Solving acoustical challenges in mass timber construction

by tanya_martins_2 | March 2, 2025 8:56 am

By Amanda Robinson

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Changes in the National Building Code (NBC) in 2020 laid the foundation for the rise of taller timber buildings, and the market has responded. According to a Natural Resources Canada (NRC) 2021 report,1 there were more than 750 completed or under-construction mass timber projects from 2007 to 2022, with a gross area of 2.9 million m² (31 million sf). B.C., Ontario, and Quebec are the leaders, hosting 87 per cent of Canada’s mass timber projects.

Sustainability is the primary driver of the shift to mass timber, since it is a low-carbon construction solution. The building sector is Canada’s third most carbon-intensive industry,² accounting for 22 per cent of emissions in 2022. Adopting more mass timber could cut embodied emissions in buildings by as much as 25 per cent. More progressive building codes, new products, and more innovative design possibilities are also driving the interest in wood.

Leading the way in B.C.

When it comes to mass timber, B.C. has always been leading, and it will continue to with updates to its building code in 2024 that enable new types of wood construction.³ B.C. owners and developers can build almost any type of building using mass timber, up to 18 storeys, and include restaurants, shops, care facilities, and warehouses. Ontario followed suit in January 2025 to also allow construction up to 18 storeys.

The code includes new encapsulation requirements tailored to the scale of the building. Encapsulated mass timber construction refers to buildings where the mass timber components must be surrounded by fire-resistive material. Encapsulation delays the exposure of the wood structure to a fire, but the recent B.C. code changes include some zero-minute fire encapsulation requirements for lower-rise buildings, except in critical areas such as exits, vertical shafts, and public corridors. This allows architects to expose the timber without violating fire codes.

Traditionally, mass timber projects have concrete in sections of the floor. The concrete serves multiple purposes: it helps acoustically by adding mass to improve sound reduction performance, helps structurally provide a diaphragm, and creates fire separation. However, the changes in the BC Building Code (BCBC) will allow for concrete-free mass timber buildings. Not pouring concrete on-site offers multiple benefits, including less carbon output, reduced project construction time and labour, and, as a result, lower costs.

While the “no concrete” option is more environmentally friendly, B.C. is in a more active seismic zone than other parts of the country, so reducing the mass of the building increases the stability if the ground shifts. Between the three aspects of acoustics, structure, and fire, the new BCBC has removed barriers to explore the benefits of adopting a “no poured concrete” design ethos.

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Moving to dry construction

Architects and designers are focused on net-carbon-zero buildings. Concrete provides mass that makes it easier to reduce sound transmission in mass timber buildings, but it is also one of the most carbon-intensive materials, contributing an estimated eight per cent of global carbon emissions.

In traditional mass timber builds, the structural floor would include concrete thick enough to prevent a certain amount of sound from getting into the floor and travelling to other spaces. Developers can use thinner concrete toppings; however, less concrete can create its own challenges. For example, a thin concrete topping going across three or four walls means sound flanking can occur. To keep the acoustics from being compromised, builders today would pour the concrete floors in a mass timber building in each section and then build a wall between them. This kind of jigsaw puzzle construction is more labour-intensive and more challenging to schedule.

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The new B.C. code finally broke the barrier of not requiring poured concrete in mid-rise buildings. However, as soon as the concrete is removed, a building needs workable acoustical considerations. A standard cross-laminated timber (CLT) alone will not provide sufficient sound reduction for residential construction that needs ASTC–47 or above. Even in the greenest building, tenants or owners do not want to hear what their neighbours are doing. To manage this, different build-ups can be used, and construction can incorporate more isolated layers and air gaps. Dry construction allows a floor build-up with plywood or precast, with the pieces laid on cementitious boards or other similar materials for greener solutions.

It is a common misconception that timber buildings require concrete floors for acoustics. Concrete is also not always required to meet fire code or structural needs. The move away from this common material means projects can re-examine how buildings are constructed.

