Section 5.1/Natural Ventilation Design
ASHRAE 62.1 Section 5.1 covers using natural ventilation as the primary strategy including opening area and distance requirements.
Natural ventilation may be used as the sole ventilation method when the design meets specific criteria. Openings to the outdoors must have a total free area of at least 4 percent of the net occupiable floor area. The ventilated space must be within 25 feet of an operable opening. Environmental conditions (outdoor air quality, temperature, humidity, noise, security) must be acceptable for the building occupants during the periods when natural ventilation is relied upon.
Why this section exists
Natural ventilation through operable windows and openings can provide adequate outdoor air without mechanical systems in suitable climates. However, it depends on outdoor conditions (temperature, wind, air quality) that are not always favorable. The requirements ensure that natural ventilation can actually deliver adequate outdoor air to all occupied areas during the conditions when it will be used, and that mechanical ventilation is available when conditions are not suitable.
What plan reviewers look for
Plan reviewers verify the 4 percent opening area by checking the window schedule for operable area and comparing it to the floor area. They check that no point in the occupied space is more than 25 feet from an operable opening. They also check whether the building has mechanical ventilation available for periods when natural ventilation is not feasible (extreme temperatures, high humidity, poor air quality).
Common violations
Related ASHRAE 62.1 requirements
Section 6.2 covers the mechanical ventilation procedure used when natural ventilation is not the primary strategy. IMC Section 401.2 covers the parallel natural ventilation provisions in the mechanical code. Section 5.2 covers engineered natural ventilation systems.