The use of a retraining batten on the underlay laps means the use of an extra batten, or the lap length increasing to coincide with a planned batten position reducing the coverage rate of the underlay.
Using a taped lap system, none of this is necessary and the wind load and zone performance is often improved. Separate lap tap tapes can be more difficult and time consuming to use. They have to be applied carefully to the underlay that must be clean, dry and free from all dust and debris. For this reason, roof underlays with an integral lap tape are recommended for speed, ease of use and reliability.
