Low Slope Underlayments & Vapor Retarders

March 16, 2018

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