across, and about 7’ off the ground. I am using treated lumber, joist hangers on the ledger, and all screws/bolts - no toenailing.

My city gives very little info on deck building requirements - mostly that it must follow the 2003 International Residential Code. I have looked at the 2006 revision, and cannot find any info pertaining to the questions I have. Could someone more experienced answer some questions?

1. All charts I have seen say it is OK to span a deck over 15.5’ using 2x10 joists spaced 16” apart, using only 2 vertical support posts at the end of the 15.5’. However, every deck I have looked at that spans this far has one additional row of support posts halfway the span of the deck. Am I missing something, or are these decks overbuilt? I can’t add these additional posts properly because of the driveway underneath.

2. With the ledger being a 10’ long 2x10, and the joists spanning out 15.5’, what should the distance between the ledger bolts (½” galvanized through bolts) be if they are staggered as shown?

3. Because of the location of the trunks of the bushes, it is not possible to space the vertical support posts 10’ apart at the corners of the deck. I want to space the posts 8-9’ apart with the beam overhanging by 1-2' only on one side as shown (in other words the beam will not be symmetrical). The deck will not be cantilevered. I can find nothing forbidding this. Is this a commonly accepted practice in a situation like this?

click on thumbnails to enlarge pictures
http://img404.imageshack.us/img404/1933/deck2vo3.th.jpg (http://img404.imageshack.us/my.php?image=deck2vo3.jpg)

http://img404.imageshack.us/img404/2430/deck1zb5.th.jpg (http://img404.imageshack.us/my.php?image=deck1zb5.jpg)

According to this chart, your Beam span is OK.

http://www.decks.com/article40.aspx

According to this calculation, your joist span is too long.

http://www.awc.org/calculators/span/calc/timbercalcstyle.asp

16" OC can go as long as 11"
12" OC can go as 12.9"

here is another one.

This calculator seems to be more lenient. It gives more than 14' for 2"x10" joinst at 16" OC.

If you use 2"x12", it can go to 17'.

http://www.decks.com/Calculators/JoistSpan.aspx

But I do see people have longer span like the second calculator and passed inspection, depending on your location. You 'd better ask your building code enforcement dept. If not short enough, they will deny your application and tell you the correct shape.

Technically and theoritically, your joist span is not too long but you should consider the inplications and consequences of the decision.

Before you dismiss the concept of overbuilding, Will your deck carry a snow / ice load. How will your deck be used.? These are just a few of the questions you should be asking, I'll bet you can think of others.

At the extreme end of the calculations, deflection WILL be an issue. If it is not an issue to you , then there is not a problem. If it is even a remote concern there is not a lot of difference in cost between 2x10's and 2x12's. Over a 10 ft span that amounts to 13 pieces of lumber. The additional cost should be less than $50. That a small price to pay for piece of mind.