In older commercial buildings with separate mechanical rooms, how should these spaces be treated during testing?

In older commercial buildings, separate mechanical rooms should be excluded from the test envelope during airtightness testing. This is because mechanical rooms typically contain systems that may not contribute to, or even compromise, the overall airtightness of the building envelope. Including these spaces in the test could lead to misleading results, as these rooms can have ventilated conditions necessary for proper operation of mechanical systems.

By excluding them, the focus remains on the actual building envelope, ensuring that the testing assesses the intended air barrier of the building. This practice helps in obtaining a more accurate representation of the airtightness of the conditioned spaces that will be occupied and used for the building's primary functions.