Question: With space at a premium and land values at maximum, I'm building more and more two- or three-unit homes on one parcel of land -- often in inner city areas that have been renovated. These units are marketed to higher-end homeowners who demand privacy. How can I offer them that privacy from both the neighbors and sound that leaks in from the street?

Answer: It is becoming a common practice that with land values skyrocketing and the need for affordable housing at an all time high, that multi family units built on a single parcel of land are becoming quite the norm. Whenever you have shared walls, ceilings and floors, there will always be sound issues between units that are best addressed during the construction phase of the project. There are simple things that can be done during the building process to help reduce the transmission of sound from one unit to another. One effective method of sound isolation is to stagger the studs on the walls between units. Most builders know what staggered studs are, but for those that don’t, staggered studs are studs that are installed generally on a 6" footers where the studs are situated so as to be offset by a few inches so that every other stud contacts the drywall. The less contact the drywall has with the stud structure the less chance there is for structural sound transmission through the walls. This system also allows the drywall to resonate better and thus lets less sound will pass through. (A lot of science involved here) This is a pretty effective soundproofing method that only requires common building materials, but generally more serious measures will be needed if you want more complete soundproofing in each unit.

There is a wide array of soundproofing products available on the market today and especially over the Internet. At times all these materials can become overwhelming to the builders and developers. Some of the more common products for soundproofing are lead sheeting, mass loaded vinyl, bonded acoustical cotton insulation, mineral wool and rock wool as well as soundboard, green board and Homasote. Most builders are familiar with these products but are unsure on how to best install them.

There are conflicting reports throughout the industry as to what needs to be done inside stud and joist cavities for the best soundproofing. Many experts feel that if the dead air space is sealed properly it will add greatly to the soundproofing. I agree with this to a degree, but from our experience we have found that if you deaden the structure using a mineral wool or bonded cotton insulation, you’ll get much better results in combating structure borne noise transmission. Structural noise is always associated with impact or footfall (walking noise) and is the most difficult type of noise transmission to block.

There are sound batt insulation products such as Roxul AFB, Roxul SAFE and bonded acoustical cotton that can be used to fill stud and joist cavities. These materials will give you a good foundation for the “industrial strength" soundproofing materials such as mass loaded vinyl and lead sheeting that will be applied later down the line.

Once the cavities are filled, you are ready for some serious soundproofing. I will discuss mass loaded vinyl in this article, but there are other products that can be utilized as well.

Mass loaded vinyl (MLV for short), is a vinyl product that contains barium salts and silica that gives it the same soundproofing qualities as lead sheeting without the hazards and issues associated with lead. MLV is generally a class C building material and meets most building codes throughout the United States and Canada.

The MLV would be installed directly to the studs or the joist assembly using heavy-duty staples or roofing nails (nails with the large plastic heads). It will stretch across the studs for example, much like a drumhead or a membrane. We always recommend over lapping the seams wherever possible. Next you will caulk the seams (or overlap) as well as the entire perimeter of the MLV membrane with an acoustical caulk. Once the caulking is complete, we recommend taping the seams with an MLV sealer tape to maintain the blocking ability of the vinyl at it’s seams.

Now that you have your soundproof membrane system in place, you are ready to install the drywall. Generally we recommend installing 2 layers of ½" drywall directly atop of the MLV membrane, but if this is not in the budget, at least install one layer of 5/8" fire code drywall, then tape mud and paint as usual. A little hint; if you are indeed planning to install multiple layers of sheetrock, squeeze out a bead of the acoustical caulking between the two layers of drywall (use an “X" pattern and also caulk the perimeter of each sheet). This will add a small amount of dead air space and will minimize the drywall-to-drywall contact. This procedure should prove to be a very effective sound control system for any wall or ceiling in a multi family dwelling. When builders and developers take these extra steps, they will often costly avoid lawsuits or complaints from new owners or tenants. There are other methods of soundproofing that we will discuss in future articles. I hope this sheds some light on soundproofing products that can be installed during the construction phase of any multi family dwelling. These procedures can also be used for the construction or any single-family homes, as well as commercial and industrial spaces.

Dr.Bob is the Senior Technical Director for Soundproofing America, Inc in San Diego, California. Please feel free to contact him anytime from 8AM till 6PM PST. This is Dr. Bob....Out!!!



Bob Orther

Senior Technical Director

www.soundproofingamerica.com

Call toll free (877) 530-0139