What does the term "perms" measure in building materials?

The term "perms" refers to the measurement of vapor permeability in building materials. Vapor permeability is an important property that indicates how easily water vapor can pass through a material. This measurement is crucial for assessing moisture control within building assemblies, as it helps to prevent problems related to condensation and mold growth.

By understanding the vapor permeability of various building materials, architects and builders can select appropriate materials and design strategies that facilitate proper moisture management, contributing to the overall durability and energy efficiency of the building. This is especially relevant in environments where humidity levels fluctuate significantly.

Thermal resistance, sound insulation capability, and fire resistance are also important properties of building materials but are not measured in "perms." These properties serve different functions in terms of energy efficiency, acoustics, and safety, respectively, but they do not relate to the movement of water vapor. Understanding vapor permeability and its measurement helps in ensuring effective performance of the building envelope in various environmental conditions.