I work in the building industry and just like I expect that if something was to happen to me on a worksite that was not my responsibility (and it happens all the time) I or my family would have a form of recourse for any accidents that aren't of my doing, I'd also accord the same level of care to anyone working on my own build.
If you want to role the dice good luck to you but it can very easily come back to bite you on the backside.
i have built 6 of my own homes in various states and used to work in the construction industry and found no need for insurance ,as i am an owner builder i am the person building so why would i take out insurance to cover others ?
the sparkies may be on site for 2 days and the plumbers for 2 days in an average home build but if my site is clean and safe why should i need expensive insurance for such a tiny amount of time my site is occupied by others ?