how many 2x8,s do i need
 

how many 2x8,s do i need
by the spanish practice your setup seems to need quite scarce, say 7 independently 2x8 in (all continuous from support to support) collaborating to take 12 ft of floor in a 16 ft span. if you can it will be more efficient to use members of more depth. you would be initally taking 1.4 tonne/m by the spanish evaluation, and to take the same with only 8" deep in the new 16 ft span would take a width of 28 in or 14 such 2x8 members, for a central deflection of a bit less than 1". the practice in your area may be less stringent. in any case, the recommendation of using more depth i see becomes from the evaluation quite clear.
er, the named deflection is at the end of the life of the structure. a divisor to initial stiffness of 5 has been uses to this purpose, so initial deflection will be scarcely noticeable.