Soundproof Interior Doors: What to Know Before You Buy

Sound is often a problem within homes. If you're lucky enough not to have the sound of leaf blowers, mowers, and traffic migrating to the inside of your home, you may have intra-house sound issues. Music or videos from one room may bother people in neighboring rooms. Conversation in the kitchen may disturb people trying to sleep. And even our household appliances—dishwashers, refrigerators, washers and dryers—can transmit throughout the house.

Various methods can be used to reduce sound transmission in interior spaces in your home. But one method of soundproofing that is often overlooked is also one of the simplest: buying the right kind of soundproof door. For many homeowners, replacing standard hollow-core interior passage doors with solid doors is the first step to a quieter house.

Basics of Sound Transmission in a House

The problem of sound within a house can be subjective and sometimes fraught with emotions. To measure the issue objectively, you need benchmarks.

Sound Transmission Class (STC) ratings assign a measure of the acoustical performance of a door, wall, or other household material. Higher STC values indicate a better ability to resist the transmission of sound. 

Common STC ratings:

• STC 25: Normal speech can be clearly understood

• STC 30: Loud speech can be understood; normal speech heard but not understood

• STC 35: Loud speech audible but not understandable

• STC 41: Loud speech sounds like just a murmur

• STC 45: Loud speech is barely audible

• STC 50: Loud musical instruments barely heard

STC Ratings For Doors and Walls

If interior walls are a weak enough barrier against sound within a home, then any wall penetration only promotes sound transmission. Doors are a weak link, with hollow-core doors being the weakest type of interior door of all.

Why Doors Are an Important Soundproofing Factor

Sound transmission often occurs because the drywall on walls and ceilings is too thin. But interior doors comprise a far greater amount of the wall space than you might first think. 

If the wall adjoining a noisy area comprises 80 square feet, then the door represents close to 20-percent of that area. The door itself often represents the weak spot in the wall when it comes to sound transmission, especially if it is a hollow-core door as is standard in most new home construction. 

As the STC numbers show, you can greatly improve the soundproofing of any wall simply by replacing a standard hollow-core door, which is usually filled with a cardboard honeycomb materials, with a solid wood slab door.

If you do nothing else, replacing the door alone will greatly reduce sound transmission from one room to the other. If you go further by adding a double layer of drywall on both sides of an insulated shared wall, plus adding soft materials such as wall-to-wall carpeting, runners, or area rugs, you can eliminate most of the sound.

Soundproof Interior Doors to Buy

• Solid-core textured six-panel door: More than any other door, this type of door will seamlessly replace your old six-panel hollow-core doors while giving you an STC rating of between 27 and 30. The look is identical to the old door but the performance will be greatly improved.

• Sliding solid wood barn door: Because this barn-style door slides on a track mounted above the door frame, it can be thicker and thus more soundproof than a door mounted within the doorframe.

• Solid composite interior door: Wood composite is a slurry of wood fiber and polyurethane resins that can closely mimic the look of real wood and which provides excellent insulation against both sound.

Door Replacement as a Means of Soundproofing

Door replacement is usually a fairly easy matter since the factory stock doors found in most home construction use standard dimensions and often have the same positions for hinges and lockset. In many cases, it can be as simple as removing the old door from the hinges and putting the new solid-core door onto the same hinge plate already attached to the door jamb.

Be aware that solid doors are considerably heavier than hollow-core doors, and you may need to reinforce the hinges with longer, sturdier screws to support the weight.

If you cannot find a solid wood door of exactly the same dimensions or with the same hinge and lockset placements, you may then have to cut new hinge and strike-plate mortises into the door jambs. Some trimming of the door will be necessary to fit an odd-sized door opening, as is sometimes the case in older homes. This can take some precision work and might be a job for a professional craftsman who is familiar with such work. 

Because custom-trimming a replacement door to fit can be an exasperating task, some homeowners choose to remove all of the door trim, plus the entire door and frame down to the studs, before installing a new prehung solid-core door.

Prehung doors come already installed on hinges and fitted into a frame. Installation requires sliding the door-and-frame unit into the rough opening, shimming and nailing it in place, then replacing the door trim moldings.