i'd like to level them from the floor joists, not adding another floor over the existing ones
To leveling a floor first choose one room then by strain level from one side to other make a level line or use a long level ,you will see 2 condition as possible 1- Level 2- Up and down in second mode you have 2 choose 1- Grind the high joist 2- Fill the gap by adding the thin shims on top of the lowest joists and then cover the floor by ply wood .
leveling the floor can be involved but it is not very complicated . As it is a sign of something settleing in the house you can look for signs of foundation problems .You can also level the floor by sistering new joist onto the old ones or as simple as cutting tappered shims the lenght of the joist and than fasten them to the top of each joist to level it . than you can install your subfloor and be on your way . As for the problem with contractors it seems many people have some dilusional idea of what it takes to accomplish the task at hand . the real world isn't the DIY network or the home makerover show .If people realised how much those projects on tv really cost they would be amazed. and many people seem to hire the cheapest guy they can find , there is usually a reason why the contractor is much lower than anyone else , You really do get what you pay .
I will assume you have some low spots, and not an over all slope to the floor. In this case, and if you have access to joists under the floor, you can tap shims in between the joist and the underlayment plywood. tap the shims in until the area comes back to level. You will want a helper with a level upstairs to tell you when. If the whole floor is sloping, you may have a foundation problem. At any rate, you will need to re-level the house with house jacks. This is not too difficult to do, but you need to be very careful with the plumbing and electrical connections. You may also have to deal with tie downs depending on what part of the country you are in, or what kind of home you have. For this reason, if you need to level a house it is best to hire a pro.
Assuming you have a basement with a good floor, (I did) I used 6, 4 in I beams 10 ft long. That is all I could handle by my self. 13 screw jacks. The 7 ft ones. I spent the biggest part of a year, I would screw us the lowest ones till the old house started creaking and popping. Wait for a time, from a week to a month and go after it again. Took about a year. My house was 28 by 40, 2 story. As I leveled the down stairs floor the up stairs went along. My biggest problem was finding different doors. Over the years people had cut off the doors on an angle so they would open and shut. With every thing level and plum, they did not suit my wife.
start by removing all of your finish flooring and sub flooring. locate your highest point in the room. easiest way to do this is with a laser line level. you can set it up about 12-24 inches from your joists the measure up from tops of each joist in a few spots. once you determine the high point you will have to sister in new joist to the existing ones at this height using the laser line(you can also string lines if laser is not available. much more work) i would recommend using an adhesive like pl-400 and using deck screws to fasten your new joists. pl will prevent squeaks and screws are great fasteners for more accurate leveling. easier to back a screw out than pull a nail!!. so make a material list and get started!!! basically you will need same linear footage as you have already in your floor. make sure also your height will not become a problem with existing doors. Honestly unless you are putting a pool table in this room i dont see any reason to make a room perfectly level. its alot of work. i know this from many years of renovations Goodluck!!! if you have any other questions throught this process i can help you further just mail me !!!!
