Retro Pipe Boot is to be used when over the top installation is not an option. Retro Pipe Boot is available in EPDM or Silicone (for high temperature application, use silicone) and includes cable clamp and snap rivets. Retro Pipe Boot has a cut opening that is 20 percent smaller than the pipe outside diameter (OD) to get a compression seal. For Retrofit installations only, a polyurethane sealant must be used on the top where the flashing and pipe meet.