Leveling a Bottom Plate on an Uneven Floor

The bottom plate is the horizontal piece of wood at the bottom of a wall to which all of the studs in the wall are attached. It's important that the bottom plate is flat, because if it's uneven, the top plate, the horizontal piece of wood to which the tops of the studs are attached, will be uneven, too. Making the bottom plate flat is easy on a flat floor, but if you're building a wall on an uneven floor you'll need to do a bit of extra work.

4-foot level
Cedar shims
Hammer
Handsaw

Instructions

- 1
  Lay a 4-foot level on the floor directly in front of the bottom plate. Look at the bottom edge of the level where it meets the floor. Any gaps between the bottom of the level and the floor indicate low spots in the floor.
- 2
  Tap wood shims in between the bottom plate and the floor wherever there is a low spot in the floor. You can use cedar shingles for shims, or buy purpose-made shims that are essentially the same thing as cedar shingles. Insert the narrow end of a shim from both directions so that the shims overlap each other underneath the bottom plate. This gives the wall more consistent support than if you put just one shim in. Tap the shims in at the same time until they are very tight between the bottom plate and the floor. Don't tap them in so far that you start to lift the wall.
- 3
  Trim off the parts of the shims that protrude from under the wall using a handsaw.
- 4
  Check the straightness of the bottom plate by eyeing it from one end with your eye next to the floor. If it isn't perfectly straight, put in more shims under any remaining low spots.

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