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Do I need a subfloor if I put rigid foam under slab?

792 Views 3 Replies 4 Participants Last post by  proudveteran
Hi Everybody,

I'm building a new home and the builder has an upgrade to add R10 rigid foam board under the slab. I'm planning to finish my basement. I'm still thinking about flooring options... do I need any kind of subfloor or vapor barrier... I would think not as it would create a pocket between the subfloor and rigid foam under the slab??

I might end up using engineered hardwood that can be floated on concrete slab...

Any ideas on whether I would need a sub-floor? Thanks in advance.

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Hi Jack,
I've added a link below to explain what I don't have space here to do. But achieving a dry basement is a lot more than just adding rigid under the slab. Building new you have the problem of no history. An existing home in a dry climate with dry soils might qualify for finishing the basement with a high level of confidence, but moist soils in an average climate it becomes risky. Sure, many do it, but some fail dramatically.

I'll let you read and you can follow their other links for a ton more articles, this is a common topic. But a dry basement is a complicated process and most of the effort goed into the ground before the house is built.

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