I have a dilema that I have no idea how to fix. Here is a diagram of my houses layout...its a weak attempt at a diagram, but it gives you an idea.

|______________|
|______________|<addition
|______________|
|_-1/4_____-5/8_|
|______________________________|
|______________________________|
|______________________________|
|______________________________|
|______________________________|


The addition is 16wideX20deep (main house portion about 25x15), so tonight I finally got the point of measuring the difference in height for the subfloors between the addition and house. One side of the addition is 1/4" lower and the other side is 5/8" lower, those measurements are 6ft apart since the house and the addition are joined by a 6ft opening. So it seems either the addition or the main house is not level, knowing this house that does not surprise me.
The main house is 5/8" non-T&G and the addition is probably 3/4 T&G( i have yet to confirm)
The floors will be layed vertically in the diagram.

The question is how do I level it out to get them flat knowing its not level??

Knowing what type of installation you will be performing will help determine the best corrective action is.

Is there any way to get underneath the addition and possibly jack up one side really,really slow? This may not be feasible if the roof is already tied in.

Did you do this or a hired contractor?

Installing 3/4" BC.

We bought the house a month ago, the addition was put on 13yrs ago.

I can't jack the addition up, everything is tied onto the main house.


The only solution that I can think of would be to get the thinest plywood possible...3/16"?? and add layers to get it level, then add whatever thickness plywood on top to smooth it out. The main house will get 3/8 layed over top the existing 5/8" so I would likely put 5/8" TG on top of the layers in the addition to get it even with the house.
Feasible or not??

Thinking of another alternative. Previously there was carpet and a large transition between the addition and main house which is a 5ft opening and the transistion was wide since the dividing wall is concrete block. I could have a carpenter friend of mine make a similar transition of BC using some planks of hardwood.
It would certainly break the flow from one room to another, but might be a much more realistic way to solving this problem, what do you guys think?

Turns out I was wrong. Remeasured tonight using a level and its not off nearly as much as I first measured, only 1/8" over 6ft so I'm ok.

Good news! Glad to hear. You might look at this link to help with some of the subfloor imperfections you encounter.

www.hardwoodinstaller.com/hardwoodinsta ... r-prep.htm