What is the proper way to apply subflooring to floor joist's when they change direction. Do you continue with the same pattern or do you change the direction of the subfloor pattern to match the joist change? And if you do what is the proper way to make the change?

subfloor must run perpendicular to the joists

Excellence is its own reward!

Of interest, we just discussed this issue. According to an APA spokesperson, subflooring (and here we assume plywood) generally runs perpendicular to the joist direction. This is the best structural situation. However, where there is a change in joist direction, for instance at a cantilevered situation where there are different forces being applied to the supporting joists or beams, for architectural reasons, it is best to have the plywood subflooring span over the change in joist direction. By spanning over the change, one reduces any potential difference in deflection of the adjacent joists. However, the unsupported edges of the plywood that would normally fall on a joist must then be supported by additional blocking.

That is true. Adding blocking maintains the rule of running perpendicular by supporting the weak grain .

I would not limt the discussion to plywood though. Olywood has suffered a decrease in quality over the past twenty years as a general rule and delaminations on the job have become more common. Meanwhile replacement products such as Huber's Advantec have come to replace it and perform much better than either typical plywood or the previous generation of OSB type sheathing materials.

Excellence is its own reward!