My home, which is about 40 years old, started as a one story home. Some years ago, a second story addition was built on top of the existing roof. Every thing seems structurally sound. However, the floor is not level. It has the pitch of the original roof (1/8 inch per foot) left the floor unlevel.

The master bedroom is 15 x 20 feet, so the drop is noticeable - about 3 inches.

I want to level the floor.

What are my options. I was considering

1. Pulling up the plywood flooring, then sister nailing 2x8's to the existing 2x12's to level the floor, then replace the sheathing.

2. trying to cut a 2x6 (20') on a diagonal. A lot of work and difficult to nail to the existing studs without splitting the wood.

3. Nailing sucessively thicker strips directly to the existing subfloor (opposite direction of the joists) 12 inches apart then add a new plywood subfloor to this.

Give me your thoughts on this one.

Is there more to it then just the master bedroom? Are you planning on leveling the entire addition?

Are there any interior load bearing walls? If so ate they supported enogh underneath ?

I already leveled the masterbath - so the only thing left is the bedroom. It opens to a 3x3 foot landing which enters at the high end - so that will be easy to fix.

How are you going to address the doorways? If there is no sign of settlement, my guess is that they had the building erected that way and with a flat roof is not much slope. Personally I'd go with a diagonal 2X4 except finding a 20 footer is hard. Use 2@10ft. Cut 3>1.5 and then 1.5 > nil. Use construction adhesive for the glue down and you won't have to nail at the thin edge. Then recover with plywood or OSB. I use this technique in walls but have never done this scale on floors. Let us know what you decide and how it turns out.

I would go with option 1 and sister nail to the existing joists. That way you get as long of a run as possible.

I'd go with tapering some 2 by material to attach to the top of the existing joist. Certainly it will take some work, but a lot less than trying to build up with plywood or filler material. A lot less costly also. Tapering a 10' 2x4 from 0 to 1 1/2" would not be all that difficult if you have a good table saw and take the time to build a temporary saw fence. You would have to have a lot of room. You would need 10' in front of the saw and 10' in the rear of the saw. Probably take you a Saturday morning to machine all of the material you would need. Take a lot longer and be a lot more frustrating to try to build up the low end. Too difficult to find material of the correct thickness.

If the total distance is 20' and the total drop is 3", a 10' 2x4 ripped from 0 on one end to the center on the other would make two pieces of material to be attached to the top of existing joist. The tapered joist can then be glued and nailed. Another 2x4 ripped down the center can be glued and nailed to the low end of the span, then attach a tapered piece on top of that.