How to Make a Wavy Ceiling Flat

Fixing a wavy ceiling isn't difficult, but it makes a huge difference in your home's appearance. Here's how to do it.

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Older homes, particularly those with plaster construction, may have cracked and wavy ceilings. If you install drywall directly to this surface, you'll still have a wavy ceiling minus the cracks. That's some improvement, but not enough to justify the effort.

The real solution involves the installation of furring strips—either wood or resilient channels. Find the lowest spot on the ceiling and shim all the furring to that point. It's not as difficult as it sounds. The procedure shown here is a systematic method for locating the lowest spot on a ceiling, then installing the furring strips.

You may need a good number of shims to complete the furring strip installation, but you can easily make them at home from scraps of plywood and hardboard. The amount of time you'll spend on this project depends on the condition of the existing ceiling. For a room that measures 10x12 feet, you and your helper should allow 4-6 hours to check the ceiling and install the furring. Before you begin, clear the room, and mark the location of all ceiling joists.

Editor's Tip: A drywall ceiling suspension system is somewhat like the familiar dropped ceiling that accepts tiles, but the members are engineered for face-application of drywall—up to doubled 5/8-inch panels. You'll lose a few inches of ceiling height, but the metal system installs fast and produces flat framing for great results.

More Ways to Amp up Your Ceiling

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What You Need

  • Stud finder
  • Hammer
  • Ladders
  • Two chalk lines with different colors of chalk
  • Mason's line
  • Level
  • Line level
  • Shims
  • Furring strips
  • Nails
  • Screws for installing strips

Step 1: Find Joists

Use a stud finder to locate the joists, then snap chalk lines to indicate the centerline of each one. Using a different color chalk, mark the centerlines of the furring strips, typically 16 inches on center.

Step 2: Cut Furring Strips

Cut two 1x3 furring strips about 1 inch shorter than the two ends of the room that are at right angles to the joists. Tack the first strip to one wall, leveling it with the top edge about 3/4 inch below the ceiling.

Step 3: Mark and Install Strips

Using a mason's line and a line level, transfer the bottom edge of the first furring strip to the opposite wall. Mark the second wall, and install the second furring strip level to the first one.

Step 4: Check with String

String a nylon mason's line between the first top nails on the two strips. Hold a scrap piece of strip next to the string at the furring strip centerline marked on the ceiling. If the string is below the furring strip, ignore it for now. If the strip projects past the string, measure the amount, and write it on the ceiling. Move the string 12 inches, and repeat the process until you've checked the entire ceiling surface. The largest measurement indicates the lowest part of the ceiling. If there are several spots with an identical measurement, you can start at any one of them.

Step 5: Remove Temporary Strips

Screw a furring strip flush against the ceiling at the low point, and shim its ends to level it. Now you have a level surface across the room. Remove the temporary strips at the ends of the room.

Step 6: Snap Lines from First Strip

Clip a line level onto a mason's line and run it from the bottom center of the first furring strip to the corners of the room, making pencil marks. Snap chalk lines on the walls connecting the corners.

Step 7: Install More Strips

Install each furring strip by first shimming its ends flush with the chalk lines on the walls. Using a level or straightedge along the bottom of the strip, secure its midpoint. At the remaining attachment points, gently slide in the shims so that you don't bow the strip, then nail through the shims into the joists. Work carefully, checking that each new strip you install is straight and level with the previous one.

How to Make Shims

For this project, flat shims work great to fill most of the space. Make your own by ripping 2-inch wide strips of 1/8-inch hardboard and plywood that's 1/4- and 1/2-inch thick. Crosscut the strips into 4-inch lengths with your miter saw. By combining these three thicknesses, you'll quickly fill the openings between the furring strips and ceiling. For fussy final adjustments or leveling, use tapered shims in pairs—install one from each side of the strip—so that you don't twist the wood.

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