Above Sheathing Ventilation (ASV) – The Perfect Roof

September 11, 2020

Above-Sheathing Ventilation (ASV) is achieved by having continuous air flow between the roof sheathing or wall assembly and the metal panel system. ASV creates energy savings by reducing
air-conditioning costs in the summer and adding insulation value during the winter as proven by studies and testing performance sponsored by Metal Construction Association (MCA) at Oakridge National Lab. ASV also minimizes the effect of condensation between the roof layers and wall assemblies.

Basics of Control Layers

Rain control layer

  • Resists environmental elements
  • Provides UV protection to assembly
  • Provides aesthetics

Air space control layer

  • Provides drying of overall assembly through air flow
  • Provides thermal comfort
  • Minimizes effects of condensation within control layers
  • Reduces chances of any mold build up that could lead to wood distortion or metal corrosion
  • Helps prevent ice damming

Thermal control layer

  • Poly Iso rigid board
  • Extruded (XPS)
  • Expanded (EPS)

Air control layer

  • Air and vapor impermeable barrier
    • Eliminates air which can also carry water vapor
  • Air permeable barriers
    • Allows air vapor/moisture through

Structural deck assembly

  • Metal deck
    • Steel b-decking
    • Open steel framing
  • Wood/plywood substrate
    • Plywood/OSB
    • SIPS (structurally insulated panel)
  • Exterior fire-resistant board