If you have access to the basement or crawlspace it is possible to jack up saggy joists until they are level and then sister them so that they remain straight after the jacks are removed.
How to level existing floor joists.
A plywood subfloor acts as a bridge for minor waves in the existing floor as well as a leveling compound.
Even though we use 1 pt lumber the joists are often slightly warped or vary in depth at times causing adjacent joists to differ in height by as much as 1 2 inch or more.
Fixing a floor that sags and dips pour self leveling underlayment in the problem area.
Then use pry bars and your reciprocating saw to pry and cut the floor joist away from the subfloor.
Depending upon the conditions it is possible to strengthen or repair existing framing members such as floor joists or roof rafters by adding reinforcing material sandwiching the member on either side with plywood is sometimes worthwhile but the plywood must be installed correctly for greatest strength.
If you suspect that you re working with an off level foundation you can get it ready for installation quickly by using a floor leveling compound.
Pry the floor joist from the subfloor with the back of your hammer.
Then a string line can be fixed to the top of these two new joists giving you the level for the joists in between.
You can then smooth it out using a hand trowel and sand the entire surface for a seamless finish.
If the uneven floor is due to floor joists that have warped or twisted over time or were incorrectly installed the only way to level the floor is to remove the subflooring and shim the joists.
Only raise the jacks about 1 8 inch per.
To level the entire floor it is best to start with the two end joists.
Compound can correct sags and dips as deep as 1 1 2 inches.
Place two hydraulic floor jacks under the 4 inch by 4 inch post and raise the post until it contacts the floor joists.
Raise the lower end of the level until the bubble is centered then measure the distance from the bottom of the level to the floor to find the depth of the dip.
This will create a weak spot.
Simply mix up the compound pour it over the subfloor and wait for it to fill in the lowest spots.
Setting the joists perfectly level at the house is easy and the beam makes them fairly even near the front edge but the problem is in the middle.
You can also lay down new hardwood floor on the top side of the floor.
Start by cutting out a small 1 2 in 2 5 5 1 cm section of the floor joist with a reciprocating saw.
They have a strong lip which is then inserted into a brickwork joint or fixed on a timber or steel support.
Raise the jacks about 1 8 inch more.