Exposed timber, acoustically sound

Architects and designers want to showcase the beauty of mass timber, but it creates challenges acoustically. Builders and designers have to work really hard on all the junctions. And this is not the only consideration—sound isolation is one part of the acoustic puzzle with mass timber.

For Centennial College in Scarborough, Ont., the expansion of its A-Building achieved zero-carbon certification due largely to a highly efficient building envelope. It is now the first LEED Gold-certified zero-carbon, WELL-certified mass timber education facility.

The building incorporates sustainably harvested mass timber glulam posts and beams that support CLT floor panels. The CLT was exposed in the classroom areas, and a high level of sound reduction was achieved in the adjoining space through careful attention to the details and the damping provided by the concrete topping above. If the concrete toppings were removed in this instance, other design solutions would have been required for the same outcome.

The mass timber used throughout the project was designed to represent the spirit of the region’s woodlands, reflecting the natural setting of Highland Creek. However, achieving a nature-inspired interior involved a number of acoustical challenges. Within the building, Wisdom Hall is a cascade of terraces and stairs over multiple storeys, providing a bright and dynamic setting for students and visitors to gather and interact. The ceiling treatment included wood panels in different shapes and artwork to represent the flow of a river. It is a tall space with old wood that needed to be acoustically comfortable for all users.

In addition to looking at the sound reduction performance, the acoustically pleasing interior is esthetically pleasing. Custom wood baffles were used to create absorptive panels in the space. Working with the designers, acoustical engineers determined how many baffles were needed to incorporate absorption, while honouring the design and not interfering with the tale being told. This used a combination of custom acoustics baffles and acoustic wall panels, with the designers providing the shapes and spacing.

Acoustics baffles were evenly distributed across the impacted areas, with some baffles left untouched. For example, every other baffle on the second floor needed to be micro-perforated with tiny holes to improve acoustics. Since the baffles were integrated into the design, Indigenous artwork was also included as a feature piece of the building.

The domed room in Centennial’s Indigenous Commons room presented multiple acoustical challenges. Circular rooms are an important aspect of Indigenous architecture because they are inclusive. However, round rooms with curved walls cause challenges from an acoustical perspective. If the sound is not treated correctly, all of it comes back to the centre of the room. If people are within the focal point, they receive all the sound in the room but will not necessarily be able to understand it.

In addition, the designers wanted to acknowledge the arts of traditional indigenous people with the basket weave effect in the room. The spacing of the wood slots and the thickness were set to ensure the acoustics of the room worked with absorption materials incorporated behind the weave. The room also has a skylight box where much of the noise can be trapped. Creative acoustic design ensured that all aspects of the room could perform as intended.

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Holistic approach

Detailing is very important with a mass timber structure to achieve the ultimate design goals. Contract administration is a key component, since the pre-planning for mass timber buildings can include decisions that may be made for the sake of simplicity but add to acoustical challenges.

Selecting the supplier of the timber material early in the process is critical. This decision should be made as early as the acoustician and architect’s choices because engaging a team that can quantify the constraints from the beginning can save a lot of rework and wastage.

For example, at Centennial College, the CLT beams were designed and created very early in the process, and notches were added to provide a channel for items such as wires or plumbing. The notches were sized to accommodate a certain amount of penetrations, whether or not the entire notch size was to be used, so the design was flexible.

From an acoustical point-of-view, the holes provided challenges, and just putting sealant in them was not sufficient since some of the holes were fairly large. The solution was to cover both sides of the penetration with wood, drywall, or metal, and a closure plate with an oversized hole that could be sealed. In addition, insulation was added to the entire cavity to ensure that sound isolation through the larger opening was maintained. This was not an issue for beams in the middle of the room, but the penetrations in room boundaries needed to be covered.

With more push toward dry construction, more opportunities exist to explore how to expose timber; sometimes, creating a particular look will not be acoustically sound. Some cases may require finding the middle ground between design and acoustics. For example, trying to achieve STC–60 in a mass timber building with exposed beams is not yet possible. However, collaborating with all the project partners can help identify potential solutions early in the process to avoid fixing costly issues once the building is finished.

