and as a follow up.... is this insurance the responsibility of the homeowner or is it something the GC usually carries.... or both?

Builders Risk Insurance. I got it myself for our house, not really sure if some builders provide the insurance or not.

It's also sometimes called "Fire Insurance". In our case our bank required it for the construction loan and our builder required it in our construction contract. Most places that offer home-owner's insurance also offer this. Usually they'll convert it into a home-owner's policy when construction is complete.

My bank required that we have a Builders Risk policy during the build. It is essentially homewonwers insurnace with added coverage for theft and fire during the construction phase. This policy converted to a regular home insurance policy (and the premium actually dropped by a few hundred dollars per year) after the house was done.

You might also look at adding a substantial liability coverage to the policy which does not cost that much. I think 1 million in coverage cost us around 150 dollars per year extra. You really want this to protect you if someone get's hurt on your site. The builder is supposed to have coverage too - but I think the cost is well worth the extra protection.

As far as stopping theft - it is hard to do when you have raw materials sitting at a job site. The only thing the builder can do is try to install those materials as quickly as possible after delivery.

We have been blessed to have not had any theft so far on our project. My GC has been a builder for over twenty years and his subs have been working for him for the longest of time and are well trusted in this industry around here, so besides the few random delivery guys, and nosy neighbors, there are not many who know about this property being built so I guess that helps out a lot. I couldn't even get scrap material to walk away after leaving it laying there in plain site for a month. I finally had to pay the cornice guys a little extra to pick up all the frame material trash and throw it into a big dumpster.
I still have my prayers out to keep the theft away though.

Our builder and Insurance company call it Cost of Construction Insurance.

HOWEVER - had we put the additional liability on our regular Homeowner's policy BEFORE the house was torn down, that we were told would have sufficed and would have been MUCH less expensive. I really wish someone had told us to do that before we torn it down...

Not sure how it works in the States, but in Canada I had to take out a separate home insurance policy on the new build which includes a 35% surcharge as it is in the building process. Once we move in, it becomes an occupied home policy for the remainder of the period(a year). Inquired about Course of Construction insurance, but in the long run it was a better deal to go this way. Also, one has until the foundations have been poured to take out the policy. Once they have been poured it is too late to apply and there is no coverage for theft from the building site