In almost every way, the modern drywall-over-studs wall is better than its timber-and-masonry and plaster-and- lath ancestors. It’s fast and easy to build, lightweight and makes the most of inexpensive materials. But when it comes to stopping sound, the modern wall is a flop.
This article will show you how to make these walls (and ceilings) block sound better. The process involves ripping the existing drywall off the walls (and perhaps the ceiling), filling the walls with fiberglass insulation, attaching metal strips called “resilient channel” to the studs, and fastening new drywall to the channel.
This straightforward project doesn’t require specialized tools or high-level construction skills. Anyone who has experience hanging and taping drywall, along with a little carpentry and electrical know-how, can do this job.
Soundproofing is a messy, labor-intensive project, however. To minimize household havoc, it’s best to focus on one room, or at least one room at a time. The room might be a place that you want to keep sound out of—a home office, for example. Or it may be a room you want to keep sound in—like a home theater.
We won’t show you how to block noise coming from outside since most exterior walls already block sound fairly well. And any improvement you make to them will be of marginal benefit unless you also upgrade your windows.
Resilient channel acts as a spring between the drywall and studs. When sound waves strike a wall built with resilient channel, the drywall can vibrate independently without transferring the vibration to the studs. The metal channel is available at some home centers and all drywall suppliers.
- Fiberglass insulation batts are available at home centers. Although “acoustic batts” are available, plain old unfaced R-11 thermal insulation works just as well. Don’t spend more for R-13 batts; a higher R-value may actually cut the STC rating slightly.
- Type X 5/8-in. drywall is available at lumberyards and home centers. Type X drywall is meant for fire-resistance, but since it’s denser than standard drywall, it also stops sound better, especially when used with resilient channel.
- Acoustical sealant is available at drywall suppliers, but silicone caulk found at home centers is also a good choice. With either type, you’ll need lots of it and will probably save a few bucks by buying a big caulking gun that uses the more economical 30-oz. tubes.
- For attaching the channel to studs, use 1-1/4 in. screws. For attaching drywall to channel, use 1-in. screws. Fine-threaded screws grab on to resilient channel better than the coarse-threaded versions.
- Door gaskets, door sweeps and transition strips are available at home centers.
Before you tackle this project
Figure A: Sound Control vs. Ventilation
By making a room airtight, you’ll certainly make it more soundproof. But unless your home has a forced-air heating/cooling system, you may also create an air-quality problem. An unventilated room may simply become stuffy. But in some cases, it could become unhealthful, especially for those with asthma or chemical sensitivities.
One way to ventilate a room and still limit sound travel is to install a short section of duct in an interior wall. By making the duct from fiberglass duct board and offsetting the grilles, you create a “sound trap” that allows air to pass between rooms.
The sound-stopping methods covered in this article have proved themselves over decades of laboratory testing and real-world use. But they’re the sound-control equivalent of major surgery, and you should consider two other options before you go ahead:
1. Deal with the source of the sound.
Listen to the noises you want to block out. If footsteps on the floor above you sound like hammer blows, consider carpet instead of notoriously noisy coverings like wood or tile. Think about replacing old groaning appliances. Does the TV or stereo really have to be so loud or do you turn it up just out of habit? Limiting noise at the source is sometimes cheap and easy (moving tuba practice into the basement), sometimes troublesome and expensive (replacing the dishwasher). But it’s the least complicated and most effective approach.
2. Make rooms as airtight as possible.
Like air, sound passes through the smallest cracks and holes. Think of the way sound comes past a door that’s cracked open just a fraction of an inch: Close the door, and the sound is noticeably quieter. All the tiny, often invisible pathways through a typical wall or floor add up to a gap larger than the one along that cracked-open door. Electrical boxes are major offenders. Remove outlets, switches and fixtures from their boxes (turn off the power first), and seal the holes inside the boxes with silicone caulk. Also caulk the gaps between the boxes and drywall. Add gaskets and sweeps to doors (Photos 9 through 11). You might even remove base boards to seal the gap between the drywall and the floor (Photo 8). We strongly recommend trying this approach before tearing up your walls. It’s low-cost, low-hassle and effective—and if you don’t get the results you want, you haven’t wasted much time or money.
Photo 1: The first step
Move electrical boxes that share the same stud cavity so that they’re separated by at least one stud. To allow for the 1/2-in. resilient channel and 5/8-in. drywall you’ll use later, mount boxes so that the outer edge of the box is 1-1/8 in. from the stud. Boxes that don’t need to be moved can be repositioned so they protrude 1-1/8 in. Or you can use box extenders. Always turn off the power at the main panel before working on electrical systems.
Photo 3: Insulate the walls
Fill stud cavities with R-11 fiberglass batts. The insulation should completely fill each cavity without open gaps or pockets. “Split” the insulation to fit around pipes or electrical cable. Cut the insulation with a utility knife so it fits squarely around electrical boxes. Wear gloves, a dust mask and eye protection when working with fiberglass.
Photo 4: Screw on backer strips
Screw or nail strips of 1/2-in. plywood to wall framing around doors and along the floor. The plywood simply provides a solid backing for nailing on door casing and baseboard later on. Resilient channel is springy and holds nails poorly. Don’t forget to stuff insulation into the gaps around door jambs.
“Sound transmission class” ratings indicate a wall’s (or floor’s) ability to block sound. STC ratings are determined in a laboratory under ideal conditions. There are all kinds of variables in the real world that STC ratings don’t take into account. (These include walls that contain plumbing lines and sound traveling around walls, through ducts and via other pathways.) Still, STC ratings are useful for comparing sound control methods and materials.
