Basement Soundproofing

 

 There are a variety of reasons for soundproofing your basement. Many times a home owner wants to renovate the basement so they can rent it out to potential tenants. Sometimes they just want to build a recreation area in the basement with perhaps a home theater and other entertainment facility and they want to keep the noise in the basement and not have it travel up the floors above.

 Whatever the reason is that you would like to soundproof your basement, here are some pointers and methods for keeping the sound from  transmitting between floors and for stopping the foot fall traffic above from being transmitted to the basement area.

 One of the major problems you will come across when dealing with a basement soundproofing project is low floor to ceiling heights. Sometimes this precludes you from floating the ceiling on Sound Clips and furring channels,  If you have typical 8’ or higher ceilings in your basement, then all of the soundproofing options are open to you. Many times when building out a basement people want to install recessed lighting in the ceiling. I generally discourage people from using recessed lighting in a ceiling because they are a serious breach in the soundproofing effort. That being said, that are a multitude of ways to soundproof the canned lights and  still maintain the acoustical properties of the ceiling assembly. We will discuss  soundproofing recessed lighting in a subsequent post.

The ceiling is where you want to start when soundproofing a basement. You can either do your soundproofing from below or put down a soundproof floor underlayment above and soundproof your upper floor at the source. The recycled rubber floor underlayments that we carry at Soundproofing America, Inc would be perfect in this application.

 Let’s get to work on the basement ceiling. I am assuming that there is no drywall on the basement ceiling so we will be working with bare joists and studs on the walls and ceiling. In the  joist cavity of your ceiling assembly it is recommended that you add a sound absorbing insulation that will friction fit in the cavity and will be positioned right up against the sub floor above Some Great insulations are Rockwool (Roxul safe and Sound or Roxul AFB are both good choices) You also have the option of using the recycled bonded cotton called (Ultra Touch), Either one of these product will offer great sound absorption in the joist and wall cavities. The joist cavities will be deeper than one layer of the R-19 sound insulation would fill. You would simply fill the rest of the cavity with  standard fiberglass insulation (the pink stuff will work).

 Once the cavities are filled with the sound absorbing insulations we will be stapling up a layer of the 1% per sq ft mass loaded vinyl. (MLV for short) MLV is a high grade vinyl that is impregnated with barium and silica to give it mass. It was designed to emulate lead sheeting. It has all of the characteristics of lead but it contains no lead whatsoever. MLV comes in rolls that are 4’ X 25’ long or 4.5’ X 30’ long. It is no picnic attaching this to a ceiling, but you can always cut the vinyl into more manageable lengths. You will still need at least 2 people to install the MLV to your ceiling. Using an air drive stapler or nail gun, you would staple the MLV directly to the face of the joists, overlapping the seams by about 1” and then caulking the over lap as well as the perimeter of the MLV membrane.

Now that you have the MLV attached to the ceiling and properly sealed with the acoustical caulk, you come to a crossroads. If you have 8’ or higher floor to  ceiling joists, then you can float a new ceiling using Sound Clips and metal furring channels. Sound clips are a device that is used to completely isolate a ceiling from the joist structure above. We will be talking about floating your ceiling is later posts. It takes a lot of time to explain the floated ceiling concept in one post.

The next option would be to add 2 layers of quality 5/8” drywall (good brands are National and US gypsum), You would basically screw up the first layer of drywall directly over the MLV membrane making sure to screw into the joist only. You only want to perforate the MLV where it is on the joist itself. Putting unnecessary punctures in the center of the membrane degrades the amount of soundproofing you will obtain. Once the first layer of drywall is up on the ceiling, I would recommend that you place the second layer of 5/8” drywall onto aw horses and apply a damping compound that we call Green Glue directly to the surface of the new drywall where it will mate with the first layer of drywall that is already installed on the ceiling. The Green Glue comes in 29oz caulk tubes. You would cut the tip for a ¼” bead and then shoot it out onto the drywall in an “S” pattern. The distance between the “S” would be about ½” apart. You will need to apply 2 full tubes of Green Glue for each 4’ X 8’ sheet of drywall. Leave the Green glue in the ¼” bead, do not trowel it out or spread it out. When you screw the new layer over top of the existing layer of drywall, the Green Glue will automatically spread out evenly. That is a characteristic of a visco elastic compound. In essence, the Green Glue will damp both layers of drywall and thus will remove the Drywall’s ability to transmit sound, It is not 100% effective but the Green Glue with 2 layers of drywall can add up to 35-38 STC points to any ceiling. Basically that equated to a 35-38 Decibel reduction of sound through the ceiling.

 Dealing with the walls is not as critical as the ceiling, but if you need to block noise from one room to another, it is recommended that you add the sound absorbing insulation to the open walls and perhaps installing  a layer of the MLV prior to installing the drywall.

I have pretty much described to you exactly what needs to be done to soundproof a basement. I could not get into doors and windows in the basement but we will cover those areas later. Thanks for reading and learning about soundproofing your basement. This is Dr. Bob, Adios!

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