California Green Building Code (CALGreen) – Temporary ventilation

During construction it is adequate to provide ventilation to reduce risks to health from air contaminants or lack of oxygen. It is important that the components of the ventilation system should not themselves present additional risks to those constructing the building.

CALGreen Code Section 5.504.1: Temporary ventilation.

The permanent HVAC system shall only be used during construction if necessary to condition the building or areas of addition or alteration within the required temperature range for material and equipment installation. If the HVAC system is used during construction, use return air filters with a Minimum Efficiency Reporting Value (MERV) of 8, based on ASHRAE 52.2 1999, or an average efficiency of 30 percent based on ASHRAE 52.1 1992. Replace all filters immediately prior to occupancy or, if the building is occupied during alteration, at the conclusion of construction.


The intent of this requirement is to allow limited use of the permanent heating and cooling system during construction and requires the use of air filters with a MERV of 8. It is intended to control air pollutants for workers during construction and ensure good air quality for occupants when the building is turned over to the owner. It allows ventilation using air-conditioning systems when necessary, though this practice is noted not to be an optimum choice due to possible damage to equipment that may jeopardize a warranty. The California Energy Code, Part 6, CCR, contains ventilation standards for conditioned spaces. Title 8, CCR contains additional regulations for worker safety.

Compliance Method:

Engineers and designers should include in the construction documents the method for protecting the duct openings and mechanical equipment during the construction phase. The contractor is responsible for employing the prescribed methods of compliance and should be able to demonstrate that the practices are being followed during construction if requested by the enforcing agency.


Plan intake: The plan reviewer should confirm that the construction documents show the methods to be implemented to meet the code requirements’ listed practices to be followed by the contractor.

On-site enforcement: The inspector should verify that duct openings for installed mechanical systems are protected from dust and that mechanical equipment filters are replaced with new filters as applicable.

(Excerpted from ‘Guide to the 2019 California Green Building Standards Code Nonresidential’ – Chapter 5)

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