I have a 1950’s ranch house in Denver, CO., slab on grade. I wish to install hardwood flooring over this. I plan on installing treated 3/4″ sleepers, shot and glued to the slab, (I’m using this space to run electrical, water lines, etc.), then 3/4″ sub-floor and then the 3/4″ hardwood. Here’s the question: do I need to install any sort of vapor barrier within this assembly? My contractor says no, a vapor barrier will trap any moisture, creating a problem, besides you can’t glue the to the barrier. He thinks that allowing the floor to “breath” will be a better approach. Several hardwood installers, but not all, recommend a barrier everywhere from directly on top of the slab to between the sub-floor and hardwood. I’m baffled, what is the best approach here?
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Your proposed installer/comntractor doesn't know his beans from his peas
Ground moisture will wick up through the slab and make the backside of the hardwood swell more than the topside, creating cupping.
The only way he should be making such a statement is if he can gaurantee that there is no groundfwater and that there will nerver be any.
In new construction there are ways to control this like placing a sound VB under the 'crete when pouring, and then sealing the 'crete. Even then, I would backprime the flooring before installing it.
His concern is trapping moisture... OK, Let's go with that. Trap it where it will do the least harm. Use PT sleepers, and then place the VB over the sleepers and screw the subfloor down to them.
A way to test moisture migrating thru the slab from the ground is to tape down a 2' square of plastic over the slab for a few days to see if moisture collects under it. But a negative result could be a false negative because your ground water levels may fluctuate from one season to the next.
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Thanks for your help. Sounds like good advise.
If i were to take his approach, I would place the sleepers at 12" OC, dispense with the plywood and seal the back sides of the flooring with shellac, two coats.
But that is going to be a compromise
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