An ice and water barrier is required on all roofs.* The barrier may be at least two layers of underlayment cemented together or a self-adhering polymer modified bitumen sheet. There are several manufacturers who make materials specifically for this requirement that are marketed under differing trade names. The ice and water barrier must extend from the edge of the eaves to a point 24 inches inside the warm side of exterior wall line of the building. Existing ice barrier membrane may remain if it is adhered to the roof deck. Ice and water barrier is not required in valleys.
*Exception: Detached accessory buildings (garages)