# Sleeper Floor Over Concrete - Vapor Barrier?



## ianpfeiffer (Jun 7, 2020)

Howdy,
Got a question on where/whether to put a vapor barrier in a sleeper floor on concrete.

I've got a customer who's expanding their living space into the garage and we're framing a new floor on the slab. Only problem is, the floor we're matching to is 3" above slab surface so we need to make it a sleeper floor.

The customer wants to make sure they never get a musty smell because they're planning on installing carpet in the room over the slab. So moisture control is important here.

The slab is ~4" above grade and has a 6mil vapor barrier but it isn't insulated.

It seems like best practice here would be to install PT 2x4 like the link here for the sleepers:
https://www.proremodeler.com/raising-1960s-sunken-living-room-floor

BUT should I put 6mil vapor barrier over the slab, then ramset the PT 2x4's or just put down the PT and put the vapor barrier under the subfloor? OR just no vapor barrier?

Can't seem to find consistent info here. Anything helps, Thanks!


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## META (Apr 9, 2015)

I don't like the idea of trapping moisture with wood. I'd put the VB directly on the cement. Any moisture that does condensate on the upper side of the VB then at least has the ability to evaporate in the small air space.

Sent from my SM-N950U using Tapatalk


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## wallmaxx (Jun 18, 2007)

seal it with some kind of acrylic or industrial coating. Line-x even does concrete floors.


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## ScipioAfricanus (Sep 13, 2008)

ianpfeiffer said:


> Howdy,
> Got a question on where/whether to put a vapor barrier in a sleeper floor on concrete.
> 
> I've got a customer who's expanding their living space into the garage and we're framing a new floor on the slab. Only problem is, the floor we're matching to is 3" above slab surface so we need to make it a sleeper floor.
> ...


If you are saying that there already is a 6 mil. VB under the garage slab then I would say that you don't need anything else.

Andy


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## hdavis (Feb 14, 2012)

My advice could depend in where you live and the HVAC. Here, you can get condensation just from the slab temp being below the dew point at times, usually early summer here.

Usually not a problem.


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## Seven-Delta-FortyOne (Mar 5, 2011)

First thing you need to do is tape a piece of clear poly over the slab, and check it for moisture after 24 hours. :thumbsup:


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## greg24k (May 19, 2007)

If you want additional protection use the XPS foam board, but if there is plastic already and you 4" above the grade you don't need anything.


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