How to Meet Acoustical Requirements While Reducing Embodied Carbon

27 Nov How to Meet Acoustical Requirements While Reducing Embodied Carbon

On April 29, 2019, the City of Vancouver declared a climate emergency. At the same time, the municipality announced “six big moves” to reduce the city’s carbon pollution and build on previous efforts to promote clean, climate-friendly systems and projects in Vancouver.

One move mandates lower carbon construction materials and designs. The goal is to reduce the embodied emissions from new buildings and construction projects by 40% compared to a 2018 baseline. According to City Council’s report, this big move could reduce carbon emissions by 78,000 tonnes. The City aims to achieve this by 2030.

To make this big move, designers will need to select building materials with lower embodied carbon, while still achieving the acoustical criteria in the City of Vancouver Building Bylaw performance requirements.

Building Materials, Embodied Carbon, and Acoustical Performance

Embodied carbon can vary among different building systems—i.e., concrete, steel studs, or mass timber. Yet choosing the system with the lowest embodied carbon doesn’t mean sacrificing acoustical performance. It’s entirely possible to meet acoustical performance requirements for a project and also achieve the goal of reducing embodied carbon.

To illustrate how various acoustical assemblies affect the embodied carbon of a building, we calculated the embodied carbon of four different wall systems that have a Sound Transmission Class (STC) rating of 50, which is the Vancouver Building Bylaw’s requirement for party walls. Each wall assembly uses different materials, and thus each has a different level of embodied carbon. The four wall assemblies are:

Steel Stud

• 1 layer of 16mm (⅝”) Type X gypsum drywall
• 31 mm (1¼”) x 92 mm (3⅝”) 25 ga steel studs spaced at 400 mm (16″) or 600 mm (24″) o.c.
• 89 mm (3½”) fibreglass batt insulation
• 25 mm (1″) air space
• 89 mm (3½”) fibreglass batt insulation
• 31 mm (1¼”) x 92 mm (3⅝”) 25 ga steel studs spaced at 400 mm (16″) or 600 mm (24″) o.c.
• 1 layer of 16 mm (⅝”) Type X gypsum drywall

Wood Stud

• 16 mm (⅝”) Type X gypsum drywall
• 38.1 mm (1.5″) x 92 mm (3⅝”) wood studs spaced at 400 mm (16″) or 600 mm (24″) o.c.
• 89 mm (3½”) fibreglass batt insulation
• 25 mm (1″) air space
• 89 mm (3½”) fibreglass batt insulation
• 38.1 mm (1.5″) x 92 mm (3⅝”) wood studs spaced at 400 mm (16″) or 600 mm (24″) o.c.
• 16 mm (⅝”) Type X gypsum drywall

Concrete

• 150 mm concrete tilt up

Cross-Laminated-Timber

• 16mm(⅝”) Type X gypsum drywall
• 90 mm Cross Laminated Timber Panel
• 25 mm gap
• 92 mm steel stud
• 89 mm (3½”) fibreglass batt insulation
• 16 mm (⅝”) Type X gypsum drywall

We performed a Life Cycle Assessment (LCA) using One Click LCA in order to estimate the equivalent mass of CO₂ per square metre (kg CO₂e per m²) for each assembly. For our calculation, we have used a building life of 50 years.

Here are the wall assemblies ranked from highest embodied carbon to lowest:

• concrete – 63 kg CO₂e per m²
• mass timber – 27 kg CO₂e per m²
• steel stud – 24 kg CO₂e per m²
• wood stud – 16 kg CO₂e per m²

According to the US EPA, the average carbon emissions for a typical car is 4,600 kg CO₂ eq. per year. For a low-rise building with a floor area of approximately 3,600 m² (e.g., a 6-storey low-rise) the difference in embodied carbon between using concrete internal walls and wood stud walls would be the same as taking 15 cars off the road for a year.

Here to Help

Do you have a party wall assembly that is not listed here? We’d be happy to have a conversation with you about the embodied carbon trade-offs, and ensure that you are meeting the acoustical requirements for your project.

Of course, wall assemblies aren’t the only thing you need to worry about to meet either the Vancouver Building Bylaw or the BC Building Code. For more about the latest changes to the code, check out this post.

Written by Forest Borch and Brigette Martin