When installing hardwood floors, should I use rosin paper, roofing felt, or nothing underneath? Why?

Question

I've installed hardwood floors, over top of OSB subfloor with a layer of roofing felt in between. I copied this from the hardwood floor contractor who did a kitchen in my home once. He'd been in business for 20 years so I trusted him. I think he said it was to prevent squeaks.

Is this true?

Does roofing felt used in this way also provide a vapor barrier, and if so, why is that important under hardwood? I can understand why it would be useful on a roof. I can understand why it would be useful for housewrap. Under a floor?

I read elswhere that rosin paper was originally used to keep floors clean (protect from the dust from drywall finishing, for example), and make it easy to slide floorboards. That seems pretty minimally valuable. Do I care if my OSB gets dusty? I usually shop-vac the OSB before laying down the floorboards, so is this really a benefit? And using rosin paper to ease sliding boards during install? Really? I never noticed a problem sliding the boards. Is this because I'm really strong? (not likely). Maybe it's because I'm using OSB as a subfloor which is a pretty smooth surface? I can imagine using plywood as a subfloor, in the days before OSB, might/could cause hitches when sliding boards during installation.

Do either of these layers provide sound-deadening or anti-squeak qualities? I figured the lack of squeaks was from using a sound, level subfloor, and installing the T&G tightly.

This question gets asked a lot in various DIY or even contrator forums. The problem is, there doesn't seem to be a general convergence to a single answer.

Answer 1

OK here we go. First of all, the most common reasons for squeaky hardwood floors are age and installation over uneven subfloors, where any movement of wood on wood makes the sounds. Age becomes a factor when the subfloor ages, shrinks a bit making the nails holding the hardwood a bit loose. Adding either a layer of felt or rosin paper isolates the wood layers and helps to minimize squeaking wood to wood. A lot of the squeaking on older floors are actually the nails moving in the subfloor, so today we use threaded nails, and for the most part and that solves that problem. So in your case, it certainly can't hurt to use some paper. Good luck.

Answer 2

Generally wood flooring these days is laid on a 3/4" plywood subfloor, whereas in the 50's and 60's a subfloor was 3" by 3/4" planking. Rosin paper would block light from the basement shining through the floorboards. I personally no longer use rosin paper on wood floor installs simply because I like to use adhesives on miter cuts used for perimeter picture frames and inlays. I find no sense in gluing wood to paper.

Answer 3

Mike Holmes says he uses it for mostly to keep dust down and to make it a little easier to slide the boards. He also says it is definitly not a vapor barrier since you make hundreds nail holes through it.

Answer 4

Rosin and felt are merely air blockers. They let moisture pass through but at a slower rate. Hardwood flooring needs to expand and contract with the house. Moisture or lack of moisture is what make the wood expand and contract. The problem is when there is too much moisture. And in my opinion, the only way to prevent floor squeaks is deck screws.

Answer 5

I always thought that the felt paper under floors was for water retention, and so you couldn't see any light coming from the floor below. For example I have two horror stories from living in apartments that were T&G floors without a felt paper barrier:

1. An upstairs neighbor had a nasty habit of spilling drinks on his floor. Every time there was more liquid than the floor could wick up, it would leak right through to my ceiling. Eventually there was considerable damage to the ceiling, not to mention to my valuables below. Once the ceiling fell, I could see light coming through the small cracks between each board.

2. I got an apartment that was right above the laundry room, and the only bedroom was right over the light for that room. At night when people would do their laundry, my floor turned into a planetarium. The rays of light were small, but they were enough to be a real nuisance.

Those were both buildings built a long time ago. And I will admit that felt paper sheets rolled onto a flat floor can be anything but waterproof. I'm betting that the newer materials that you are using will be plenty to prevent any light coming through from an unfinished basement, but what will happen to any liquids that get spilled on the floor above? Do you want the flooring to sit in the water or do you want any liquids to just pass through to the other areas?

Answer 6

If you nail the floor securely to the subfloor using helical or "threaded" nails, you shouldn't have a problem with squeaks. An underlayment under solid floors is nearly always to restrict moisture transfer, not to prevent squeaks. As auujay (and Mike Holmes) said, nothing you put a bunch of nails through will be a 100% impermeable barrier to water; the object is simply to minimize the transfer of water.

The most common material nowadays is Tyvek, also sold as TyPar; it's a polyethylene plastic mesh that is water-resistant, but breathable, so liquid water can't get in, but air (and any water vapor it carries) can, allowing the wood to "acclimate" to changes in humidity without being at risk for real water damage. The older materials, such as tar paper and roofing felt, will do a similar job, but they're generally thicker, heavier, more costly and/or break down faster.

Answer 7

I'm in the process of installing engineered flooring in my house. Upstairs when I started, I skipped doing the rosin in two rooms but put it in the master room. What a difference it makes in noise. Floors are being nailed down with staples and I though they wouldn't move against the sub floor at all. When walking in the rooms that don't have the paper I do hear the floor rub slightly against the sub floor but I don't hear that in the master.

Downstairs I'm in the process of laying the floor there and have rosin paper down the living room and tar paper in the kitchen. Using tar paper since there is a much greater chance of moister variations in the subfloor there and reducing that transfer to the wood floor.

One section of my house is on slab and that area is using a foam pad with vapor barrier, but the floor there is floating and not nailed.

Answer 8

Funny, I was told to use roofing felt and never even questioned it. Probably because it was relatively cheap and easy to do. I think I was told it was to prevent squeaks. But thinking about it now that doesn't really make sense as floor squeaking is caused by the flooring (or subfloor) moving up and down against a nail, not by the floorboards somehow sliding across the subfloor. If anything, having a somewhat resilient layer between the boards and the subfloor would slightly increase the likelihood of a squeak developing, wouldn't it?

Answer 9

None of the above. You should be using a pad designed for flooring; it prevents squeaks, insulates your floor and on the higher end pads, has a moisture barrier built in. The padding is more expensive but worth it. If you decide to go without, silicon paper is the minimum underlayment you want.