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Finding new solutions

Alternative dry construction toppings, such as fibre cement or heavy board materials on resilient underlays, have successfully been used on projects to achieve the required sound reduction without concrete. In addition, using rubber gaskets at construction joints helps reduce flanking paths.

Ceilings in commercial (non-residential) mass timber buildings can often be challenging since the architect often wants exposed wood. In these cases, dowel-laminated timber (DLT) can provide support. Created by stacking dimension lumber together on its edge or cross-laminating, each DLT plank is embedded with a cut-out that allows a dowel to connect them. There are versions of DLT that incorporate acoustic absorption into the DLT panel. However, other aspects of DLT need to be considered, and this solution may not be the ideal direction in many cases. With multiple considerations, a holistic approach to design is crucial.

What is next for mass timber?

In the early days of mass timber, it was a structural element covered with gypsum layers for fire safety and acoustical performance. This risk-averse approach is still the case, but as more people see the beauty in wood, there is an increased push for exposed timber because the industry has the solutions to make it work.

The code changes include hotels, dormitories, and apartment buildings, so mass timber could be important in expanding Canada’s housing supply. For example, HAVEN is a pre-fabricated, 12-storey mass timber overbuild solution for existing commercial buildings that is being considered by the Canada Mortgage and Housing Corporation (CMHC).⁴ It leverages the high strength-to-weight ratio of mass timber and is a purpose-built rental solution that could add up to 250 units per site.

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The guidelines also include assisted living, care facilities, and hospices. The next wave of mass timber will likely include hospitals, but it will need to consider the high standard of infection control requirements and vibration mitigation. For example, medical imaging equipment is vibration-sensitive, so it will be very challenging to build it with mass timber, but it is coming.

Acoustics must be part of the holistic design of any mass timber building. In the case of Centennial’s A Building, including baffles as part of the design is a creative way to address acoustics without just adding acoustical add-ons (also known as ‘acousticons’) everywhere. A more collaborative and holistic process can find solutions.
It is important to understand mass timber and how a space can sound great within the constraints of the materials.

The possibilities for mass timber are limitless. As the industry innovates, so do the design and construction. B.C. is the first province to adopt dry constructions; based on history, other provinces will follow suit. The key is finding the balance between showcasing the beauty of mass timber and ensuring the buildings are acoustically sound.

Notes

¹ Read more on mass timber construction in Canada, Natural Resources Canada (NRC), Government of Canada, natural-resources.canada.ca/our-natural-resources/forests/industry-and-trade/forest-productsapplications/mass-timber-construction-canada/23428

² See “Timber Rising: How Wood Can Spur Canada’s Green Building Drive,” Myha Truong-Regan, Royal Bank of Canada Thought Leadership, October 2023, thoughtleadership.rbc.com/timber-rising-how-wood-can-spur-canadas-green-building-drive/

³ Refer to “Advancing Mass Timber in BC Codes,” Office of Mass Timber Implementation, Province of British Columbia, gov.bc.ca/assets/gov/business/construction-industry/advancing_mass_timber_in_bc_codes_web.pdf

⁴ Review HAVEN: A 12-storey pre-engineered, prefabricated mass timber overbuild solution for existing buildings, Final Funding Recipients for Round 4 of the Housing Supply Challenge, Canada Mortgage and Housing Corporation (CMHC), cmhc-schl.gc.ca/professionals/project-funding-and-mortgage-financing/funding-programs/all-funding-programs/housing-supply-challenge/round-4-housing-supply-challenge/round-4-funding-recipients

Author

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Amanda Robinson, vice president of architecture at Aercoustics Engineering, follows her passion for architectural acoustics—seeing designs transform from concept to reality and listening to completed projects. Her 25 years of experience across three continents allow her to understand acoustic designs from many perspectives.

Source URL: https://www.constructioncanada.net/solving-acoustical-challenges-in-mass-timber-construction/

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