I haven't thought about the implications of having one out of three joists different from the others, nor about the detail you've described for notching the 2x10s over the sills. But I can tell you how to use the Deflecto to model your composite 2x8 + 2x10 joists:
First model each one separately, I'll assume Unknown Wood in Good Condition and modern dimensions, and I'll round the span up to 15'6" to be conservative. For 2x8 at 12" o.c. I get L/155. For 2x10 at 12" o.c. I get L/298.
For the composite, you just add the denominators, so you're at L/453 (at least for those 2 out of 3 joists). The reason this works is as follows: L/155 means that, say 155/1000 times the standard load would deflect the joist L/1000. And L/298 means that 298/1000 times the standard load would deflect that joist L/1000.
If you are going to deflect both joists simultaneously to L/1000, you'd need to add those loads, in other words 453/1000 times the standard load. Which means the standard load deflects the composite joist L/453. [The use of the factor 1/1000 was arbitrary, it's just to illustrate the point and to keep the loads involved in the linear region.]
Cheers, Wayne
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Wayne
