attic framing for storage /expansive soil
I don't understand your post very well. You state that you cannot put weight directly on the attic floor joists due to expansive soil. So you plan to put flooring up, presumably supported by the joists, but maybe you want to hang the flooring from the roof rafters? Or possibly you are hanging the 2x10 to support the flooring off the walls? I would love to see some pictures, as I am having a very difficult time picturing what you have done and what you propose to do.
I have never heard that you cannot put storage on floor joists because of expansive soil. I have certainly heard about problems in basements, but this is the first time I have heard about attic issues. Perhaps you can fill us in and explain exactly why the expansive soils make it impossible to directly support weight on attic joists.