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I will be framing out my basement with steel so the bottom track will be on the concrete slab.

Is it required to put some sort of vapor barrier between the slab and the track? I couldn't find anything in the code that indicated it was required but want to make sure I pass inspection.

If it isn't required by code, is it recommended? My gut says it's unnecessary since the metal is galvanized, but I've seen arguments for and against it.

If some sort of barrier is required or recommended, what would you use and how would you install that?

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    Just checked my local big box website. 82 feet of foam sill plate vapor barrier costs 8 bucks. At that price, and amount of effort required, Why wouldn't you? Oct 23, 2020 at 16:25

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Vapor barrier is required by practical considerations, not by code (at least in the US).

For concrete slab placed over soil with high water content, it is good idea/practice to provide the vapor barrier, to prevent the floor from getting moist/wet, and make the living space too damp. Galvanized steel itself is water/moisture resistant, but, in a enclosed, humid, not well ventilated environment, the connections, connected parts, and the hidden contact surfaces can collect/accumulate water from the moist air, that may leads to adverse effects, and causing damages.

There are many different types of vapor barriers, each has its own advantages and disadvantages. The barrier should be placed over a layer of sand, which is placed on top of the compacted gravelly backfill. For barrier selection, you shall consult with an engineer, or your contractor, if he/she is quite familiar with the practice in the local area.

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I'm not aware of any requirement or recommendation to use a vapor barrier between a concrete floor and wooden framing, so I can't see why there would be one for metal framing.

Pressure treated lumber could be used for the sill plate if you were doing it in wood, so I'd think that would have a similar water damage resistance to galvanized steel studs.

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  • A moisture barrier is required for wood framing if the bottom plate is not treated against rot. There must be isolation. That's maybe what you intended to convey in your first paragraph, but it's not clear.
    – isherwood
    Dec 8, 2023 at 21:32

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