Hearing the neighbors’ every move through walls or ceilings can be a make-or-break issue for residents. But given the multitude of soundproofing options available, developers and owners don't have to break the bank to keep the noise down.
The main metric for measuring soundproofing is called Sound Transmission Class (STC), and the higher the rating, the lower the noise. The required STC rating for shared walls in multifamily buildings is 50 if tested in a laboratory and 45 if tested in the field. Generally, at an STC rating of 40-50, loud speech is faintly heard, but at an STC rating above 50, loud noises are barely heard.
Soundproofing can be broken down into four basic elements: absorption, damping, decoupling, and mass. Usually, a solution that incorporates multiple areas is most effective. While mass is straightforward and can really only be affected by using more or thicker material, the other three components can be addressed in various ways.
Absorption can be easily improved by using insulation with a high sound-isolation value, which will provide benefits without requiring the use of additional materials such as wall panels or coatings. New England Soundproofing’s Quiet Insul is made of 80 percent recycled cotton fibers. The 5.5-inch thick Quiet Insul has an STC rating of 57, according to the company, while the 3.5-inch thick version lists an STC rating of 45. The application of a damping compound to construction barriers “deadens” the plane and reduces vibration. One solution is Green Glue Noiseproofing Compound, which is applied between two pieces of drywall to dissipate sound waves. According to the company, just one layer can eliminate up to 90 percent of noise, including low frequencies that are less impacted by other methods. Green Glue is certainly more cost-effective than purchasing factory-damped drywall, starting at around $0.50 a square foot.
Absorption and damping used in conjunction should deliver strong results, and at a low price point— since multifamily units already require a double layer of drywall, the added cost and installation for damping is minimal. However, luxury apartment developers looking to take soundproofing one step further can employ decoupling, in which walls are separated from the studs to disrupt sound’s path.
Resilient sound clips with a drywall furring channel, such as those offered by Acoustical Surfaces, are the best bet here. The RSIC-1 Resilient Sound Clip from Acoustical Surfaces can be used for both wood and steel framing in walls and ceilings. The company says that use of the RSIC-1 clips can add 20 STC points to walls. While decoupling is an extra step, the clips themselves are low-cost and easy to install.
When it comes to soundproofing floors, many of the same principles apply, but different elements may be used. Noise control mats applied over the subfloor are a popular option, as they are lightweight and easy to install. QT Sound Control’s QTscu is a floor underlayment made from recycled rubber that comes in five standard thicknesses, ranging from 2 mm to 15 mm. Depending on the thickness and the type of flooring used, the company reports STC ratings ranging from the high 50s to mid-60s. Acoustical soundboard is another cost-effective option for flooring applications. Homasote offers its 440 SoundBarrier wallboard, made of 100 percent cellulose fiber, which can be used for floors, walls, and ceilings. Three thicknesses are available, and the fiberboard is installed directly onto the subfloor. The product delivers an average STC rating of 53.
Ultimately, effective soundproofing is an investment that will pay dividends, as privacy and peace are highly valued qualities. If residents can’t hear their neighbors, chances are, building managers won’t hear complaints.
Laura McNulty is associate editor for Hanley Wood's residential construction group. Connect with her on Twitter @LMcNulty_HW.