Weather Resistant/Water Resistive Barriers (WRB) on Walls

August 3, 2018

What Are Weather Resistant/Water Resistive Barriers (WRB)?

  • Air and vapor resistive barrier in wall assemblies
  • Minimizes and controls condensation through vapor transmission
  • Part of the inner leaf of the rain screen wall assembly in design principles
  • Placement is controlled by building use and climate zone
  • In rain screens, it is the last and most critical line of defense against water infiltration

Importance of WRB’s for ATAS

  • Provide architects with sources and product reps for proper selection of WRB’s – WRB network
  • Understand the total wall assembly
  • Be aware of potential integration issues and design concerns for our wall panel systems
  • Typically responsibility lies with the architect and HVAC engineering principal
  • Coordination with structural and HVAC disciplines plus computerized modeling are used to ensure that design and project requirements for WRB’s are met
  • ATAS is not responsible for WRB products nor their placement within wall assemblies

Importance of Weather Resistant/Water Resistive Barriers (WRB)

  • Durable design of air and water resistive barriers is a prime design consideration for achieving energy efficiency, managing humidity, reducing sound transmission and improving indoor environmental quality (IEQ)
  • Minimize and control air/water infiltration through the wall assembly
  • Some WRB’s allow water vapor transmission
  • WRB’s act as waterproofing for walls when installed correctly

Types of Weather Resistant/Water Resistive Barriers (WRB)

  • Self-Adhered Sheet
  • Fluid-Applied Membrane
  • Closed Cell, Medium Density Spray Polyurethane Foam
  • Factory-Bonded Membranes to Sheathing
  • Boardstock – Rigid Cellular Thermax Insulation Board
  • Mechanically Attached Flexible Sheet

ABAA Model Specs Currently in Development:

  • Adhesive Backed Commercial Building Wrap

Limitations of Weather Resistant/Water Resistive Barriers (WRB)

  • Air and water control are often two separate entities requiring different solutions based upon WRB selected
  • Not all vapor retarders are durable enough to resist air movement, and not all air barriers resist vapor drive
  • Improper placement or improper type of WRB can lead to trapping moisture within or across wall cavities and can result in condensation problems
  • Inadequate detailing almost always results in failure