Wax-modified asphalt can be employed in peel-and-stick sheets. In some embodiments, the method includes adding a wax to an asphalt blend. The addition of wax can result in an asphalt having lower viscosity, higher softening point, improved compatibility, and/or stronger adhesion properties. These changes can be achieved in addition to maintaining both low and high temperature stability of the asphalt adhesive. In some embodiments, the wax is made from a recycled plastic.