Spot Foundation & Floor Joist Strength

[pioneergal]

Ok .....DH and I have another idea.

We first thought of digging the 8x8x16 spot footings 8 inches deep  and filling the holes with concrete and then stacking the cement blocks ontop of the footings.
John and a few others commented that this should not be a problem.
 
What if we dug the 8x8x16 footings and filled the 8 inch holes with gravel and then placed a 16x16x2 pad ontop of the gravel and then stacked the blocks?

Also, we are planning to use 2x8x16 floor joist on 16'' centers with support every8 feet.
Will this span be too much for this size joist?

[rwalter]

If you have a beam supporting the joists at 8 foot intervals you'll be fine. You can check the maximum span a joist will cover by using a span table. Here is link to one of the best span tables that I have found. Building codes for first floor living areas normally require that you meet a 40/10 Live/Dead load with a minimum L360 deflection. In some areas of the country they may allow a 30/10 loads with L360 for second floor sleeping areas. (Not in NY they require 40/10 everywhere). As John has pointed out in many of his post previously when you get longer spans, > 15 feet  you may want to use an L480 or higher deflection value to keep your floors stiff and eliminate the bounce you would possible get from a lower deflection value.

Span calculator - short URL -GK
http://simurl.com/varmen
 
I'd also ask you local building inspector what the codes are for loads on floor joists. Most building inspectors are a great source of information and very helpful.  As for your foundation that varies also depending on you location and building codes. Again I'd check with your local building inspector.

[jraabe]

In most cases a "rubble trench" footing will serve as well as a poured concrete footer - especially for spot footings like you would have for a post and pier foundation. Make sure water will have a way to drain away from the footer or you can have frost heave problems.

The exception would be if you need to anchor into the footing for things like hurricane straps to provide uplift resistance.