A typical wall made from 2x4 studs and covered with 1/2-in. drywall on both sides carries an STC rating of 34. You’d be able to hear, and partially understand, a loud conversation taking place on the other side of this standard wall. Put fiberglass insulation in this wall and its rating rises to 39. You’d still hear the voices on the other side, but they’d be muffled and unintelligible. Cover one side of the insulated wall with resilient channel and 5/8-in. drywall and the STC jumps to about 50. At this point you wouldn’t hear the conversation at all—unless they started shouting.
We chose this last wall combination (insulation, resilient channel, 5/8-in. drywall) as a good compromise between cost and effectiveness. But you can go further. For example, by attaching resilient channel to one side of the insulated wall and screwing on four layers of 1/2-in. drywall (two on both sides), you’ll get an STC of about 56.
Add Soundproofing to a Wall Without Demolishing It
Cut holes at the top of each stud cavity and blow cellulose insulation into the cavities. Cut new 5/8-in. drywall so it’s 1/4 in. short of the floor and ceiling. Then attach the new drywall sheets using special acoustical dampening adhesive and drywall screws. Caulk the gaps with acoustical caulk.
Alternative Attachment: “Whisper Clips” and “Headrails”
“Whisper Clips” and “headrails” (a metal firring strip similar to resilient channel) are an alternative to resilient channel with screws. Attach the whisper clips in a staggered fashion to the studs and clip on the headrails. Attach 5/8-in. drywall to the rails, leaving a 1/4-in. gap along the top and bottom. Fill the gaps with acoustical caulk. For extra soundproofing, add a second layer of drywall, staggering the seams.
Photo 7: Attach drywall
Screw drywall to the channel’s flange with the drywall sheets running vertical. On ceilings, too, the sheets must run perpendicular to the channel. Use 1-1/4 in. fine-thread drywall screws spaced no more than 12 in. apart. Important: Screw into the channel, not into the studs. Mark the stud locations on the floor and ceiling so you can avoid them.
Photo 8: Seal the edges
Fill the gap between the floor and drywall with acoustical sealant or silicone caulk. Seal cracks at the corners where walls meet other walls or the ceiling, but scrape away the excess sealant with a putty knife so you can finish these corners with joint compound as you normally would. Also seal around electrical boxes.
Photo 9: Seal doors with gaskets
Seal doors by applying adhesive-backed gaskets to the stop moldings. This will make your door harder to close, and you may have to install an adjustable strike plate to compensate for the thickness of the gasket. You’ll also need “jamb extensions,” strips of wood that make the door jamb flush with the drywall.
Photo 11: Add a door sweep
Screw a sweep to the back of the door, low enough so that it seals against the transition strip. If you have no need for a transition strip, you can use an automatic door sweep, available through our affiliation with Amazon.com, which rises above the floor when the door opens and drops down when the door is closed.
The metal ducts of a forced-air heating/ cooling system are a noise fighter’s archenemy. They not only punch large holes in a room but also carry sound throughout a house. If there are metal ducts connected to the room you want quieted, listen to the sounds entering the room. If they’re primarily coming through the ducts, this insulation/resilient channel project won’t help, no matter how soundproof you make the walls. And unfortunately, there’s not much you can do about metal ducts, short of lining them with fiberglass or replacing them with fiberglass ducts (large, often impractical projects).
The best way to keep sound from passing through a floor or ceiling into the room above or below is to use insulation and resilient channel. Ripping drywall off a ceiling in a room where you’re stripping the walls anyway isn’t such a big deal. But if you want to keep sound from traveling through the floor of a room, you have to tear out the ceiling in the room below or buy an acoustical floor covering. The good thing about stripping a ceiling is that you can block off spaces between joists.
NOTE: If the sound coming through your ceiling is primarily “impact noise” (such as footsteps or toys slamming against the floor), the best fix is a heavy carpet and pad.
A typical wood-panel or hollowcore door has an STC rating of about 17. By sealing between the jamb and wall framing, and adding weatherstripping gaskets and a door sweep (Photos 9 through 11), you can raise the STC to 20; that’s an easy, noticeable improvement, but maybe not enough.
A sound barrier is only as good as its weakest point. So if you go to the trouble of building a 50-STC wall with a 20-STC door, most of the benefit will be lost through the door. Keep this in mind when you decide whether or not to add insulation and sound channel to a wall with a door.
To reach an STC rating higher than 20, you have to replace your door and jamb. A well-sealed solidcore wood door has an STC of about 28. “Acoustical” wood doors with STCs in the 30-to-50 range are also available. Most lumberyards stock or can order interior solid-core doors, but for acoustical doors, your best bet is a supplier that caters to commercial construction.
What to do, what not to do
Here are some rules of thumb for stopping sound:
- Caulk like crazy. Your goal is an airtight room. Caulk around electrical boxes, light fixtures, and plumbing and heating lines. Seal up even the smallest holes and cracks. Remember, if air can pass through, so can sound.
- If you have old plaster-and-lath walls, don’t remove them to add insulation and resilient channel. Plaster-and- lath walls are good sound-stoppers. To improve them, just seal cracks and gaps.
- Removing ceiling drywall gives you a great opportunity to add light fixtures. If you choose recessed lights, buy those rated “IC” so you can surround them with insulation. Other recessed fixtures must not come in contact with insulation.
- You must remove existing drywall before installing resilient channel. Don’t simply attach the channel over existing drywall.
- If you go to the trouble of tearing off drywall, don’t cheat yourself by using resilient channel or insulation alone. Use them together and you’ll gain up to 15 STC points. But use either one alone and you’ll gain only four or five.
- Don’t bother attaching resilient channel to both sides of a wall. One side does the job.
- Don’t use resilient channel on steel studs. Steel studs absorb vibration by themselves, so there’s no need to use sound channel. A steel-stud wall with insulation alone performs about the same as a wood-framed wall with insulation and resilient channel.