Building A Sound Wall
A Quiet Home is a Sanctuary.
What constitutes a good building envelope? Three main categories include keeping the conditioned air where we want it (inside), controlling moisture and vapor, and keeping outside pollutants out. These pollutants include not only airborne particles like pollen in the summer, smog during air-stagnation, and smoke during the wildfire season, but also sound pollution. A quiet and calm interior can make a big difference to the well-being of the inhabitants of a home.
What strategies can we use to minimize sound from the outside getting in, or sound interference between zones in the house? Like the concept of heat transfer, acoustic transmission through materials depends on their ability to conduct or dampen sound. In a standard 2x6 exterior wall, for example, batt insulation can do a good job at dampening sound, but this effect can be negated by the studs that provide a solid bridge between the wall’s exterior sheathing and finishes to interior drywall.
If a truck rumbles down the street, sound can reach the inside in two main ways. The first is through airborne sound waves that contact the exterior walls, and the second is from a vibrating foundation. In our passive panel, we mitigate the first effect by isolating the interior conditioned surfaces as much as possible from the exterior by utilizing our 24” on center spaced double stud system. Its continuous insulated gap between the two stud bays provides an elastic space to dampen acoustic transmission between outside and inside. Our excellent air sealing ensures that sound waves, which travel through even the smallest air gaps easily, are prevented from doing so. Coupling our wall with higher performance windows that often come with triple paned glass is also a great way to attenuate unwanted sound. The second mode of vibrations conducted by the foundation are harder to dampen but can be limited with acoustic sealant under the sill plates, as well as insulation between the first floor’s joists.
How about sound transmission between rooms inside the house? A regular 2x4 wall with no sound isolating strategies implemented has a Sound Transmission Class (STC) rating of 33, which means that speech on one side can be heard on the other. One of the easiest ways to deal with this is to use batt insulation like regular cellulose and fiberglass, which can up this rating to around 39, where loud talking may be heard but would be hard to understand. Using more premium products like cellulose-based acoustical panels (a low-carbon option) or Rockwool Safe‘n’Sound (which has the additional benefit of fireproofing) in the interior stud and floor joist bays can greatly improve the STC to 45 or 50, where loud noises are very faint. Leveling up from sound dampening to soundproofing requires upgrading and doubling up drywall with a product like QuietRock in combination with an acoustic sealant on the edges and choosing solid core doors in addition to the previous strategies. At this level of sound deadening, no one can interrupt your afternoon nap!