A: Technically, no, such an agreement is not "required." However, you are smart to avoid putting all of your faith in a pre-existing friendship (for the benefit of ownership and the friendship). A strong agreement should cover things such as use and payment of rent between the co-owners, duties of repair, payment of expenses/taxes, the sale of the property, assignment of rights, survivability, and any other thing you can think of that might occur during the time you own the property.
