I have been re-doing my youngest son’s room, and just got to the floor. I removed the ugly linoleum put down by the previous owner. The sub floor is not level. The high point is 3″ from the bottom of the wainscotting I put up. From there the floor varies, from being off by 1/8 of an inch to up to 2″ lower than the high point. This measurement is not consistent all the way along the same wall either; on one end of the wall it is off by 2″, but by the time it get to the other end of the same wall, it is only off by 3/8″

I have been told to: a). use self leveling compound, which I do not want to use on a 14′ by 16′ room; 2) shim where it isn’t level, using either pieces of wood of different thicknesses, then installing a new sub-floor over that; c) build up the non-level areas by using roofing shingles or builders paper, or d). remove the sub-floor, and sister new joists to the old ones, to make the floor level.

The last choice sounds hardest, but also like it will be best in the long run. Has anyone had this problem before, and what do you suggest? The house is 150+ years old. I have put laminate flooring down on 2
other floors, and neither have been off by as much as this room.

First step for me would be a survey UNDER the joists to see if lolly jacks or other support is needed. Find out where the problem originates.

Your post indicates you are working through the entire house, this might be a better starting place for the remodel. Some of the previous modifications could be such that leveling out one area will affect another. Also check your mud sills while you are downstairs. Unlikely to be treated wood and if they need work also, you are much better off to start at the bottom and proceed upwards. [exception is leaking roof, prevent further damage first]

Of your listed options, the sistering is best as you surmise and maybe not the hardest when all items are considered. Removing the present subfloor is probably the worst of that. If there is a place to set up a laser level the joist replacement would be rapid and give you a solid level base to work from. The shingle/building paper would be the worst results within a very few years as it compresses.

Combining your a and 2 would be workable. Shim to give yourself level spots to strike the compound. However, this might be enough weight to affect your flooring even worse. [see above comment about basement.

I should mention that the bedroom is on the second floor. Under the sub floor is more than likely old plank floors. In the living room there were wide planks under the carpet. Some of the planks were uneven, handmade nails had popped out, etc. Once the boards in question were fixed/replaced, there it was level. I am hoping that it is the same in this bedroom, that it is the planking underneath that is uneven. No, no dry rot or termites, sorry! And yes, we’ve already jacked the house, and started at the bottom, including jacking, foundation repair, entirely new heating and electrical, etc.

I suggest an inspection, whole house. You may have problems which could result in the house collapsing at some point.

While redo-ing the kitchen we had this problem, we pulled up the subfloor and found termite damage in the original hardwood floor. Thankfully, the had been long dead, but the damaged really bugger up the floor. So we removed it to just start over, from “scratch”. We found the beams underneath to be “rough-cut”, not in the least bit level! Sigh! The hand planer came out of the box again!

You seem to be checking floor level against the stuff on the walls. Have you checked the floor with a carpenters level. The floor might be level but the stuff hung on the wall may be off. I always try the simple solution first then go to the more complicated.

Well, when I installed the wainscotting, I determined a height, made a level area in the center of the floor, which I checked with the level. Then I used the laser level at the height I wanted the wainscotting. Used the plumb bob to snap a chalk line on top of the line the laser level made, then checked that with a level to make sure it wasn’t off, which it wasn’t. Each piece of wainscotting was also checked with the level as it was being installed, then when it was completely attached. So, I am reasonably sure that the stuff against the walls is level.

Besides, it’s really easy to tell when my son’s hot wheels, trucks, etc roll to the same corner of the room unassisted! Seeing as the baseboard is removed, I stuck my hand down between the wall and the sub floor, and found there are 3 separate floors down already. It seems to be 2 layers of plywood sub floor and one layer of plank floor on top of the joists, from as far aa I could get my hand in. That was on the section that it is off by 2 inches. It looks like the top layer of sub floor is not exactly square.

I Didn’t mean anything mean by my comments about checking the floor with a level. I didn’t know you installed the wainscoting using a level. You apparently know what you are doing. I have friends that don’t even know what a level is let alone own a laser level. I always like to start at the basics then work from there. Wow if you sons hot wheels will roll across the floor unassisted its pretty bad.

Now I have a question for you. Why did you do the walls before leveling the floor? Seems easier to work on the floor before you have nice new walls to worry about. If you really have 3 floors I would tear down to at least the first one and start from there. You could even tear out the 1st floor so you can get to the floor joist and shim them up to level the floor or level a 2nd floor over the first one. Or leave it un-level so your son doesn’t have to set up a hot wheels track to play with his cars.