Vapor barrier behind drywall (Zone 4a) - GreenBuildingAdvisor
Summary
The article discusses the implications of having a plastic vapor barrier behind drywall in a Virginia porch, focusing on potential mold growth and insulation concerns.
Why It Matters
Understanding the role of vapor barriers in construction is crucial for maintaining healthy indoor environments, especially in regions like Zone 4a where humidity can lead to mold issues. This discussion highlights best practices for insulation and moisture control.
Key Takeaways
- Plastic vapor barriers in conditioned spaces can promote mold growth.
- Removing problematic barriers is essential for maintaining indoor air quality.
- Consider replacing fiberglass insulation with mineral wool for better moisture management.
Vapor barrier behind drywall (Zone 4a) thomas_mitchell | Posted in General Questions on February 22, 2026 03:53pm Hi all,I have a small finished porch that I am redoing. The porch currently has heat but is not air conditioned – I plan to add air conditioning. The porch was closed in over 10 years ago, but not sure exactly when. I know there are a few spots with water entry and bug damage. I opened up the walls and found a plastic vapor barrier on the other side of the drywall, followed by paper/foil backed fiberglass insulation and then some kind of foam insulation on the other side of the studs (not sure how thick this is). I’ve never seen a plastic vapor barrier like this before (I’m in Virginia) and from a basic search, it seems like this will induce mold in a conditioned space. That said, I wanted to ask if I’m missing something here. More than anything the goal is to create a space that is not conducive to mold growth. Would prefer not to fully re-insulate and drywall – but I will if the current setup is asking for trouble. Thanks! Answer GBA Detail Library A collection of one thousand construction details organized by climate and house part Search and download construction details 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. Start free trial Related Questions Smart membrane behind drywall – pointless? Void space behind d...
