Cities can modify their codes any time, making you change things that used to be legal when it was built.

What is vastly different between US and other developed country area) the tendency of suing between people or enterprise, this create almost every industry has noticeable legal fee/lawyer fee when they conducted a business and punish the consumer at the end.b) the power of private enterprise to create regulation and influencing goverment decision which at the end creates oligopoly structures which dominate how the government react to particular industry (well you can say lobbyst).c) the dependencies to technology (without good understanding of its technology)d) the overcomplicated tax and building code , which at the end creates more profit  to big corporation only.These are the fair point in my own thinking why commision is high , especially #2, it's just the "realtor cartel" push that agenda to public and gov ; and since gov is part of private enterprise too, they just accept it LOLAmerica is one big giant corporation executed by Exxon,Apple,Microsoft, Blackrock, Blackstone, Shell , Lockheed and AIG  whole industrial powerhouse LOL :-) what you see in TV if they seems fighting is just a drama lol

Oftentimes they will not meet new code requirements.

However, there is a commercial duct running behind my bedroom wall that I strongly suspect is being used in violation of the building code.

@Ian BruesehoffGive them like $25,000 for their guru course and they give you the super secret code

Internal Revenue Code Section 1031.

I can't imagine changing codes every guest.  

I am curious though: if you locate a good property, and by good I mean (as an example)  3br 2 ba SFH, in a hot zip code, with plenty of comps to figure ARV, at 70% of ARV minus well estimated repair costs and reasonable assignment fee, and then offer it as is to investors in current market, how difficult would it be to sell it if your trusted/connected buyers didn't want to buy it?

I believe that under a standard title insurance policy, building code matters, zoning and other governmental restriction on the use of the property are excluded from coverage so unless you purchased an extended form title policy there probably is no coverage, but it never hurts to submit a claim. 

I was considering getting just SIP panels from china, and reputed SIP panel companies in china says they do not ship electricals and plumbing as local codes monitor them closely.