In our current place, we moved the main access door from going into the kitchen, to entering an old laundry room converted to a mud room. In order to do so, the front door was moved over about 4', and off the existing concrete patio. The bottom of the door sill is ~11 1/2" above the existing slab, and ~12" above grade. You can see a plan view of the existing concrete patio and proposed deck below.
The plan is to make a 10'x12' deck. Why so big for an entry way? Well, it is next to the kitchen, and it would be a great spot to grill. Also, I plan on building a bench or two on the deck for kids to take off shoes, boots, etc.. before entering the house.
Since the deck is so low to the ground, I plan on building it directly on the slab, and having it free-standing (i.e.- not connected to the house, thus no ledger board). By "directly on the slab" I mean to also shim it up, say, 1/2" to allow for circulation and water flow. I plan on using 12' 2x8 joists, spaced at 12". First question- does this all seem like a sane idea?
For my second question- obviously this deck will hang over an area where there is no concrete slab. Would it be enough to place an 8" diameter, 4'deep footer at the two outside corners and in the middle of the 12' span, one joist in from the outside, at the same level as the slab? (see dotted circles in the drawing).
Any other thoughts? Am I out of my mind?