Underlayment thickness

Tarawa86

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I'm installing hardwood flooring, and due to the layout of my living room I want to run it parallel to the joists. From what I've read/watched on youtube this means I need to install an underlayment over the subflooring - but I don't want to raise floor too high either. I have 16" joist spacing and a 3/4" subfloor.

Anyone have any experience on whether or not I could get away with using 1/2" ply for the underlayment? I already have the hardwood floor acclimating, this is sort of a last minute change of mind on my part.
 
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I've done close to a dozen flooring jobs in my homes over the years, running tile mostly and some of the fake hardwood.

You should have your floor joists, then a 3/4" layer of plywood, then a layer of thin waterproof underlayment, like tar paper or some specialty material. Not sure why you would need an extra layer of solid material unless the 3/4" layer is uneven.

I just remodeled a bathroom and stripped it to the joists, put down a layer of 3/4" plywood, 3/8" cement board, then the tile. Rock solid.

All you need to avoid is flex, and you shouldn't get any with a 3/4" layer of plywood on 16" joists. You could always throw down another layer of 3/8" plywood just to be certain.

I'll be replacing my main entry and kitchen floor soon with tile. I have 24" joists (ancient farm house) with original hardwood at 3/4", plus a layer of 1/2" particle board and vinyl tile. My plan is to rip up the vinyl and particle board and replace the particle board with 3/8" plywood, then 1/4" cement board, then the tile. Will have to raise the entry door, though. Probably.

I love home improvement projects!
 

ZigZagZeke

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I replaced 40 year old carpet and linoleum throughout the house with 3/4" hardwood (bamboo) and tile. The floor squeaked and flexed prior to the replacement. The joists are on 16" centers. We found that the underlayment was 5/8" plywood, probably the same plywood used when pouring the foundation, as it had traces of cement on it. We went back with 1" plywood under the 3/4" hardwood and the tile. No squeaks and no flexing now.

I would not go back with anything less that 3/4" plywood.
 
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I have the same thoughts as you OP, been eyeing some of the vinyl plank products at the big box stores. The only issue I have with increasing the underlayment/subfloor thickness is having to rip out all the baseboard trim and shorten the door trim/casings (and possibly the doors themselves) everywhere in the house. :(
 
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Tarawa86

Tarawa86

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Not sure why you would need an extra layer of solid material unless the 3/4" layer is uneven.
From what I've researched, it seems like you need to install a second plywood underlayment if you want to run your flooring parallel to the joists. It will save me quite a few cuts going parallel, and I think it will look better.

What type of hardwood floor are you installing?
Nothing to fancy, it's Bruce oak 5" wide product. I've been pretty happy with the low number of defects I've seen so far.

We went back with 1" plywood under the 3/4" hardwood
If you installed the 1" ply over the 5/8" subfloor, did you use the locking plywood?
 
How old is the home. What size is the floor joists and what it's made of and how long is the span. What is the sub floor material made of.
+1 -- critical questions that need to be answered.
Going over prior subfloor, never found the need for interlocking. However, used 1" sanded in an application once where I had raised a floor to level two rooms. After it was all said and done, I wished I had put sound deadening under the 1" -- it was like a sound board.
 

deadeye

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I'm installing hardwood flooring, and due to the layout of my living room I want to run it parallel to the joists. From what I've read/watched on youtube this means I need to install an underlayment over the subflooring - but I don't want to raise floor too high either. I have 16" joist spacing and a 3/4" subfloor.

Anyone have any experience on whether or not I could get away with using 1/2" ply for the underlayment? I already have the hardwood floor acclimating, this is sort of a last minute change of mind on my part.
So How old is the home? My floor is joists topped with 2x6 tongue and groove subfloor then 5/8 underlayment to cover possible uneven T&G to put flooring or carpet on. Are you sure the subfloor you are talking about isn't underlayment and there is another layer below? I know underlayment isn't always necessary and with newer homes probably not used often to cut costs.
 
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Tarawa86

Tarawa86

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How old is the home. What size is the floor joists and what it's made of and how long is the span. What is the sub floor material made of.
Appreciate all the replies.

The house was built in 1994, and I think the joists are 2"x10" with a span of 16" (if I understand the concept correctly) I probably should crawl under the house to check, but my extreme fear of spiders is holding me back somewhat. The plywood appears to be oriented strand - I measured the thickness via a random hole I uncovered.
floor.jpg
 

NCW_Robert

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Use what ever thickness of underlayment required so you dont have to replace the base boards. If a certain type is a little short consider some of the cushion type added right under the new floor. That could get you to the just right level on your base boards. If there is not floor squeaks now then dont worry about future floor squeaks.

Check bare floor height to base board every few feet all the way around the room, don't assume sub floor to base boards will be the same all the ay around the room, it should be but may not be and that will be good to know before you start.

Not an expert, only did a few floors but that is what I would do.
 

ZigZagZeke

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From what I've researched, it seems like you need to install a second plywood underlayment if you want to run your flooring parallel to the joists. It will save me quite a few cuts going parallel, and I think it will look better.


Nothing to fancy, it's Bruce oak 5" wide product. I've been pretty happy with the low number of defects I've seen so far.


If you installed the 1" ply over the 5/8" subfloor, did you use the locking plywood?
No, we ripped out the 5/8" plywood and put 1" plywood down directly on the joists.
 

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