Guide to gypsum board and drywall
Regular drywall panels are 48 inches wide and come in a variety of lengths, ranging from 8 to 16 feet. Panels are available in four thicknesses – ⅝ inch, ½ inch, ⅜ inch, and ¼ inch.
When most people think of gypsum board (also commonly called drywall), they probably picture the standard 4×8 panel that’s been in use since gypsum board first became popular.
But that is by no means the only size or type available. Today gypsum board comes in lengths of up to 16 feet and in 48- and 54-inch widths.
A wide variety of special-use gypsum board is also available, including moisture- and mold-resistant, fire-resistant, and impact or abuse-resistant panels; ¼-inch flexible panels; ½-inch high-strength ceiling panels; and foil-backed panels. A relatively new lightweight drywall is also available weighing as much as 30 percent less that standard ½-inch drywall.
This article will explain the various types of gypsum board and their uses, including thickness and lengths available, and framing specifications. Knowing what types and dimensions of drywall are available can make a big difference in the final performance and lasting quality of the installation.
Most types of drywall are available in lengths of up to 16 feet. The longer lengths are used to help eliminate or reduce the number of butted seams.
Gypsum board sizes
Regular drywall panels are 48 inches wide and come in a variety of lengths, ranging from 8 to 16 feet. Panels are available in four thicknesses – ⅝ inch, ½ inch, ⅜ inch, and ¼ inch – and each has specific application and framing requirements.
Most types of drywall are available in lengths of up to 16 feet. The longer lengths are used to help eliminate or reduce the number of butted seams. (A butted seam is created when the ends – un-tapered edges – of the panels are butted together.
The butted seam is necessary because the wall or ceiling is longer than the available length of drywall.) However, every drywall supplier is not going to stock the longer lengths or even some of the more specialized types of drywall, which means if you’re going to use one of these, you have to plan ahead and order enough material for the job.
54-inch-high gypsum board
One of the main goals when hanging drywall is to create as few seams as possible. That’s fine when hanging 4-foot-wide sheets on walls with 8-foot (or lower) ceilings, since the panels can be hung horizontally with just one seam running the length of the wall. But more and more homes are being constructed with 9-foot-high ceilings and 4-foot-wide drywall creates two horizontal seams on each wall.
To avoid the extra seam, use 54-inch-wide panels, which were introduced in the early 1990s for use on 9-foot-high ceilings; 54-inch drywall is available in regular drywall, moisture- and mold-resistant, and fire-resistant panels.
½-inch drywall, regular and lightweight
Half-inch regular drywall is probably the most commonly used drywall in new residential construction and remodeling (lightweight drywall is rapidly replacing this heavier product). It’s usually used as a single layer over wood or metal framing; however, it can be installed in two layers (with staggered seams) to increase fire resistance and sound control. If framing is farther apart than the recommended spacing, wood or metal furring strips can be attached across the framing to create the needed o.c. spacing.
Hanging drywall is hard work, in large part because it’s heavy. A sheet of regular ½-inch drywall weighs about 60 pounds. In contrast, the new lightweight ½-inch drywall weighs about 41 pounds.
A drywall hanger can hang 60 4×8 sheets a day, regular drywall at 60 pounds equals about 9 tons a week. If that can be reduced to 6 tons, productivity is increased and risk of injury is reduced. The lightweight ½-inch drywall is also a little tougher, a little stronger, and more resistant to sagging. The panels go into place easier and faster, and there’s less damage to the edges.
The lightweight panels utilize colloidal chemistry to create a significantly higher strength-to-weight ratio and improved sag resistance. The panels meet all International Building Code, International Residential Code and ASTM C1396 Specification for Gypsum Board, for both ½-inch gypsum wallboard and ½-inch gypsum ceiling board.
Because of the superior sag resistance, compared to regular ½-inch drywall, the panels are ideal for use on ceilings with up to 24-inch on-center framing and water-based texture, presenting potential cost-savings when used as a replacement for ⅝-inch type X board used on ceilings or ½-inch interior ceiling board.
Regular ½-inch drywall has always been approved for use on 24-inch spacing on ceilings but because there’s sometimes sagging heavy insulation, wet ceiling textures, or higher humidity, either a ½-inch ceiling board or ⅝-inch drywall are a better choice. Both are even heavier than regular drywall. Now a ½-inch thick lightweight product can be used throughout the job.
Lightweight drywall panels look the same as regular drywall. Paper face is the same. They’re cut and scored the same. The core is a little harder material so when cutting, the utility knife blade gets dull faster. There’s no difference when setting screws or sanding.
Even drywall supply yards like the lightweight drywall. It’s easier to handle at the yard and because of the lighter weight causes less wear and tear on trucks during delivery. It’s also easier for forklifts to handle, because it doesn’t sag as much.
