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Old 04-17-2012, 08:18 PM   #1
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Adding a floor over a floor with insulation in between.


Hi

There is already a floor. I want to add 2x 4's on top of existing floor, insert insulation between 2 x 4's, then install new floor on top of 2 x 4's.

Will this create a moisture problem between the floor layers where the insulation is? If so, is there a way to prevent that from happening?

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Old 04-18-2012, 12:47 AM   #2
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Adding a floor over a floor with insulation in between.


Depeds on what's below the floor you have now.
Is this in a basement?
Is there a crawl space of basement under it?
Adding a sleeper floor will through off all your door and baseboard heights.

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Old 04-18-2012, 01:56 AM   #3
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Adding a floor over a floor with insulation in between.


There is a small space under the existing floor but underneath is the ground. Floor gets very cold during the winter. I figured I would have to cut a few inches off the bottom of the door if adding insulation and another layer of flooring without a condensation problem is possible.

Originally was going to pull up existing floor, add insulation then refloor but this would be easier and I thought the extra layer of floor would keep everything warmer.
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Old 04-18-2012, 02:46 AM   #4
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Adding a floor over a floor with insulation in between.


How small? Can you get underneath?
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Old 04-18-2012, 09:34 AM   #5
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Adding a floor over a floor with insulation in between.


There is no way to access under the floor without ripping the floor up. I apologize for not including more details in the original post. I can do odd and end carpentry and fix it repairs but sometimes do not think of everything involved or needed until afterwards sometimes due to lack of experience. Attempting to avoid errors this time with help from individuals that know more than I do.
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Old 04-18-2012, 09:55 AM   #6
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Adding a floor over a floor with insulation in between.


If its concrete underneath, and you think there is a chance of moisture seeping thru, you are better off going with a moisture barrier before the 2x4s. Better still to use pressure treated 2x4s.
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Old 04-18-2012, 10:07 AM   #7
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Adding a floor over a floor with insulation in between.


No concrete underneath. A previous owner added this back room. From what I can see, looks like they put beams supported by a concete outer rim with masonary blocks in between for the beams to rest on that are sitting on the ground. If you mean putting plastic sheeting on top of the exisiting floor will the moisture build up under the plastic and rot out the existing floor wood?
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Old 04-18-2012, 10:35 AM   #8
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Adding a floor over a floor with insulation in between.


If this was my job to do I would be removing the sub floor you have now,
while it's open take a look for termites and powder post bettles and fungus on the floor joist, air seal then insulated with foam panels, use Advantec subflooring installed with constrution adhesive on the joist.

Moden building codes call for any wood closer then 18" from grade must be pressure treated so all those floor joist are to close to the ground and are subject to all kinds of moisture caused problums, so a little PM will pay off.
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Old 04-18-2012, 10:37 AM   #9
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Adding a floor over a floor with insulation in between.


plastic sheathing has to done over concrete before wood, it will trap moisture.
For your case, if it has already a wooden floor, you need not worry much about moisture issues.
What type of insulation are you thinking of putting down?
Have you considered subfloor panels?
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Old 04-18-2012, 04:45 PM   #10
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Adding a floor over a floor with insulation in between.


joecaption,
I agree that checking what is going on under the existing floor would be better. There could be rotten wood underneath. Initially I was hoping to not have to rip out the floor and at the same time keeping the initial floor would help keep the room insulated better since so much cold comes up from the floor.
Air seal?
Insulate with foam panels instead of regular insulation? How are the foam panels attached between the joists?
Is this the flooring material you are talking about: AdvanTech 23/32 x 4 x 8 OSB Subfloor and can floor tile be put directly on that or does a layer of luan have to go over the Advantech?

BNTHERE,
With so much cold coming up through the existing floor then having a floor on studs above that with hot air above the new floor how could there not be condensation in between?
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Old 04-19-2012, 12:11 AM   #11
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Adding a floor over a floor with insulation in between.


I'd use 1/2" hardibacker board. Tape joints with mesh tape and thinset. Go over the whole floor with redguard (moisture barrier). Then thinset your plywood to the hardibacker.
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Old 04-19-2012, 10:33 PM   #12
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Adding a floor over a floor with insulation in between.


Are the joists 18" from the plastic covered dirt? 12" to the beams.

Gary
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Old 04-19-2012, 10:51 PM   #13
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Adding a floor over a floor with insulation in between.


Been doing some more research. Definitely going to have to pull the floor, clean out underneath, use plastic sheeting on the ground and side areas as a moisture barrier. Not much room to work under the floor so everything is going to have to be done from the top. Have to check distances. Only have a small spot cut out currently to look under floor. Will open gap a bit more and return with more info.

What a mess. There are bricks, pieces of wood, pieces of piping, junk and completely deteriorated fiberglass insulation laying on the ground under the floor.
Joists are approx 18" CTC.

Wow am I excited about this fun project!


Last edited by ThoughtIKnew; 04-19-2012 at 11:07 PM.
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