The addition of tape to dog bone specimens of built-up roofing membranes consisting of asphalt-saturated organic, asbestos, and fiberglass, and coal-tar-saturated organic felts (no roof insulation) indicates that the tensile strength is increased from 23 to 73 lb/in. The breaking strain of some membranes increased while decreasing in others where tape was added. The load-strain modulus increased with the addition of tape to the dog bone specimens except for coal tar felts at -4 F. Test temperatures were 73, 32, and -4 F. Tests of built-up roofing specimens consisting of 2 by 4 ft samples of asphalt-saturated organic, asbestos, and glass fiber, and coal-tar-saturated organic felts over mineral aggregate, fibrous glass, wood fiber, or urethane roof insulations, indicate that the addition of tape at the joint increased the breaking strength except for fiberboard roof insulation and asphalt-saturated organic felts. The break strain and the load-strain modulus increased for some specimens while decreasing for others. Test temperatures were 32 and -4 F. The properties of the tape used may not provide for ultimate performance of all membrane systems. Some roof insulations are more suited to take advantage of the increased break strength when tape is used. Bitumen characteristics appear to dominate the behavior at low temperatures. The data are derived from a limited number of tests, and continued research is needed. Roof tape properly installed retains the ply bitumen in the membrane system, resists moisture ingress into the felts, and increases the membrane breaking strength.