As you see, my answers differ from others and others may be right on but as far as master insurance, I would not want to have to worry if another party has paid his or her half cost unless of course is in figured into the monthly mortgage payment. Bottom line is you and your family and property need coverage, ask about how to get it, explain the situation and let the trained pro get you "in good hands". I am only an estate agent, and for me to give facts about insurance is an insult to the insurance industry. Trust in me only to say, you need to talk to a professional insurance agent so as not to be misled. be sure to tell the truth abouit the property and the wall, deceit may be used aginst you if you ever need to file a claim and the find out you lied, ..... not good. Good luck, and if you ever need me just call me 978-335-9092.