What Thickness of Gypsum for Ceiling & Walls?

After World War II, the traditional way of constructing interior walls by smoothing plaster over wood laths gave way to the installation of compressed gypsum panels. Gypsum wallboard, also called drywall, is much quicker to install than plaster and the finished effect is a smoother wall. Local building code will require a minimum thickness, or type, of gypsum wallboard in some situations. When it's not regulated, industry standards will help you determine the best panel thickness for your project.

Hanging 1/2-inch gypsum wallboard is standard for finishing a ceiling with joists on 16-inch centers. This means that from the center of one joist to the center of the next, it is exactly 16 inches. Thinner wallboard, such as 1/4-inch or 3/8-inch, usually isn't sturdy enough for a wave-free ceiling. If you're hanging the wallboard on a ceiling with wider, 24-inch centers, upgrade to 5/8-inch gypsum.

The thickness of the wall between one room and the next depends on the thickness of the wallboard. A standard interior wall, framed with 2-by-4 studs and covered on each side with 1/2-inch-thick wallboard, is a total of 4 1/2 inches thick. When you're determining how thick you want the finished wall, keep in mind that dimensional lumber is 1/2 inch less than the dimension given. So, a 2-by-4 is really 1 1/2 inches by 3 1/2 inches. The same rule for wallboard thickness on a ceiling also holds true on walls. Minimum thickness of 1/2 inch is suitable for wall studs on 16-inch centers, but use 5/8-inch wallboard for 24-inch centers.

You may use thinner gypsum on walls and ceilings, but these panels serve different purposes. Both 1/4-inch and 3/8-inch wallboards are instrumental in covering curved walls, because they're thin enough to bend slightly, allowing the carpenter to coax the panels around a spiral staircase or onto a barrel ceiling. For rounded gypsum applications, two layers of thin drywall, installed one at a time, are standard. Thin wallboard is also beneficial as an overlay on an existing wall or ceiling. In cases where a wall has many dings or stains, or the homeowner tried unsuccessfully to strip off old wallpaper, a layer of thin gypsum creates a new-looking wall.

Builders install thicker wallboard on walls and ceilings that separate individual residences or commercial stores. Called "party walls" because separate parties occupy the opposing spaces, gypsum wallboard must conform to local or state fire codes to reduce the risk of fire spreading from one space to the next. Party wall codes vary, but you might have to install two, 1/2-inch-thick layers of gypsum wallboard with staggered joints. Alternately, you might have to install special fire-rated wallboard.