Where is a 6-mil polyethylene (Visqueen) vapor retarder not required under a concrete floor slab on grade?
Wednesday, April 24, 2019
The required 6-mil polyethylene (or other approved) vapor retarder sheet under a concrete floor slab is necessary for the living spaces in a home because it keeps moisture from rising through the slab in wet weather and saturated soil. But the International Residential Code (IRC) and the Residential Edition of the Florida Building Code (FBC 506.2.3) do not require it in the following areas, which are essentially all unheated areas that are not likely to be enclosed for living space in the future.
The exception number 1 refers to garages that are “accessory buildings,” which means that garages that share a common wall with the home are not exempt from the vapor retarder requiremCarports and patio floor slabs that were installed without a vapor retarder barrier tend to sweat and become slippery occasionally when they are enclosed later into living space. To read more about it, see our blog post Why does my concrete floor slab sweat and get slippery?
Also, see our blog post Why are there score line grooves in the concrete floor of the garage?
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