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I am finishing a basement with my father and want to put in a subfloor. I know if there was ever enough water I would probably have to replace the floor anyways but want to give myself a couple inches more so to protect the expensive electronics I will have down there. There is also a sewer access port and two ground rods that stick ~ 2 inches above the concrete floor.

We were originally planning to lay down pressure treated 2x4's the tall way getting us over the two obstructions and build a plywood floor on top of it. After that we were going to build two small access panels in the floor should we ever need to get to them.

An uncle who is a carpenter stopped by this weekend and said if it was his basement he would not even bother building a subfloor. He said the basement was bone dry and it would be a waste. Even if we did get water it would be trapped in between the 2x4's with no way to get it out. The obstructions are in a corner so we would just box them in somehow going that direction.

This now puts me back to planning. I can't see a disadvantage to building a subfloor other than money and height though the ceiling down there is 8ft so height is not an issue.

What is the best way to build the basement subfloor? I have seen other methods such as Dri-Core or Delta-FL also suggested. Ideally I would like to create channels so I could somewhat push water out should I ever have an issue. From concrete to carpet please advise me exactly what I need to do in-between.

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3 Answers

I have tried several methods and the best one I have used it foam board on the bottom and 3/4 inch plywood over. I would never lay down wood on the floor. Not only will it rot but it will retain moisture.

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Does the foam allow water to travel or is it solid? If I were to use pressure treated sleepers wouldn't this help with rotting? –  user15608 Oct 14 '13 at 18:13
    
Foam board allows water to escape out. I would only think about solid foam or some sort of rubber (what dri-core uses) for the bottom of a basement subfloor. –  DMoore Oct 14 '13 at 18:15
    
I have seen Dri-Core. Is it just regular old foam board you use on top of the concrete? Nothing else? –  user15608 Oct 14 '13 at 18:34
    
homedepot.com/p/t/100320356#.UlxEJBDOSZc - you can glue them down but it is a waste of time because glue will eventually fail. Float them and tape the seems. Stagger the seems, then stagger the plywood seems. You can nail down the plywood but make sure that you use coated nail (tapcons) or something similar. –  DMoore Oct 14 '13 at 19:23
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Treated wood against concrete, and not constantly submerged isn't going to rot. If you have a stick framed house then you likely have treated wood against your footing. –  Matthew Oct 15 '13 at 15:45
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Putting wood on the concrete in the basement is typically called "sleepers."

You will, without a doubt, be retaining moisture in this layer beneath the finished floor so a proper barrier is paramount. Also, consider that your basement floor is (or should be!) sloped towards the drain so your sleepers will not be flat for your finished floor.

I have a few suggestions if you intend to proceed:

  • Use 4x4 instead of 2x4 to make fastening easier into the concrete base
  • Use a "forgiving" finish floor such as carpeting or tile (as you can level with thinset and/or layers of subflooring)
  • Sleepers should have a clear path for water to run toward the drain. Never create pockets or lay sleepers perpendicular to the flow of water. This may align sleepers in a "star" pattern out from the drain or maybe you should cut channels in the sleepers to permit water to run
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    4x4's are a great idea. What all do I need between them and the concrete? –  user15608 Oct 14 '13 at 17:59
        
    I would paint the concrete with a sealant and then I would probably double-layer a vapor barring above them, under the plywood. –  Matthew Oct 14 '13 at 18:00
        
    Any suggestions for a vapor barrier, links to products? –  user15608 Oct 14 '13 at 18:34
        
    @user15608 I have used Tyvek housewrap products but I don't know if they'd be appropriate for this use. Perhaps something like this? solutions.3m.com/wps/portal/3M/en_US/Adhesives/Tapes/Promotions/… –  Matthew Oct 14 '13 at 19:07
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    I suggest some reading at buildingscience.com. For example, this one might be helpful: http://www.buildingscience.com/documents/bareports/ba-0309-renovating-your-basment/view?topic=resources/more-topics/homeowner_resources

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    -1 Link only answers become useless when the link goes bad and are frequently confused with spam. Be sure to provide context around the link and quote relevant content in case the link goes bad. See how to answer for more details. –  BMitch Oct 29 '13 at 12:25
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