The removal of water from the roof surface is critical to the success of the system and warranty compliance. The most common method of water removal is through interior roof drains. Proper flashing installation at this point is critical due to the amount of moisture continually flowing through this area.
In Built-up applications; most manufacturers require multiple plies of flashing to overlap at the circumference of the drain opening. BUR systems also typically had a 2-1/2 to 4 pound lead or 16 0z copper flashing (sheet) set over the finished flashing felts and stripped in with a roof mastic. The strip in felts should extend a minimum of 4” to 6” beyond the edge of the flashing sheet.
In Single Ply applications; most manufacturers require that an adhered flashing sheet is set at the circumference of the drain opening. Application should be in accordance with the manufacturers requirements.
The membrane plies, metal plies (if installed) and flashing plies should all extend under the clamping rings.