It took me a long time to realize that most of the contractors we hire don't read books or journals about how to do their work.
Most of our contractors do what they've learned from colleagues, friends and family, and what they've invented on their own. The best of them know local code. Only a very few seem to read books and magazines related to their craft. (Some of which, of course, are nonsense -- this is not a peer reviewed literature.)
This means that contractors practices can be very far from best practices. A home owner can't hire a good contractor until they study books and journals first . Then it's possible to have an informed conversation, and ask a contractor to exlain their (often correct) deviation from what's written.
This should not have surprised me. North American trained physicians have very strong native study skills and strong legal and strong professional incentives to learn and adopt best practices. But we struggle to do that. Why should contractors, who are not selected for academic excellence, be any different?
 Yes, paper. This domain is very poorly represented online.