As an experienced homeowner, I will be installing an unfinished white oak strip floor (2 1/4 inch width) over 3/4 inch T&G plywood. I have previously installed wood floors over 15-lb felt, as manufacturers and NOFMA recommend. I don’t see the point of bothering with felt paper, at least in terms of vapor retardation, because the 3/4 inch ply has a permeance rating of only about 10% that of the felt. Plus, the felt wrinkles up, stains the bottom of boots and therefore new and old floors in the house, etc. I wrote to NOFMA with the idea of omitting felt and the response was basically that my attempt to compare the vapor transmission (permeance) of plywood to that of felt paper was like comparing apples and oranges. I don’t know why. Do I look like I have “stupid” written on my forehead, as they say?
I have also been told that the felt may be more of a problem than a help in hot conditions with potential bleeding of gunk through the floor. This is probably why NOFMA does not recommend its use in radiant floors. All that said, what are the experiences of those who have installed a lot more floors than me? If it matters, the floor is over a crawlspace with dirt floor covered with 10-mil poly, so moisture is allways of at least some concern, still, why isn’t the plywood enough to control moisture….??
Thanks.
Replies
I'll be interested in the responses you get as well. I'm close to ready to install oak over radiant heat and I've done a little bit of research. My understanding is that felt is used more to reduce squeeking from the oak and ply rubbing against each other. It does have some vapor-related benefits of slowing down the movement of moisture but I don't think they really consider it a vapor barrier. I also think that the reason they don't recommend felt over radiant heat is because the paper might generate some odors when it's heated by the radiant.
Roger
No longer aka Nostra Dumbass...
I have since talked to several folks locally and they seem to agree that felt is not worth it, esp with radiant heating. both smell and actual oozing of asphalt can supposedly be problems. Good luck. I'm still not sure about my situation since NOFMA's position is that felt is vapor barrier and plywood is not.
Bob
I have laid many strip floors over plywood sub-base, but in Australia, where it is not usual to use a felt (or indeed, any) underlay.
The flooring is secret nailed with a bead of construction adhesive at 12" centers and I've never had problems.
As to the coating, here is a site that gives very good advice.
IDG
thanks. I checked out the sites and got a few more good ideas.
What's the thoughts on red rosin paper? Jeff
* Jeff J. Buck/ Buck Construction/ Pittsburgh, PA *
2nd Generation Buck Const, 3rd generation Craftsman
Red rosin paper was quite common and still is amoung some installers as a floor underlay paper.
It serves the original purpose of air infiltration and as a lubricant to reduce squeaking admirably without the off-gassing and other problems associated with a hydrocarbon product.
I also spoke with the the wood floor association people on several occassions as to why they no longer reccommend rosin paper and have yet received any real answer. Comparing apples and oranges? That is correct. Plywood is a much better vapour retarder than felt ( felt is not a vapour retarder and will pass vapour)
Problems of moisture from below the subfloor need to be addressed there and not at the finished floor level regardless of what one uses.
I realize many installers rely on construction adhesive for floors, however I choose not to. I use red rosin and either blind nail or face nail depending on flooring. I see and have been shown no reason to do otherwise
david
walk good
I read/heard/whatever that the original purpose of the felt or paper was to keep coal dust from coming up from the cellar, so I omitted it from the last floor I laid (3/4" red oak, unfinished) with no apparent problems.
We put flooring over felt or rosin paper for the simple reason that the customers expect it. A lot like 15# felt under the shingles on the roof. I can think of a lot of theoretical reasons to go either way but I don't think that it makes a lick of difference in reality. I've never noticed any difference in the finished product.
I agree that moisture problems from crawl space need to be addressed there. I have also been told, however, that the felt helps to equalize moisture absorption between top of wood (typically finished with poly or ?) and the bottom of the flooring, which is unfinished. In this case, it seems like moisture in ambient air might be a problem, and one installer locally here told me he uses felt only in houses near the ocean. This is apparently just another case where there is no single right answer that always applies...
I always use #15 felt under my floor builds. If for no other reason it makes for a nice clean surface to work on and allows us to rack the floor faster. The boards also slide better and don't hang up on overwood at the ply seams. I do believe it slows moisture migration and acts as a gasket between the sub floor and floor boards, helping the floor to build tighter. We also take time in aligning the paper to our straight edge and use the reference lines on the paper to insure our runs are staying straight.
Thanks for advice. I have since been told and have read that most so-called 15-lb felt is not really 15-lb felt anymore. As a result, the thinner stuff tends to wrinkle more. I have a local supplier who stocks the "real" 15-lb felt and he says that it lays flatter than the thinner stuff. Perhaps that will help with my wrikling problem that I had before.
Bob,
Do not use tar paper in a radiant floor. No. Do not. Nada. Nope. Don't do it.
You're right that "15-pound" felt doesn't weight 15 pounds anymore. If you really want to get into it, they even changed the name of it. It used to be "15#", or 15-pound" felt. Now, it's "#15", or "Number 15" felt. those sneaky marketing guys. Today's #30 felt is closer to yesterday's 15#.
If you don't want to use felt, use red rosin paper. Under strip flooring they are interchangeable.