Gary: In the local 2015 Annual Homeless Point in Time Count, they counted 1,473 people. (This is known to be a considerable undercount since the count is done at night by volunteers and the camping ban forces the homeless to hide.) Of the 1,473, 206 were considered to have "chronic alcohol/substance abuse issues". That's 14 percent. 
http://www.lanecounty.org/Departments/HHS/HSC/Documents/PIT_COUNT_Highlights_2015.pdf

So I can't really see addiction as a "leading" cause of homelessness. It might be for the 14 percent, but correlation does not imply causation. It's probably a chicken and egg situation, a positive feedback cycle. I wonder what percentage of the housed have "chronic alcohol/substance abuse issues"?