Lightweight panels are available in standard lengths, including 8-, 10-, 12-, 14- and 16-foot panels in 48- and 54-inch widths. The ½-inch-thick panels are for use in non-fire-rated applications, such as residential construction, remodeling and repair projects. Note: Some drywall manufacturers are now making a lighter weight fire-resistant panel.
Regular ⅜-inch regular drywall
Regular ⅜-inch drywall panels were initially used to replace wood lathe as a backing for plaster. When drywall became popular, ⅜-inch panels were widely used on walls and ceilings in new construction, but it was eventually replaced by the more durable ½-inch product.
Today, ⅜-inch drywall is used mainly to cover existing surfaces in repair and remodeling work, or to provide a backing for paneling. It’s also used in double-layer applications.
Regular ¼-inch drywall
A lightweight panel commonly used to cover old walls in remodeling or to provide sound control in double-layer or multilayer applications, ¼-inch regular drywall panels are too weak to install in a single layer over bare studs or joists without a backing.
Regular ¼-inch drywall is easily bent and can be used to form curved surfaces with long radii (5 feet or more) if applied dry or shorter radii (3 feet or more) if applied wet. A better choice for curved surfaces, however, is ¼-inch flexible drywall.
Moisture- and mold-resistant drywall
Moisture- and mold-resistant drywall is an upgrade from traditional moisture-resistant drywall, but it’s not recommended for wet or high-moisture areas, such as a shower enclosure. Available in ½-inch regular or ⅝-inch fire-resistant panels, it’s used mainly as a wall covering over 16-inch o.c. framing.
When attached to a ceiling, use ⅝-inch panels over 16-inch centers and ½-inch panels over 12-inch (or less) centers. It’s most commonly found in 8- and 12-foot lengths.
Moisture- and mold-resistant drywall is available in specially treated paper faced panels and in paperless panels (Instead of being paper faced, the front and back is covered with a fiberglass mat. This inorganic material does not support mold growth.)
Moisture- and mold-resistant panels are not in themselves a vapor retarder. They feature moisture- and mold resistance, which they achieve through moisture- and mold-resistant face and back coverings, and a moisture- and mold-resistant gypsum core. There are other products that have a gypsum core that is a water-resistant barrier but moisture- and mold-resistant panels do not.
Fire-resistant gypsum board
Most regular gypsum board gets its naturally occurring fire resistance from the gypsum core. Gypsum board contains about 21 percent water. When it’s exposed to fire or heated, the water is slowly released as steam effectively retarding heat transmission. When the chemically combined water is released as steam, it acts as a thermal barrier until this slow process, known as calcination, is completed.
The temperature directly at the plane of calcination is only slightly higher than that of boiling water, which is significantly lower than the temperature at which steel begins loosing strength and wood ignites. Once calcination is complete, the gypsum continues to act as a barrier for the underlying structural members from direct exposure to flames.
However, in regular gypsum board shrinkage occurs because of the loss of water volume and cracks occur, which permits passage of fire and heat and can lead to the gypsum falling apart.
Fire-resistant drywall has special additives and non-combustible fibers in the core that help maintain the integrity of the gypsum core as water is lost, while providing greater resistance to heat transfer. Type X fire-resistant gypsum board must comply with ASTM C1396 and provide at least a two-hour fire resistance rating for ¾-inch board, one-hour fire rating for ⅝-inch, or a ¾-hour fire-resistance rating for ½-inch board.
Type C fire-resistant gypsum board has an improved formulation that exceeds ASTM requirements for Type X. Some brands have a core additive that expands when subjected to heat, which aids in holding the gypsum board together.
Many building codes specify fire-resistant gypsum board for attached garages, furnace or utility rooms, and ceilings and walls separating dwelling units in apartment and condominium complexes. The two most commonly used fire-resistant panels are ½ inch and ⅝-inch. Half-inch panels are convenient when you need to cover only part of a wall or ceiling with fire-resistant drywall and finish the rest with regular ½-inch panels.
TIP
Typically, only the first 5 feet of the ceiling adjacent to a house wall needs to be fire-resistant. Using matching thicknesses allows for a smooth transition at the joint. If different thicknesses were used (say, ⅝-inch fire-resistant and ½-inch regular), the seam would be difficult to hide during the taping process.
For fire resistance, ⅝-inch panels are the most commonly used. They have the one-hour fire rating that many building codes require. Since most garage-ceiling joists are 24-inch o.c., ⅝-inch panels work best because they are approved for 24-inch spacing.
Although manufacturers approve ½-inch panels for joists 24 inch o.c., they are more likely to sag, especially in a garage that is exposed to extremes in temperature and humidity. Because of the extra thickness and stronger core, ⅝-inch fire-resistant drywall stands up better to denting and other types of abuse than ½-inch drywall.
On the surface, these panels look the same as regular drywall, except for a stamp indicating that they are fire-resistant. The term fire resistance means the ability of a constructed assembly (a wall or a ceiling covered with drywall) to contain a fire.
–By Myron Ferguson, Ferguson Drywall Innovations, Middle Grove, New York
