Recent changes to the National Building Code have opened the door to taller wood-framed buildings, now up to a maximum of 6 stories. As a result, we are seeing more and more wood framed multi-unit residential projects breaking ground. This is great for the wood industry and sustainable building materials, but can produce a whole new set of acoustic challenges that architects, developers and designers have to grapple with. Wood framing allows sound to transfer through walls and ceilings very easily, creating a lot of potential noise issues if the design and acoustic details are not properly addressed.
The article will be the first of many on acoustics, and we’re going to focus on the basics of acoustics and strategies that can be used to help with sound issues in wood framed multi-unit construction. When talking about sound transfer, we are generally concerned with two different types of sound: airborne noise and impact noise. The distinction is important, because strategies that effectively address airborne noise may not work well for impact noise, and vice versa. In the building code and in project plans, you’ll often see metrics such as, STC, ASTC, IIC and AIIC. These metrics are commonly used across North America to measure the acoustic performance of a wall or floor assembly.
Currently the National Building Code has both requirements and recommendations when it comes to acoustics:
– Demising walls are required to achieve a minimum of 50 STC wall and to perform to a 47 ASTC (ASTC is the performance of the partition in the field, as tested in an actual construction).
– Separation between dwelling unit or hotel suite and an elevator shaft or refuse chute are required to achieve a minimum of 55 STC.
– All flooring assemblies are recommended to achieve a 50 IIC performance.
If you’re asking yourself what’s the difference between STC & ASTC and IIC & AIIC, you’re following along nicely. The 2015 NBC incorporated additional metrics: ASTC and AIIC. STC and IIC, are measurements of sound transmission loss calculated in an “ideal” lab environment. This is great for eliminating variables that can affect the numbers, but those lab tests can also give a false idea of how an assembly will perfom on site. Sound is like water, it easily transfers in all directions, including pathways which go “around” the wall or floor partition, known as flanking paths. All of these factors come into play with ASTC & AIIC, which determined through tests carried out on an actual construction site.
Now that we’ve gone over the basics of acoustics and the industry standards, you need to know a few acoustic tricks:
– Always seal gaps in your spaces to avoid sound leakage to other rooms.
– Decouple your wall assemblies to avoid sound vibrations directly transferring through rigid materials to the other side.
– Add absorptive wall panels to help with higher frequencies sounds.
– Always, always, always, take into consideration the impacts of acoustics in your construction. It’s always less expensive to do it properly from the beginning.
Having worked on many construction projects myself, I have tried to find materials out in the market to help with these kinds of sound problems. Recently, I learned about MSL, a manufacturer of soundproofing products for wall, ceilings and floors, all of which are easy to install. Their SONOpan panel is a dimpled wood-fibre board, which comes in 4’ x 8’ sheets and is installed in the wall behind the drywall. It sounds simple, but especially in wood-framed constructions, adding the SONOpan can be worth 10-15 additional STC points. That could easily mean the difference between hearing your neighbours easily and not hearing them at all! In addition, MSL also manufactures a range of membranes for use in the walls and floors. RefleXor is one of those membranes, gold in colour and coming in large rolls. To install, you simply staple it onto a base layer of drywall and finish with a top layer. The RefleXor being in between the layers provides decoupling, as well as sealing off small cracks, gaps and other imperfections which would otherwise lead to reduced sound performance. Thanks to that, it’s also a great odor, smoke and thermal barrier.
Lastly, when it comes to flooring in wood framed constructions, impact noise is a particularly tricky challenge. Often, a lightweight concrete or gypsum topper will be added to a subfloor to provide additional mass and increase the STC of the flooring assembly. However, this rigid material doesn’t provide as much of a benefit when it comes to impact noise, or IIC. To mitigate, it’s important to include an acoustic mat when using a concrete or gypsum topper. MSL’s product SONOpro effectively decouples the topper from the building structure, providing a large increase to impact noise insulation.
At the end of the day, it is very easy to design a wall or floor that should, in theory, hit code targets. However, once construction begins, it can become a different story. The realities and challenges of construction can often cause wall or flooring assemblies to perfom below expectations. That’s why, for every project it’s always important to choose the right materials, as well as a contractor who is aware of these challenges and has the experience and knowledge to address them. Stay tuned as we continue to bring more articles covering acoustic challenges, products, design tips and more!