But older homes frequently have subfloors that are out-of-level creating sloping floors.
Even some newer homes already have uneven subfloors.
How can you correct an uneven subfloor before installing flooring so you have a level floor?
The Spruce / Jacob Fox
The subfloor is a structural component, essential for the strength and durability of the home’s flooring platform.
This subfloor layer must be stable, solid, flat, and level.
For example, ceramic tile installed over a bad subfloor can result in cracking grout or broken tiles.
The Spruce / Jacob Fox
While there are several ways a do-it-yourselfer can fix minor irregularities.
Butlarger sloping and sagging issuesare beyond the reach of most do-it-yourselfers and typically involve leveling uneven floors using jacks.
Look for gaps between the bottom of the straightedge and the floor.
The Spruce / Jacob Fox
This means you may need to reinforce that joist to get to correct the floor sagging.
The short sides of the plywood sheetsmustbe centered over joists to support the ends.
Plan the layout so there are 1/4-inch expansion gaps at the walls and between sheets.
The Spruce / Jacob Fox
Place the first sheet into position along one of the walls with a 1/4-inch gap along the edge.
If attaching more than one sheet, trim as needed and place the next sheet in the first row.
Leave a 1/4-inch gap between the ends of the sheets.
The Spruce / Jacob Fox
Fasten the second sheet as with the first.
load the remaining sheets in the first row, trimming the last sheet to fit, as needed.
double-check to leave 1/4-inch gaps between sheets.
The Spruce / Jacob Fox
Leave 1/4-inch gaps between all sheets.
Continue installing sheets of plywood across the room, attaching them to the floor joists in the same way.
confirm to maintain 1/4-inch gaps between the sheets.
The Spruce / Jacob Fox
Fill Gaps
Mix self-leveling compound and trowel the mixture over the seams and screw heads.
Allow the self-leveling compound to dry, then sand the seams and nail-heads smooth.
Vacuum the entire floor before proceeding with the new floor installation.
The Spruce / Jacob Fox
When mixed with water, the compound settles into low areas and dries to a smooth, level surface.
Self-leveling compound comes in large pre-mixed buckets or in dry form that can be mixed with water.
A long straightedge works well to identify these low spots.
The Spruce / Jacob Fox
If the manufacturer recommends it, apply a primer to these areas and allow it to fully dry.
You may need to temporarily remove any cross blocking to make it move the sister joist into place.
A contractor, in consultation with a building engineer, is usually the best option in such situations.
The Spruce / Jacob Fox
The cost depends on the scope of the project.
If you are very lucky, you may only need to use aconcrete resurfacing product.
Although no subfloor is perfectly level, you should always venture to get it as perfectly level as possible.
The Spruce / Jacob Fox
This is important especially if you are installing very thin, flexible flooring likeluxury vinyl tile (LVT).
