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wood floor installation questions

After I teared up my carpet and pad of the first floor, I found many moister steins on plywood subfloor. This is a 23 years house which I bought 3 years ago. I don't know what happend before. The basement underneath is try. In damp weather, I just turn on dehumidifier occasionally. Maybe the vapour can penetrate the subfloor and trapped by the pad and cause steins. Actually I don't care about the reason much now. I just seriously care in this situation, can I install solid hardwood floor on the first floor? If yes, what kind of underlayment should I use? Still go #15 felt paper or rosin paper?
Sure, I will not turn off dehumidifier in damp weather if solid wood floor is installed. My next 2 questions
are about the level issues. The subfloor is 3/4" plywood T&G. But when the previous owner installed the ceramic tile of hallway, he put another 3/4" plywood on subfloor. So now the surface of hallway tile is 1" higher than the family room subfloor. When the ceramic tile was installed in kitchen, the old vinyl tile wasn't removed. Another 3/4" plywood was put on it then installed ceramic tiles. So the ceramic tile surface of kitchen is more than 1" higher than the family room subfloor. I plan to put a 1/4" or 7/16" OSB on subfloor then nail down the solid hardwood floor. Can I put those kind of thin OSB then nail down hardwood planks? No matter what kind
OSB I choose, I can only eliminate level gap of one end, there is still a small gap at the another end. What's
the minimum gap of level acceptable if I use the T-modeling to cover the expansion gap between tile and hardwood floor?

Re: wood floor installation questions

first things first, the dampness issue should be addressed, hardwood flooring and moisture dont mix. the hardwood will swell and buckle if its not tended to correctly

as for the height issue. measure the height of the ceramic from the old floor sheathing, next subtract 3/4" from that which will give you the thickness of underlay you will need. dont use thin osb its less stable and gives less holding power, go with poplar underlay, glue and ring nail the snot out of it. as for paper, if there is a dampness issue #15 felt will help but simple rosin paper which is kept in the flooring section is the standard

as for the trim piece to make the transition from tile to hardwood, if you cant a get a piece of metal that works, simply make one out of 1/2" hardwood on a table saw or get someone to make one, most common is a 3" wide piece with a 75" bevel put onto it leaving around 3/16 at the edge, put it down with construction adhesive and have it cover the gap between the different floors

Re: wood floor installation questions

Besides roof, 3/4" osb is also widely used as subfloor. I don't understand why I can't add 1/4" osb on the top of my subfloor. Will it create any power problem?
Regarding moisture control, do you have any suggestion?

Re: wood floor installation questions

for the moisture problem, i believe you said theres a crawlspace below, if you can get down there, pick up some tyvek or typar and install it to the bottom side of the floor joists, this product will keep dampness out but let the floor breath

as for osb for the floor, yes it is very widely used however it isnt as strong a product as plywood, 3/4 is used quite extensively in production housing as builders put the houses up as cheaply as possible, custom and high end builders use plywood and save the osb for the walls and roof. one of the biggest differences being in fastener holding power.

1/4" osb is almost never used as an underlay, it has no strength and has no fastener holding strength. 90% of the time if you see it in a house on a floor its as temporary protection for floors during renovation. 1/4" poplar or doug fir is the industry standard for underlay

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