On the top side of the floor another fix it idea to lay down new hardwood over the existing floor.
Cutting door into lower level floor.
Mark any concrete bumps that are raised above the rest of the floor with an x and any dips that are lower than the floor with an o.
Strip the frame down to the side 2 by 4 inch studs top header plate and floor or subfloor.
Check the marks with a 4 foot level to ensure the lines are plumb and level.
Leveling a floor can be either a do it yourself project or a job for the pros.
Lay a long level downhill on the floor with one end of the level on the level part of the floor and the other end at the lowest point.
Hold a 16 inch long two by four block of wood vertical 4 to 5 feet up and centered in the doorway that will be cut out.
Drill two or three holes through the wood and into the foundation material with a hammer drill and a 1 4 inch diameter masonry bit.
A plywood subfloor will bridge any minor waves in the existing floor and leveling compound would help too.
You will have to make sure your joists can handle the addition of considerably more weight from the plywood subfloor and any floor coverings.
Determine the underlying problem.
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.
Shop made sanding block to chamfer the cut edge of the door make a sanding block by cutting a 2 by 3 4 inch strip of wood 1 2 inch shorter than the diameter of the peel and stick sanding paper.
Use a piece of chalk to mark all obvious high and low spots on the floor.
Cutting a few inches from the top of the existing joists.
Before taking steps to level a floor you must find out why it s not level.
In these situations lots of builders take the approach you mention.
Remove any old door and molding such as a casing or bottom threshold inside the opening.
Glenn mathewson a code official in westminster colo responds.