Question: what is the difference between f channel and j channel?
Answer: The F-channel, as shown in Figure 4, provides nailing or stapling in the same plain as the soffit material. The J-channel, as shown in Figure 5, provides nailing perpendicular to the soffit. ... Always allow a 1/4 inch expansion on both ends of the piece of soffit. In colder climates it is best to allow 5/16 inch.