One of the "joys" of living in the USA is every municipality has a different building code enforcement scheme, so WRT "As my structure is too small to require

One of the "joys" of living in the USA is every municipality has a different building code enforcement scheme, so WRT "As my structure is too small to require permits or inspections, I don't need to abide by silly bits of code. I'm not concerned with room-to-room fire spread resistance in a single room office. The 1/2" plywood goes up similarly to the foamboard ..." Humorously code where I live is 3/4 ply counts as an actual firestop! If he had installed a slightly different product he would have been legal. Note that my state is not exactly a victim of droughts and wildfires and your state's codes are correspondingly different. Likewise home insurance is regulated at state level and its important to understand the insurance coverage difference (if any) between built to code vs built under a permit. Also insurability. The city might not be able to legally knock down a little shed, but if the insurance guy refuses to insure the property thats almost as bad. There is one interesting illegal problem in that if you do outright illegal work at the same quality level or better than a pro, then if someone bad ever happens (and why would it?) then its going to be extremely easy to pencil whip it as grandfathered or unrelated. On the other hand once you get into the habit of shoddy workmanship then inevitably 1) You're gonna be involved in an unfortunate claim 2) its gonna be really hard to claim its grandfathered work.