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Acoustical material is designed to meet a variety of standard federal ratings. Manufacturers generally rate the Sound Transmission Class (STC) and the Noise Reduction Coefficient (NRC) of their products. (See Acoustics.) While increasing the thickness of the material will often increase the NRC or STC, the most important factors in these ratings are the surface finish and composition of the material. Acoustical products are also rated for their fire resistance, surface burning and light-reflection characteristics.

Acoustical Material

Acoustical material is made primarily from mineral, fiberglass, vinyl or wood. Presently, a new generation of acoustical material, called Orion, is being introduced to replace fiberglass. In the past, asbestos cement was common because it's noncombustible and resistant to high moisture conditions. However, it's rarely used anymore because of the concern for asbestos-related health problems. (See Asbestos.) Cellulose fiber, the oldest and cheapest acoustical material, is also seldom used anymore. It's not fire rated, and it doesn't hold up well when subjected to moisture.

Mineral Fiber

Mineral fiber is by far the most common acoustical material. It's made from mineral wool — blast-furnace slag that's been reheated and blown into wool or spun into filaments. The process produces a highly durable, fire-rated material. Then the surface is either fissured or perforated to absorb sound. Where appearance is important, the material has fissures (voids) in the surface. It's perforated (with regular holes) more often in industrial settings where maximum performance is more important than appearance. As a general rule of thumb, the rougher the texture, the better the material will absorb sound. When you paint mineral fiber material, it's extremely important to use a nonbridging paint. Otherwise, the paint may close the pores, destroying the material's acoustical qualities.

Because there are so many kinds of mineral fiber acoustical materials, they fall within a wide NRC range, from the 0.40s to the 0.80s. The STC range generally falls between 35 and 49.

Fiberglass

Glass fiber, or fiberglass, is made up of tiny glass rods less than 1/20 the diameter of a human hair. These rods are pressed together, creating tiny voids between the fibers. These voids absorb the sound. Glass fiber tends to fall into a high NRC range, but it has a low STC. A backing such as foil can be used to improve the STC. A further disadvantage of glass fiber is that it doesn't come in a fire-rated form, more because it can't meet the weight standards (1 pound per square foot) than because the material is combustible. Fiberglass is more expensive than mineral fiber. Also, there's growing concern that fiberglass may be a health hazard, so its use is decreasing.

Vinyl

Vinyl-covered gypsum is occasionally used in food processing areas or garages because it's easy to clean. The smooth surface of the vinyl keeps it from absorbing sound, so the product has a low or unrated NRC. But the STC range is very good.

Wood Fiber

Wood fiber, or fiberboard, is a lightweight backing that comes in 4 × 8-foot sheets, 1/2 inch thick. Fiberboard is often used instead of gypsum board if acoustic performance is a consideration. Fiberboard with an acoustical coating has a good NRC rating. You can't use it for ceilings in commercial applications, but you can use it for walls.

Orion

Orion is a unique acoustical material. The material, an oatmeal-like substance, is dumped into 8-foot wide pans and shaken and shifted until it settles into flat sheets. Rollers squeeze out the excess water. The material is kiln dried for 8 to 10 hours and then cut to size. Orion is presently more expensive than other common acoustical materials, but its high NRC (up to 1.00) makes it an attractive option.

Acoustical Characteristics

Fire Resistance

Fire resistance measures how well a structure keeps fire from spreading from one part of a building to another, while maintaining structural integrity. In the past, material was classed A, B, C, or D. Currently, material is either Class A (nonfire-rated), or fire rated into 1, 2, or 3 hour classes. Fire-rated material has ceramic in it to slow its burning. Class A material may be used only in residential construction.

Fire-resistance ratings are frequently misunderstood by architects and builders alike. They often assume that by using 1-hour panels, they have a 1-hour ceiling. But classifications are established for an entire system and not just one component in the design. For instance, while 3-hour material will be slower-burning than 1-hour material, it will still burn through in less than 3 hours. The larger design of which it's a part, however, will theoretically keep a fire from spreading for 3 hours. The fire-resistance capabilities of a system are tested according to Underwriters Laboratories' specifications. If, during a fire test, a panel stays in its grid from 60-119 minutes, it's considered 1-hour rated. From 120-179 minutes, it's 2 hour. And from 180-223 minutes, it's considered 3 hour.

Surface Burning Characteristics

Surface burning characteristics are measured by observing how quickly flames spread and how much smoke develops. These factors are then expressed in a single number. The number is relative to how red oak burns (100) and inorganic reinforced cement board burns (0). Acoustical material commonly falls into the 0-25 range.

Light Reflection

Material is classified into light reflection (LR) grades, with 1.0 reflecting the most light. A grade of LR 1 means 75 to 100 percent of the light is reflected back; LR 2 is 70 to 74 percent reflection; LR 3 is 65 to 69 percent; LR 4 is 60 to 64 percent. Under 60 percent is ungraded. The vast majority of acoustical material falls into the first two grades, with LR 1 being the most common.

