The codes should only apply to Basic structural requirements concerning framing (load path to foundation and structual integrity of the framing; bracing, etc.); and Basic installation requirements for installation of electrical, plumbing, and mechanical requirements (protection of the installation, correct slope, and support of installed distribution systems).
If they want requirements above this it should be per manufacturer's installation instructions; with a signed statement of compliance of those instructions by the contractor; with heavy fines for non-compliance. My idea of heavy fines is forfeiture of the total payment for the job contracted. Having to do the work for free; and, then reinstalling at the contractors expense; should interest them in training their employees and hiring a knowledgeable supervisor to see that the work is done correctly.
We don't have enough knowledgeable code inspectors to do the job; and, that problem is not even being addressed or considered.
Hey, I've gone Platinum with 1,000 posts. I hope some of those posts were useful.
Uncle Bob