Vapor Barrier vs Vapor Retarder vs Moisture Barrier vs Air Barrier

Follow

Claire Fontaine

October 11, 2024 14:15

Hi there, Could someone please explain the difference between vapor barriers, vapor retarders, and moisture barriers? Is a vapor barrier a type of moisture barrier? Is a vapor retarder a type of vapor barrier? Are vapor barriers permeable to air and air barriers are not? In the eyes of NCARB, could someone please explain the difference in these terms? I’d appreciate it!

0

• 

  manuelgranja October 11, 2024 21:14

  Vapor barriers and vapor retarders are treated similarly by NCARB, classified by permeability (Class I, II, III). Both control water vapor diffusion, with Class I (impermeable) fully blocking vapor and Classes II/III allowing controlled movement. Moisture barriers, also known as water barriers, block liquid water but are often vapor-permeable. Air barriers prevent wind-driven air infiltration but do not address vapor created by temperature differences between interior and exterior environments. Each serves specific functions: vapor barriers for vapor control, moisture barriers for water, and air barriers for wind, depending on climate and construction needs. For the exam is important that vapor barriers usually go on the hotter side of the insulation, Exterior side in Florida, interior side in Minnesota.

  3

  Comment actions Permalink
• 

  GiselleCastillo October 02, 2025 21:01

  Meany the warmer side of the assembly, after the wall sheathing is installed for Florida weather? In other worlds, framing, insulation, sheathing and then the vapor barrier and ultimately the stucco ? 

  1

  Comment actions Permalink
• 

  Ralph Hale October 03, 2025 13:52

  https://buildingscience.com/documents/digests/bsd-106-understanding-vapor-barriers
  
  This is the article I always share when folks have that question.  Manuel is spot on, with the exception that an air barrier is almost always also either a vapor retarder or a vapor barrier, all vapor barriers are air barriers, and water barriers may or may not be vapor or air control layers as well.  Each definition has a specific function, but one material may meet more than one definition.  
  
  Best,
  Ralph, the Amber Book Team

  0

  Comment actions Permalink

Please sign in to leave a comment.