Do I Need A Subfloor If I Put Rigid Foam Under Slab? - Building & Construction - DIY Chatroom Home Improvement Forum

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Old 02-17-2016, 03:22 PM   #1
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Do I need a subfloor if I put rigid foam under slab?

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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Old 02-17-2016, 03:52 PM   #2
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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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Old 02-17-2016, 07:33 PM   #3
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Risky business in a new house laying hardwood down. Like stated above you have know idea what will happen through the seasons. I just went to a house where they layed Brazilian cherry in the basement of a new home. It got wet over a rainy weekend and the floor buckled about a foot off the ground.
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Old 02-17-2016, 08:00 PM   #4
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basement gamble

as stated earlier in this thread without a history you really have no idea what is going to happen. It sounds like what the builder is offering is great in regards to keeping temperature changes to a minimum, but I do not believe that there is any type of moisture benefit with the product you mentioned.
What are the soil conditions in the area?

Does everyone in your area have basements? Do they have issues with water finding its way in?

Has the builder done what they should of in regards to making the outside of the basement water tight? And are there drainage pipes all the way around the foundation to help bring any type of water that is trying to get in away from the basement?

All items to take into account.

safe wau to test it out is to install something that will not break the bank it it does fail

Example..... textured vinyl has teh same appearance as engineered hardwoods when installed properly

Good luck
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