GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Vapour Barriers

marcus1977 | Posted in General Questions on

Hello is it more likely that more water vapour is carried through a wall assembly by air leakage than vapour Diffusion? Can the perm rating of a paint change over years if there is a roof leak causing moisture issues with in a home?
zone 5 in the country.
Thank You for your time.

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. Expert Member


    Yes, exponentially more moisture makes its way into most building assemblies through air leakage than does through diffusion.

    I'm sorry I don't know how roof leakage affects the permeability of paints.

    1. marcus1977 | | #3

      Thank you so much for your input

  2. Expert Member
    BILL WICHERS | | #2

    I'm not aware of any information as to paint chaning it's properties over time. I would expect the vapor control properties of paint to remain relatively stable over time though, unless you have peeling, cracking, or other issues showing failure of the paint.

    I don't see how a roof leak applies here. If a roof leak is letting moisture into the home in the form of bulk water (drip drip, trickle, etc.), then the air sealing and moisture control of the building isn't really the problem, the leaky roof is.


  3. marcus1977 | | #4

    Thank You so much for your reply

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |