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Old 12-21-2011, 11:52 AM   #1
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Replacing underlayment in entire house...what material to use?


Hi All,

I am getting ready to replace all of the underlayment in a house that I am remodeling and would like to get other opinions on what material to use.

The house was built in the late 60’s. It is about 1600 sq. ft., has 4 bedrooms and 2 full baths. There is a 15’ x 15’ atrium in the center of the house which is open to the outside. There are 4 (6’ x 3’) windows per side. So a total of 16 windows around the center of the house. The floor joists are 2 x 10’s. I am not sure about the wood but it sure looks like cedar to me.

The original sub-floor is ½” plywood on top of which was installed a layer of 5/8” particle board as the underlayment. I have removed all of the particle board. A lot of it around the center of the house had been damaged (along with some of the ply sub-floor) over the years because the windows hadn’t been properly sealed.

I plan on putting tile in both bathrooms, a small kitchen and adjoining foyer. I will probably go with carpet in the rest of the house but laminate is still an option. Let’s just assume carpet for now.

I have some concerns with the transitions from tile to carpet which is one reason I am getting so caught up on the thickness of underlayment to use. I am getting ready to install tile in the master bath which is layered as follows: ½” ply sub-floor + ¾” ply underlayment + unmodified thinset + ¼” hardiebacker + modified thinset + approx. 0.3” tile = approx. 2”. I am using ¼ x 3/8 x ¼ notched trowel between hardiebacker and tile and ¼ x ¼ x 1/4 notched trowel under the hardiebacker. I plan on using the same layering of materials for the other bath, kitchen and foyer.

I plan on shimming the carpet at any threshold where it meets tile and want the carpet to butt to the tile with no transition piece. Will I have an issue with the height build up of the ply + thinset + hardiebacker + thinset + tile?


Right now I have 4 options in mind for the underlayment:
1) 5/8” ply
2) ¾” ply
3) 5/8” OSB
4) ¾” OSB

Here are some Pros and Cons of each:

5/8” Ply
Pros:
1) Will match original underlayment height so there should be less under cutting of door jams.
2) A bit easier to work.
3) Less weight on the floor joist. Not sure is this is even an issue.

Cons:
1) There will be a bigger height difference in the rooms which transition from tile to carpet (as opposed to using ¾” material) which I will have to make up somehow.

¾” Ply
Pros:
1) Makes for a stiffer floor.
2) I gain an extra 1/8” in height (as opposed to using 5/8” material) for areas which transition to tile.

Cons:
1) More weight on floor joists. Not sure if this is even an issue.
2) Will probably have to undercut door jams due to the added height.
3) A bit more difficult to maneuver around while installing.


OSB (5/8 or ¾)
Pros:
1) About ½ the cost of ply

Cons:
1) I have seen this debated before but since I have never used OSB I am a bit skeptical of the durability of this product.


I figured that I would need about 50 sheets of 4x8 material to complete the whole house. I will be shopping at Lowes since this is the most convenient place at the most reasonable price. The price difference between their Plytanium 23/32 x 4 x 8 Sturd-I-Floor T&G Plywood and Plytanium 19/32 x 4 x 8 Sturd-I-Floor Square Edge Plywood is about $1 so that’s not an issue. I would prefer a square edge 23/32 x 4 x 8 underlayment but Lowes doesn’t seem to carry that product.

OSB is about ½ the cost so the cost savings in about 50 sheets is around $500 so not a deal breaker either way for me. I would rather use plywood if it is the better product to use.

I am thinking that the 5/8” ply will be easier to install but for $1 more per sheet it seems crazy not to get a stronger product.

I know it would be better to have the thicker material on the bottom but since the ½” ply is under the walls I am kind of stuck with going with something similar to the original underlayment.

I would be really curious to hear what others would do in this situation. Have I left out any options? I plan on buying the material in quantities enough for a room or two at a time. Once I start purchasing and laying down the material, there will be no turning back.

Any feedback would be greatly appreciated!

-David


Last edited by Dave321; 12-22-2011 at 02:11 AM. Reason: changed formatting
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Old 12-21-2011, 02:01 PM   #2
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Replacing underlayment in entire house...what material to use?


You don't want square edge, you want tongue and groove subfloor material. Plywood or OSB doesn't matter, plywood is considered better by a lot of people. T&G may even be required by code.

I didn't read all of your post (way too long and confusing) so maybe you already know all of this. After that, there are several ways to deal with the tile installation and getting it to (basically) meet up with other floor coverings.

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Old 12-21-2011, 02:36 PM   #3
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Replacing underlayment in entire house...what material to use?


