A roof expansion joint, EMSEAL RoofJoint is a patented dual-seal, double-flanged, extruded thermoplastic rubber system for sealing expansion joints in roofs. Watertightness is achieved through positive integration with the roofing membrane and a purpose-designed system for transitioning between the joint in the roof and joints in walls. The waterproofing element of most other roof expansion joints is a looped membrane. The loop either hangs down into the joint or is humped up by means of a foam backing. Either way, looped membranes don't work well at the transition from the roof joint to wall joints and feature only one level of sealing.