Aercoustics Engineering Ltd was retained by SWL Canopy Corp to provide acoustic design and testing services for the Façade Prototype Design project. The acoustic design goals for the project are:
1. Achieve industry standard indoor-outdoor sound isolation with a mass timber façade system, and
2. Comply with the acoustic performance requirement in the International Building Code (IBC) and National Building Code (NBC) for interior sound isolation in residential buildings,
To determine the required building facade designs, a range of acoustic tests were performed on sample panels between November 2021 and May 2022. The acoustic tests consisted of:
1. Outdoor-indoor sound isolation tests in Hood Canal, Washington, to establish in field conditions
2. Laboratory tests at Intertek in Lake Forest, California, to establish acoustic performance according to certified industry test methods for ultimate reliance. Overall, each of the façade panels demonstrated a level of sound isolation that complies with the acoustic requirements in both the IBC and NBC for multi-family residential buildings, and the system is suitable for use in most urban environments.
Indoor-outdoor sound isolation in residential buildings is critical to occupant comfort and quality of life. To achieve an acceptable interior sound level in a typical urban environment, a minimum façade sound isolation rating of STC-35 or OITC-28 is required (lab rated). Lower sound isolation ratings are acceptable in quieter environments, while higher ratings will be required for buildings located next to loud noise sources, including highways, transit lines, and airports, to adhere to applicable local requirements. The indoor-outdoor sound transmission tests performed on the façade system resulted in lab rated values of STC-35 to 36 / OITC-29 to 32, and field-tested values of AOITC-24 to 28. As field tested values are typically up to five points lower than lab rated values for the same panels, these results showed that the façade system as-built provides the right level of indoor-outdoor sound isolation for use in a typical urban environment. Multiple types of windows and doors and various interior furring wall assemblies were tested. These tests have been used to design options for the façade panels that can achieve indoor-outdoor ratings between STC-25 to 45, making the system suitable for a wide variety of acoustic environments.
The effect of a building’s façade system on the interior sound isolation between adjacent rooms is important as large format lightweight façade panels can transmit a significant amount of sound energy horizontally between rooms in a building, ultimately limiting the sound isolation between adjacent residential units. This occurs from sound flanking through a panel that spans across two or more residential units.
To address the impact of the façade system on the interior sound transmission, the performance of the façade system was assessed using a combination of airborne noise measurements and vibration measurements. These tests demonstrated that the joints between the façade panels prevent a significant amount of sound transmission, and allow for the direct exposure of mass timber elements within the space as long as the joints align with the demising walls and floors.
Where the façade panel joints can align with demising walls and floors, the timber finish can remain exposed on the interior and exceed the building code requirement for sound isolation between adjacent dwelling units. When these façade joints do not line up with the demising walls, or higher STC and ASTC ratings are required for other reasons, the performance can be improved using a variety of gypsum board furring wall assemblies on the inside face of the façade panels. Based on the test results, a number of design options have been presented to achieve ratings up to ASTC-60