If I was given this job I would have also removed the 1/2, 1/2" is not a propper sub floor for any kind of flooring, all it's going to do is add height and act like a shim on the floor joist instead of a sub floor.
To remove it you will need a toe Kick saw and an ossilatiing saw. These can cut right up next to the walls without hurting them.
Then you can install 3/4" T & G Advantec sub flooring (stronger and more stable then plywood) with constrution adhesive on the floor joist. I like to use a stand up screw gun with 2 1/2" deck screws when attaching my subfloors, but ring shank 8D will work.
For a subfloor use 1/2 A/C plywood making sure the seams do not line up with the subfloor below.
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Old 12-21-2011, 04:39 PM   #4
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Replacing underlayment in entire house...what material to use?


Quote:
Originally Posted by joecaption View Post
If I was given this job I would have also removed the 1/2, 1/2" is not a propper sub floor for any kind of flooring, all it's going to do is add height and act like a shim on the floor joist instead of a sub floor.
1/2" sub-flooring is quote common when an additional layer is being added. It is extremely common where hardwood flooring is to be installed as the 1/2" is more for the contractor during the rough construction phase than for anything else. Removing it now would be a huge undertaking definately not worth your time or $.

5/8" of either OSB or ply will give you plenty of rigidity. You could get away with another layer of 1/2", but I would recommend 5/8" minimum. You can interchange thicknesses from room to room depending on your final finishes to ensure flush transitions throughout.
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Old 12-21-2011, 04:41 PM   #5
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Replacing underlayment in entire house...what material to use?


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Originally Posted by joecaption View Post
Then you can install 3/4" T & G Advantec sub flooring (stronger and more stable then plywood) with constrution adhesive on the floor joist. I like to use a stand up screw gun with 2 1/2" deck screws when attaching my subfloors, but ring shank 8D will work.
For a subfloor use 1/2 A/C plywood making sure the seams do not line up with the subfloor below.
So, you want him to remove the 1/2" plywood only to reinstall it? How is that different from just adding the 3/4" ontop of the 1/2"? Either way you slice it, it's still 5/4" of plywood...
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Old 12-21-2011, 09:35 PM   #6
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Replacing underlayment in entire house...what material to use?


sounds like a great home. Send a floor plan.

I don't think you mentioned what the span is on the 2x10's.

So please post a floor plan with dimensions!
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Old 12-22-2011, 02:23 AM   #7
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Replacing underlayment in entire house...what material to use?


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Old 12-22-2011, 02:33 AM   #8
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Replacing underlayment in entire house...what material to use?


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Originally Posted by Bud Cline View Post
You don't want square edge, you want tongue and groove subfloor material. Plywood or OSB doesn't matter, plywood is considered better by a lot of people. T&G may even be required by code.

I didn't read all of your post (way too long and confusing) so maybe you already know all of this. After that, there are several ways to deal with the tile installation and getting it to (basically) meet up with other floor coverings.
Sorry for the wordy post. I was try to make sure that I didn't leave out any details. Would I sill need tongue and grove since there is already the 1/2" ply? I don't have any problem using tongue and grove it just might limit my options given the limited availability of suppliers near by. By the way, the existing 1/2" ply is pretty sturdy as is. I wish they still made it like that today.
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Old 12-22-2011, 03:02 AM   #9
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Replacing underlayment in entire house...what material to use?


Ag reread my post, It suggest removing the 1/2 and replacing it with T&G 3/4 Advantec then a layer of 1/2 over that.
And no it's not common to see 1/2 subflooring even on a shed, yes I have seen it before but when I did see it, it was being replaced becuse someone was installing tile. and the old subfloor looked like a bumpy back road with low spots betwen the floor joist.
Show me proof where 1/2" plywood is an exseptable sub floor for tile.
Really old houses 9around 100 years old) some times used true 3/4 X 6 pine sitting diaganal, some even used 3/4 hard wood directly nailed to the floor joist. But never 1/2 anything.
The only time I've seen 1/2 plywood used was a DIY built home or lower end homes built in the 70's as a cost cutting effert.
No building inspecter would ever allow 1/2" to be used today as the main subfloor.
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Old 12-22-2011, 03:20 AM   #10
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Replacing underlayment in entire house...what material to use?


