Carpet on Basement floor - 6mm poly first?

I am about to install a 12*12 carpet into an office I have newly renovated in the basement. My intentions were to put the underpad against the bare concrete floor and then then carpet on top. I have heard from some that I should first put down a layer of the 6mm vapour barrier and then put the underpad and carpeting? Comments?

 

Good evening. I would suggest you put several 3'x3' pieces of poly on the floor in different locations and duct tape the edges of each piece. Leave it there for several days and see if you get any moisture showing up on the underside of the poly. If it stays dry you can lay the carpet directly on the cement. Since there is no way to attach a separate underpad to the concrete; I suggest you look into commercial grade carpeting with latex or foam attached to the carpet. This is what I used in my rec room. The first carpet lasted through three kids and 25 years. The replacement carpet is the same construction but the installers totally glued it to the floor which stops the problem of carpet stretching or creeping. If you do have moisture under the poly after the test; there are special plastic panels that can be glued or screwed to the floor under the carpet for moisture barrier. Sheet poly will slip and slide and your carpet will follow it.
Hope this helps and please let us know how the job is going.
Have a good day.