In addition to these federal ratings, you have to consider other characteristics for acoustical material. You'll weigh the ease of installation and maintenance, resistance to moisture, insulating properties, and cost as well.

Installing Acoustical Ceiling Tiles

There are two common ways to install acoustical ceiling tiles: directly to a smooth backing or attached to furring strips (Figure 1), or suspended in a metal grid (Figure 2). For either method, schedule ahead so the materials are delivered at least 24 hours before installation. Store them in the location they'll be used. That way, any shrinking or swelling due to temperature or humidity will happen before you install it.

Although it's not particularly difficult to hang a suspended ceiling, you can hire a drywall sub if you don't want to do it yourself.

Layout

Your finished ceiling will look better if the border tiles are the same width and none of them are less than half a tile wide. For instance, if you're using 12-inch tiles, you wouldn't want to have a row of full tiles on one end and a row of 4-inch tiles on the opposite end. For better balance, plan a row of 8-inch tiles on each end (12" + 4" ÷ 2 = 8"). To make sure this happens, you'll need to do a little simple preplanning. First measure the length and width of the room. Then snap a chalk line the length, width, and both diagonals of the room to find the center point. Finally, use Figure 3 to position the ceiling tile.

Cut the tile, face up, with a utility knife and a straightedge. Or score the face with a utility knife, and then follow with a handsaw or power saw with the face side still up.

Installing Ceiling Tiles

Ceiling tiles come in a variety of sizes. The 12- × 12-inch square tiles are the most common, but 12- × 24-inch tiles are also frequently used. Figure 4 shows a tongue-and-groove ceiling tile.

If the ceiling is level and in good shape, you can glue the tiles directly to the surface. But first allow new concrete to cure at least six months and new plaster to cure at least a month. Don't glue tile directly to concrete unless you've insulated and vented properly and placed a vapor barrier to avoid temperature and humidity differences. (See Insulation.) Prime the surface of new concrete, and clean all dust from the surfaces where you'll apply adhesive.

If the ceiling is in poor shape, install 1 × 3 furring strips 12 inches on center at right angles to the ceiling joists. Work from the center of the room out, shimming the furring strips wherever needed to make a level surface.

Furring Strip Method

Snap a chalk line for each border. Make sure the chalk line is parallel to the center line, not the wall. Cut corner tile to size, cutting off the two tongue sides. Cut the tongue side off of all border tiles for the first horizontal and vertical rows, adjusting for any unevenness in the walls. See Figure 5.

Place the first tile in the corner, flange side out. Nail the flush sides of the tile at the corner and walls. Continue with the border tiles, nailing the side against the wall and stapling the flanges to the furring strips. Putty the nail holes when the tiles are all in place.

Build out from the corner, slipping the tongue into the border tiles' grooves. Staple the flanges to the furring strips. For 12 × 12-inch tiles, use three staples to a side. Use five staples to a side for 12 × 24-inch tiles. Work across the room diagonally. See Figure 6.

Tools and Materials

Utility knife

Level or straightedge

Chalk line

Talcum powder or corn starch (use on your hands before handling tile to keep from smudging it)

Staple gun with 9/16 inch staples or

Hammer and 4d nails or

Tile adhesive, brush, and putty knife; mineral spirits

Putty

Goggles

Dust mask

Protective clothing

Solid Backing Method

Follow steps just described for layout, cutting, and placement of tile.

Brush a light coat of glue on the back of the tile. Dab a walnutsize ball of glue on each corner about 2 inches in. (For 12 x 24- inch tiles, place eight balls of glue.) Press the tile firmly in place, sliding it into the adjacent tongue and groove, or kerf. Then clean up the adhesive with mineral spirits.

If the wall is solid drywall in good condition, you can staple the tiles directly to it in the pattern described.

Estimating Acoustical Ceiling Tiles

Estimate how many tiles you'll need by calculating the square footage of the ceiling (length times width). For 12- × 12-inch tiles, the square footage is the same as the number of tiles you need. If you're using 12- × 24-inch tiles, divide the square footage by 2.

A two-person crew installing 12- × 12-inch tongue-and-groove ceiling tile with staples should be able to install about 58 tiles an hour. This will, of course, vary with the layout of the room. You can set more tiles per hour in a large open room, and substantially fewer per hour in small or cut-up rooms. If you use furring strips, a carpenter and a laborer should be able to install around 40 square feet of 1 × 2s at 12 inches on center per hour.

Repairing Ceiling Tiles

Use a utility knife to cut out damaged tile, scraping out stubborn pieces and adhesive with a putty knife. Clean out the grooves.

Cut a new tile to fit, removing its tongues and flanges. Glue or nail it in place.

Installing a Suspended Ceiling

When a ceiling needs to be lowered or you need easy access to wiring, ductwork and pipes, a suspended ceiling is a better choice than ceiling tile. The most common sizes used in suspended ceilings are 24 × 24 inches and 24 x 48 inches. The tiles are laid in a metal grid that's suspended from the ceiling. Allow at least 2 to 3 inches between the ceiling or joists and the new ceiling. It will be difficult to maneuver tiles into place if there's less space than that. Look at Figure 7

Don't hang light fixtures or other ceiling apparatus from the metal grid unless you're sure the system can support their weight. It's better to suspend the fixtures directly from the ceiling.

