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Two sub-floor questions...


ruauu2's Avatar
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08-24-13, 10:16 AM   #1  
Two sub-floor questions...

I'm replacing the plywood sub-floor in my hallway before I have new carpet installed. Home was built in 1956.

The plywood is on top of a "first" sub-floor of diagonal 1 x 12s. There was tar paper ("felt"?) laid below the plywood and the old felt is being discarded.

There is an unfinished basement below.

1) Do I need to install some type of felt between the sub-floors?

2) Is leaving a small (1/16 to 1/8) gap between sub-floor panel edges sufficient or is some sort of spacing material recommended? (The original plywood had strips of felt to act as spacers.)

Thank you for your time!

 
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Furd's Avatar
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08-24-13, 12:01 PM   #2  
I am not a builder so what I suggest may not be the best method.
At my previous home I added a 6 mil polyethylene vapor retarder over the subfloor and then 1/2 inch exterior plywood before installing the finished flooring. Prior to this the floors were so cold that walking in your bare feet took the risk of your feet sticking (freezing) to the floor. (Only a slight exaggeration). After installing the poly the floors were comfortable to bare feet.

 
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08-24-13, 01:08 PM   #3  
Why are you replacing the plywood?
Add some screws to the old 1X's before installing the plywood.
The underlayment needs to be subfloor rated and attached every 4" on the edges and 6 to 8" in the field.
A tiny gap will be fine so there's no wood on wood contact to cause squeaks.
A layer of tar paper may also help stop any squeaks.

 
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08-24-13, 01:24 PM   #4  
Why are you replacing the plywood?
Pet stains (urine)

The underlayment needs to be subfloor rated
I wanted to buy it at Lowe's and the only choices in the thickness I need are OSB sheathing and pine sheathing.

Will either of those be okay?

Thank you for your time and help!

 
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08-24-13, 01:49 PM   #5  
Put in a floor rated 3/4" OSB T&G Like Advantech (box stores have their own name). This will give you the best performing floor for the money. Screw the new layer down with at least 2" exterior rated screws per previously mentioned nailing method. 15# felt paper (in roofing dept) is the least expensive vapor barrier and replaces what you already had there.

Dog obedience training is what is going to bust the budget.

 
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08-25-13, 11:41 AM   #6  
Thank you, czizzi.

I cannot use 3/4" without going to a lot of extra work - that's why I wondered if the product referred to as "sheathing" would be okay?

Also, since there is a sub-sub-floor, the T&G would not be as necessary?

 
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08-25-13, 01:11 PM   #7  
The boards are your subfloor, plywood the underlayment- slip sheet (other than poly sheeting is fine) between the two; UMass Amherst: Building and Construction Technology Wood Underlayments for Resilient Flooring

Here is the plywood guide for your underlayment- end gaps, fasteners (not into joists), grades, etc.; http://www.google.com/url?sa=t&rct=j...KEftFQ&cad=rja

Never use poly sheeting to trap moisture in the plywood; if high RH the ply will hold the moisture wetting carpet backing for mold or; any vinyl on top with plastic under ply will be a vapor barrier sandwich. Laminate Flooring Underlayment

"Moisture"; Installation - A Guide to Subfloors Used Under Wood Flooring

Gary

 
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08-25-13, 01:19 PM   #8  
The pet stains and smell can be treated with an enzyme cleaner and sealed with a stain blocking primer instead of all the work of replacing the underlayment.
Both Lowes and Home Depot carry underlayment rated 3/8, 1/2 and even 1/4 underlayment.
Regular sheathing is full of voids in the core and unfiled knots on the outside and should not be used.

 
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