How to Choose the Right Vapor Retarder for Your Climate Zone
By Graham Mann | Published: 12/14/2025
Which vapor retarder class (I, II, III) fits your U.S. climate zone? Learn placement, material choices, and installation tips to prevent condensation, mold, and energy loss.
How to Choose the Right Vapor Retarder for Your Climate Zone Moisture can damage your home's structure, promote mold growth, and reduce insulation efficiency. Vapor retarders help control water vapor movement, but choosing the right one depends on your climate zone. Here's what you need to know: - What are Vapor Retarders? Materials that slow vapor movement, categorized into three classes by permeability: - Class I: Low permeability (e.g., polyethylene, aluminum foil) for cold climates. - Class II: Moderate permeability (e.g., kraft-faced insulation) for mixed climates. - Class III: High permeability (e.g., latex paint) for hot, humid areas. - Climate Zones in the U.S.: - Zones 1–2 (hot, humid): Avoid interior vapor retarders; use Class III if needed. - Zones 3–4 (mixed): Use Class II or III; avoid Class I on interiors. - Zones 5–8 (cold): Use Class I or II on interior walls to prevent condensation. - Installation Tips: Place vapor retarders on the warm side of walls. Seal gaps and pai...
← Back to all articles