Strange Floor Assembly
Hey everyone,
This site has been so helpful for my strange reno/build Qs.
So here is another!
We have a bit of a strange floor assembly. It’s a 1950s classic split level. Subfloors were in pretty decent condition throughout. We replaced a few pieces here and there and screwed down the remaining board. However, we were not satisfied and wanted a stronger and more stiff profile and added an underlayment. So we did some research and came up with this.
NEW 1/2 inch plywood layer
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Rosin Paper stapled down to old subfloor (to prevent squeaks)
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Old plank subfloor
However, we are now doing our flooring and going to use 3/4 hardwood planks. The subcontractor wants to put some type of underlayment under the hardwood itself.
So this is what our entire floor assembly would now look like:
3/4 Hardwood Planks
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Some form of underlayment
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1/2 inch plywood layer
Does this make sense? What would you use as underlayment for the hardwood? Quiet walk was recommended but Subcontractor is concerned it will have a softer feel.
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Replies
Is the new plywood already there?
If not, probably not needed with the new 3/4"
If yes, I'd confirm the structure can support all that dead load.
The 1/2 overlay is very common with older plank subfloor. I don't see any issues with your setup. Just do the future a solid and don't put it down with 3" spirals, I had to pull up about 100sqft of that a while back and was cursing the original installer the entire time.
The sound improvement from any of the underlayment is way overestimated in a stick framed house, from my experience they do squat. They do work really well over a concrete floor.
I would use something cheap to limit squeaking, don't really matter what.
Akos,
Almost straight out of architecture school with next to no practical experience, my wife and I built a house. We hand nailed the sub-floor with 3" galv. spirals. I think my wife has forgiven me. My elbow hasn't.
Yes! We used 1 1/4 inch screws that would only slightly penetrate the old subfloor from new plywood. We were advised not to screw into joists directly.
Is there a good moisture proof underlayment that you've seen? Something non toxic too, want to stay away from asphalt etc.
There are some foil faced underlayments made for this purpose that are two foil layers sandwiched around a maybe 1/8" or so layer of dense foam. They claim about R1 of insulating value (better than nothing :D), a slightly softer feel for less stressful walking, and a moisture barrier IF you tape the seams. Cali Bamboo's Calicomplete is one such offering, but I'm sure there are others.
Bill
Which direction are you trying to keep the moisture from moving? IE, from below up or from above down? If you're trying to protect against a damp crawlspace the vapor barrier has to be below the joists, otherwise they will rot.
Not also that "moisture" is a bit of a confusing term. There are a lot of things that are impervious to liquid water that let water vapor through. Most waterproof paints, for example.
This will be an underlayment for hardwood floors throughout the house. Ideally, we have a basement with dehumidifiers running constantly. In addition, the kitchen will have hardwood as well. We've made some good thoughts on reducing any type of water intrusion from above the floors, no water line to fridge. Leak detectors under cabinets, and pans for dishwasher.
Unless your lower level is closed off from the main level and is unusually damp, there is no need for an underlayment membrane. It does nothing to prevent squeaks, which is the main reason people (including many installers) insist on using it. (Same for rosin paper between layers, sorry to say, though someone is likely to disagree with me.) But they don't do any harm so I've stopped trying to convince contractors otherwise on my projects.
That said, if your house is like my old split foyer, with a garage under the living space, or if your lower level is just damp and you don't want to address that (though you should), you could use what I used on one project: https://www.robertsconsolidated.com/products/silicone-moisture-barrier/. That one was a renovation on a house built on piers so there was high risk of the flooring cupping due to differing moisture levels on each side of the flooring.
How different is that stuff from a regular sheet of polyethylene? It looks like white poly, but says it has a "silicone coating", so I'm guessing it's a bit grippy? Just curious as to your experience using the product.
Bill
It's a heavy paper coated with silicone. I'd say it's somewhere between kraft paper and poly sheeting in grippiness/slipperyness. They don't share their perm rating but claim to meet the NWFA recommendation of 0.7-10 perms.
I would NOT recommend using poly sheeting as an underlayment. If fact, on the job I mentioned, when the plumbers were doing their final testing they left a faucet running and it overflowed, flooding the floor. We addressed it with fans, heaters and dehumidifiers as soon as we found it and the flooring dried out with no problems. I don't think that would be the case with an impervious underlayment.
So what does everyone think on an underlayment given this sandwich? Is rosin paper fine? I think he brought some rubberized materials which was really thin. I don't want to overthink it either, as I've had decision fatigue up to this point. But want something that will stand up to time.
As long as the underlayment is 0.7 perms or higher, it should be fine. Rosin paper was originally used to block or slow air moving from below. There are claims that it stops squeaks, but squeaks come mainly from wood sliding on nails, which rosin paper does not help, or from wood sliding on wood, which doesn't happen between wood flooring and the subfloor to a large or fast enough degree to create squeaks. It also does nothing to block vapor drive. I have stopped trying to convince people not to use it; it's harmless. Same for synthetic underlayments meant for the purpose. If they want to use them, let them.
Have you ever used this one?
https://www.homedepot.com/pep/ROBERTS-Silicone-Moisture-Barrier-200-sq-ft-31-5-in-Wx76-25-ft-L-x6-mil-T-Underlayment-for-LVP-Solid-Engineered-Wood-Floors-70-198/205129063?mtc=SEM-BF-CDP-GGL-D23F-023_011_LAMINATE_FLR-NA-NA-NA-DSA-NA-NA-NA-NA-BT3-NA-NA-NA-LAMINATE_FLR_DSA_G&cm_mmc=SEM-BF-CDP-GGL-D23F-023_011_LAMINATE_FLR-NA-NA-NA-DSA-NA-NA-NA-NA-BT3-NA-NA-NA-LAMINATE_FLR_DSA_G-71700000102202228-58700008155069614-39700074103020805&gad_source=1&gclid=Cj0KCQiAire5BhCNARIsAM53K1idFWOhQRU2ZHuKI7URm7Ha3Egc0QhVj0BbdVG-WOas4kcKg7rkR8waAmA3EALw_wcB&gclsrc=aw.ds
Again, with our assembly of
(Basement)
(Old plank subfloor)
(Rosin paper)
(Layer of plywood)
(Underlayment)
(Hardwood)
I'd just like for things to dry appropriately and nothing to get trapped. We spent the better part of 13 months building this crazy home. It might be important to note that this hardwood will be under a kitchen too. But we've made precautions such as
No water line to fridge
Special pans under dishwasher
Leak detection under sinks.
I have often found floor squeaks to be from nails in the bottom plate of nearby walls, not the subfloor-to-joist nails you'd expect. A long construction screw or two run in diagonally from behind the moulding is usually enough to stop those squeaks. All you need to do is stop the movement along the fastener to prevent squeaking.
Bill