A roof system comprising a substrate and thermoplastic membrane adhered to the substrate, where the thermoplastic membrane is characterized, prior to being adhered to the substrate, by a stiffness represented by a flexural modulus of less than 90 MPa, or by a Taber stiffness of less than 15, or by a Shore D hardness of less than 40, or by a combination of a flexural modulus of less than 90 MPa, a Taber stiffness of less than 15, and a Shore D hardness of less than 40.