By far the most difficult part of hanging a suspended ceiling is getting it level. If the ceiling isn't perfectly flat, the tiles will rock or tip or appear out of line. Professional ceiling installers use laser levels to do the job right. For someone who only does an occasional ceiling, sighting in with a transit will work. If you don't have a transit, check repeatedly with your level and tape measure while hanging the wall angles and the main tees. See Figure 8. For small areas, you can get by with leveling with a builder's level (Figure 9).

Estimate the number of panels by finding the square footage of the ceiling, then dividing by 4 (for 2- × 2-foot panels) or 8 (for 2- × 4- foot panels). Or sketch the ceiling on paper and count the number of panels.

Installation Guidelines

Snap a chalk line around the room at the height where the new ceiling should go. Fasten the wall angle at this line. Cut your pieces carefully to make sure every end is fastened to a stud. Use nails, screws, or staples to attach the pieces to the studs. Use concrete nails to attach pieces to masonry. Miter outside corners; butt inside ones.

Snap a chalk line on the ceiling or ceiling joist to mark the center main tee. Hammer in 6d nails above the wall angles on both sides of the room where cross tees go. Tightly stretch the string across the room and tie it to the nails.

Cut suspension wires for the main tees. Attach screw eyes or hooks and nails to the ceiling joists at the chalk line every 4 feet where the cross tees will run. Slots in the main tee for the cross tees must line up with the cross strings.

Insert suspension wires through the screw eyes, twisting excess wire around itself. Insert the other end through the main tee and secure the loose wire by twisting it around itself. Make sure the tee is level. If the length of the room is more than 12 feet, splice two main tees together with a splice plate. Wire both sides of the splice. See Figure 10.

When main tees are in place, connect in the cross tees (Figure 11). Check again to make sure the entire system is level. Set in the panels by angling them up through the space, straightening the panel, and laying it in place.

Materials and Equipment

Wall angle: L-shaped piece attached to the wall around the perimeter of the room; available in 10- or 12-foot lengths; nailed, screwed or stapled to the wall (see sidebar)

Main tee: T-shaped piece for spanning the length of the room; placed at right angles to the joists; available in 8- or 12-foot sections; hung from the ceiling with screw eyes and wire

Cross tee: T-shaped piece for spanning the width of the room, placed parallel with the joists; available in 2- or 4-foot sections; connects into the main tees by tabs and slots

Splice plate: Straight piece with slots, used to connect main tees

Screw eyes or hook and nail: Attached to the ceiling to hold wire; allow one for every 4 feet of main tee

Wire: 18-gauge hanger wire for hanging the main tees; cut at least 4 inches longer than the distance between the old and new ceilings

Tin snips: To cut steel tees and angles or

Hacksaw: To cut aluminum

Chalk line

Transit and/or level

Fasteners (staples, nails, or screws) with appropriate fastening equipment

6d nails

Hammer

String

Utility knife and/or saw (to cut panels)

Attaching Wall Angle to Drywall

When backing isn't convenient, here's a slick way to attach the wall angle to drywall. But remember that it's only as strong as the drywall and the staple. You can't use this technique structurally, but it will work to attach a wall angle to support acoustic tile.Use a heavy gauge fence staple and follow these steps:

With the metal angle molding in place, strike the staple, centering on only one of the points. For this technique to work,make sure only one of the points pierces the metal.

Strike the outer corner of the staple to continue to drive it sideways through the metal and the drywall. Carefully direct the force of the hammer on the staple, so you're driving only one point into the metal.

When the staple is tight, it will secure the metal anchor by pinching it to the drywall.

Estimating a Suspended Ceiling

Estimate how many tiles you'll need by calculating the square footage of the ceiling (length times width). If you're using 12 × 24-inch tiles, divide the square footage by 2.

A two-person crew can usually install about 100 square feet of standard 2 × 4-foot grid with wires per hour. Be sure to allow additional time for cut-up or small rooms.

Placing the ceiling tile in the grid is a simple drop-in process except for borders, corners, lighting, columns and other nuisances. For a simple drop-in ceiling using an average price nonrated tile, the two person crew should be able to install around 250 square feet, or 32 tiles per hour. Tile prices vary depending on cut, style, texture and fire rating.

Manhours to Install Acoustical Ceiling, per SF

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Type Manhours Suggested

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Crew Ceiling tiles, 12" × 12"

glued or stapled .035 1 carpenter

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Suspended ceilings:

Grid system, 2' × 2' .017 1 carpenter

Grid system, 2' × 4' .015 1 carpenter

Add for under 400 SF job .007 1 carpenter

Ceiling tiles, deep textured,

3/4" reveal edge .010 1 carpenter

Ceiling tiles, random pinhole

or fissured, 5/8" square edge .004 1 carpenter

Manhours

For information on related topics, see:

Acoustics, page 21

Asbestos, page 31

Insulation, page 395