Low Slope Underlayments & Vapor Retarders

An important element to maximizing roof performance, longevity and building protection on low slope roof systems is the understanding of underlayments and vapor retarders.

Purpose of underlayments:

  • Water barrier (secondary)
  • Thermal insulation barrier
  • Vapor retarder or barrier
  • Air barrier

Types of underlayments:

  • Felt underlayment
  • Synthetic sheet underlayment
  • Self-adhering membrane underlayment

Importance of vapor barriers with metal roofing:

  • Vapor barriers inhibit the passage of warm, moist air into the inner areas of the roof system