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Discussion Starter #1
Hi,

I've been DIY-ing a small room in my basement (approx. 10'x16').

I'm now onto flooring and looking for some advice. I'm planning to lay carpet and the existing floor is a regular concrete slab. We've never had any water issues in the basement and I've done the moisture test with plastic sheets and found nothing.

I know I'll need some type of subfloor, but I'm getting concerned about height. I'm currently at 80" from the concrete to the drywalled ceiling. So what's my best option in terms of reduced thickness but protection from any potential moisture?

Can I get away with just 1/2" foamboard with the underpad and carpet directly on top of that?

And does foamboard need to be drilled into the concrete? Or would an adhesive be sufficient?

Thank you!

- H
 

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What I have done is laid 6 mil. plastic on the slab, a layer of 3/4" foam (1/2" would also be fine) then Advantech T & G subflooring Tap Coned down with 3" X 1/4 flat head screws, no glue anywhere.
It was done about 10 years and it worked out fine for me, it's never moved.
I had laid Allure flooring over it, which was a big mistake, Just last week I removed it and replaced it with 100% waterproof vinyl plank flooring and saw no moisture damage to the Advantech at all.
The foam acts as a thermal brake and the floor feels warmer.
 

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Discussion Starter #5
They make tack strip with concrete nails for a reason. I have had carpet in about ten basements with out any issue.
So you're laying the carpet directly on the slab? Never had any moisture issues? That would make me nervous - everything I've read says it's best to have some kind of barrier in case of moisture...

Can I get away with 1/2" foamboard with the underpad and carpet directly on top of that? And just letting the foamboard float?
 

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So you're laying the carpet directly on the slab? Never had any moisture issues? That would make me nervous - everything I've read says it's best to have some kind of barrier in case of moisture...

Can I get away with 1/2" foamboard with the underpad and carpet directly on top of that? And just letting the foamboard float?
Moisture is an issue that should be solved long before you do any finish work. Foam board would need a fire stop on top I think. On wall it needs to be covered with drywall so the floor would likely need plywood or something. We just put down the foam underlay for carpet.
After tile carpet is the easiest to clean up after a flood.
If you put down a vapour barrier and you do have water, where do you suppose it will go as it builds up under there?

Tape pieces of plastic sheeting to the floor and see if you have moisture on top, that would be condensation from above. water under it would be a problem from below that would need to be solved before going forward.
 

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Discussion Starter #7
Mentioned in my original post that I'd done the moisture test with plastic sheeting - no issues at all.

What type of underlay do you use? Is there a certain type that best for applying directly on concrete?
 

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I put down regular foam carpet pad and then carpet. Never had an issue. As has been said, know the basement is dry before hand.
 

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retired framer
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Mentioned in my original post that I'd done the moisture test with plastic sheeting - no issues at all.

What type of underlay do you use? Is there a certain type that best for applying directly on concrete?
I have always used the underlay that best matches the carpet being used as suggested by some salesman, never gave it much thought and never had a problem. Right now I am re arranging some walls in a friends basement suite and re using what was there. Two different colours of underlay but both seam to be similar 1/2" thick bits of foam glued together with a film of some sort on top. It has been there with out a problem for about 15 years.
 
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