best location for vapor barrier under slab - GreenBuildingAdvisor
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I’m looking at these 2 details from the library. The monolithic slab shows a vapor barrier above the insulation, wrapping around the footing. The second image with the non-structural slab […]
best location for vapor barrier under slab Antonio Bettencourt | Posted in Energy Efficiency and Durability on March 4, 2026 11:57am I’m looking at these 2 details from the library. The monolithic slab shows a vapor barrier above the insulation, wrapping around the footing. The second image with the non-structural slab shows no vapor barrier at all. Where would be the best place to put one? Or is none necessary? Normally it seems best to put the vapor barrier ABOVE the insulation for constructibility reasons. Do that here and let it wrap up to the top of the edge insulation? 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 Foam + vapor barrier under slab? Vapor barrier under slab, constructibility question Vapor barrier under slab???? Insulated basement slab vapor barrier location - above or below the under-slab insulation? Replies Expert Member MALCOLM TAYLOR | Mar 04, 2026 12:33pm | #1 Antonio, You definitely want a poly vapour-barrier, and it's best located directly under the slab. https://www.greenbuildingadvisor.com/article/polyethylene-under-concrete-slabs JerrySmith | Mar 04, 2026 12:43pm | #2 I noticed the mention of placing a vapor barrier un...
