This study focuses on the airtightness of joints between light-wood-frame prefabricated wall panels typically used in Canada. Section 4.1 details the design and construction of the Rain and Air Infiltration (RAIN) Chamber test facility. Section 4.2 describes the testing and calculation methods. Section 4.3 describes the test specimen and materials. Section 5 provides the results and analysis. The results are divided into three parts: The increase in air flow due to penetrations in the drywall (Section 5.1) and the decrease in airflow due to external insulation overlap (Section 5.2) and water resistive barriers and tapes (Section 5.3). The results are used to develop a performance-based joint classification for this type of prefabricated panel system (Section 5.5). Analysis of the results also includes an assessment of the cost effectiveness of the airtightness measures (Section 5.4) and impact on energy performance and greenhouse gas emissions (Section 5.6).