All of the following applies to a single family home in a particular town in Connecticut.
In other cities, counties and states, for other types of homes and other types of property, the rules may differ.
On the other hand, in conversations with friends and colleagues and judging the forums, for private houses everywhere everything is about the same.
So, a few facts:
1. The owner has the right to produce construction / repair work of any complexity himself without having licenses, insurance, certificates and the like.
2. Redecorating inside the house (painting, changing plumbing fixtures, lamps, sockets, switches, replacing flooring, laying tiles, replacing interior doors, etc.), as well as routine repairs, are not regulated at all.
3. Everything else (structural changes, electrics, water supply, sewage, heating, ventilation, heat insulation, etc.) requires coordination and several inspections (usually after the execution of rough work and after repair).
In our city, it costs 1.5% of the cost of work. In this case, the inspector becomes also a free consultant.
4. Everything is regulated. That is, literally EVERYTHING: the cross section of wires and pipes, the number and type of sockets and lamps, the height and width of the steps of the stairs, the minimum distance from the toilet to the walls, as they say here, you name it.
All this is described in local SNiP. Moreover, the SNiP in neighboring cities may differ, but usually the International Building Code is taken as one of the latest revisions, and then the state and city may make changes to it.
5. If the repair is not cosmetic, then everything should correspond to the current SNiP. For example, I decided to change the linoleum tile heated in the room between the house and the garage. As a result, it was necessary to open the floor and reinforce the beams (did not pass on the requirements of rigidity for the tile), deepen and warm the “basement”, change the insulation in the walls.
6. If it is impossible to bring something into conformity (for example, the size of the bathroom does not allow to place everything according to the new rules), then you can only update it, but you cannot rebuild it.
7. Often, inspectors close their eyes (and even advise not to follow the letter of the law from and to) to minor violations / deviations. For example, according to the rules, the base of the staircase for an open veranda should be installed on concrete pillars dug to the depth of frost penetration if there are 4 or more steps. I had 4 steps and I was advised not to engage in bullshit and just pour a concrete slab laid on a 25 cm layer of gravel.
As far as possible I will answer questions.