Quote:
Originally Posted by joecaption View Post
If I was given this job I would have also removed the 1/2, 1/2" is not a propper sub floor for any kind of flooring, all it's going to do is add height and act like a shim on the floor joist instead of a sub floor.
To remove it you will need a toe Kick saw and an ossilatiing saw. These can cut right up next to the walls without hurting them.
Then you can install 3/4" T & G Advantec sub flooring (stronger and more stable then plywood) with constrution adhesive on the floor joist. I like to use a stand up screw gun with 2 1/2" deck screws when attaching my subfloors, but ring shank 8D will work.
For a subfloor use 1/2 A/C plywood making sure the seams do not line up with the subfloor below.
Thanks for the suggestion. Sounds like a nice ideal to have the sub-floor which is in direct contact with the floor joists be 3/4" but this would be a very labor intensive effort. This would require blocking any place the sub-floor runs parallel with the floor joists and potentially under interior walls. I assume the 1/2 A/C plywood would be used as the underlayment on top of the 3/4" sub-floor?

I would think that the original 1/2" sub-floor is only going to add to any additional material installed on top of it. It is "old school" 1/2" ply and is fairly strong as is.
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Old 12-22-2011, 03:38 AM   #11
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Replacing underlayment in entire house...what material to use?


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Originally Posted by joecaption View Post
Ag reread my post, It suggest removing the 1/2 and replacing it with T&G 3/4 Advantec then a layer of 1/2 over that.
And no it's not common to see 1/2 subflooring even on a shed, yes I have seen it before but when I did see it, it was being replaced becuse someone was installing tile. and the old subfloor looked like a bumpy back road with low spots betwen the floor joist.
Show me proof where 1/2" plywood is an exseptable sub floor for tile.
Really old houses 9around 100 years old) some times used true 3/4 X 6 pine sitting diaganal, some even used 3/4 hard wood directly nailed to the floor joist. But never 1/2 anything.
The only time I've seen 1/2 plywood used was a DIY built home or lower end homes built in the 70's as a cost cutting effert.
No building inspecter would ever allow 1/2" to be used today as the main subfloor.
I think for awhile around the 60's and early 70's the method of using 1/2" ply as the sub-floor with 5/8" partical board on top as the underlayment was used by some builders. Probably a cost thing. Maybe a region thing. At some point they must have figured that partical board wasn't such a good thing. Especially when it gets wet! Partical board provided a decent surface for linoleum which was used alot back then as well.
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Old 12-22-2011, 04:25 AM   #12
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Replacing underlayment in entire house...what material to use?


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sounds like a great home. Send a floor plan.

I don't think you mentioned what the span is on the 2x10's.

So please post a floor plan with dimensions!
I don't have a detailed drawing. I have a rough sketch from my termite inspection that I will try and post (probably not too helpful). Floor joists run from outside of house to atrium wall on all four sides. The house is on a crawl space. I can check on the joist span this weekend and any other measurements.
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Old 12-22-2011, 07:17 AM   #13
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Replacing underlayment in entire house...what material to use?


Quote:
Originally Posted by joecaption View Post
Ag reread my post, It suggest removing the 1/2 and replacing it with T&G 3/4 Advantec then a layer of 1/2 over that.
And no it's not common to see 1/2 subflooring even on a shed, yes I have seen it before but when I did see it, it was being replaced becuse someone was installing tile. and the old subfloor looked like a bumpy back road with low spots betwen the floor joist.
Show me proof where 1/2" plywood is an exseptable sub floor for tile.
Really old houses 9around 100 years old) some times used true 3/4 X 6 pine sitting diaganal, some even used 3/4 hard wood directly nailed to the floor joist. But never 1/2 anything.
The only time I've seen 1/2 plywood used was a DIY built home or lower end homes built in the 70's as a cost cutting effert.
No building inspecter would ever allow 1/2" to be used today as the main subfloor.
1) I did read yours, but have you? 5/4" thickness of plywood is a 5/4" thickness of plywood. Whether the 3/4" is on the top or bottom has no real relevance to the overall performance of the system. Unless, of course, you don't screw it together...but why would anyone do that?
2) I never said it is used as a basis for tile. I simply said it was used as a rough construction floor system. Where tiling, carpet, or linoleum is scheduled an additional sub-floor layer is required. In areas scheduled to receive hardwood or equal, the 1/2" subfloor is more than adequate. I have had a 1/2" subfloor is my past three houses due to the fact there was a hardwood floor finish over it.
3) Is it still allowed in new construction today? Table R503.2.1.1(1) of the 2003 IRC states that 7/16" plywood with a span rating of 24/16 is permitted to span 16". Per that same table, 3/4" only becomes required when the joist spacings are 24". So, to answer the question directly. YES, it is allowed by code, at least here in CT.
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Old 12-22-2011, 08:14 AM   #14
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I am so confused.....
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Old 12-22-2011, 08:23 AM   #15
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Replacing underlayment in entire house...what material to use?


Bud & OP, I'd say go with 3/4" T&G screwed down nice. That will appease all here and will give you a solid floor do anything you wish upon...

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