I have a hay crib wall in my barn about four feet from the exterior wall. The joists were cut so they terminate on the crib wall beam. I wish to remove the crib wall and extend the rafters to the exterior wall. The joists are 2x8. Can I just sister with 2x8's to extend the joists? If so, what should be the minimum overlap? Four Feet? What sort of nailing interval? Preferred nail size? 16d?

Not answering, just adding information:
There are joists which extend from another supporting wall all the way (about 12 feet) to the exterior wall. Such that we have a joist set up of... 12ft, 12ft, 12ft, X12ft, 8ft, 8ft, 12ft, 8ft, 8ft, 12ft, 8ft, 8ft, 12ft, 8ft, 8ft, 12ft,X 12ft, 12ft,12ft...
Between the "X"'s is where the supporting wall is that I wish to remove. Don't know if that is very clear/understandable.

Can you draw this and scan it in?