Builder's Risk is what you're looking for, is easy to obtain, and is sold in 6 or 12 month increments. Premiums are based on initial value, repairs needed, and ARV... I generally pay 700ish for a 6 month policy. It's a big hit, but like any other insurance policy, it sucks to pay for something you're "not using", but if you ever need it, it will be catastrophic to not have it. I figure it's the cost of doing business since if my 50k-150k house burns down with no coverage on it, I could effectively be out of business. I price it into my rehab budget from the outset.
My company also carries a liability policy which gets each property added to it when when we purchase and removed when we sell (no change in premium). Your liability picture will be specific to your company and operations, so you'll need to discuss that with an agent.
PM me if you need an agent in NH, I have one I'd recommend. Not local to you, but in NH and everything can be done by phone/email anyway.
