California Green Building Code: CALGreen – Carbon dioxide (CO2) monitoring

Providing adequate ventilation to the habitable indoor spaces is crucial to the health and wellbeing of the occupants. Fans supplying and exhausting air from these spaces can consume large amount of energy, so it is essential to strike a balance between ventilation and energy use. Often code requires ‘Demand Control Ventilation’ to minimize energy use. In such circumstances it becomes critical to monitor the amount of carbon dioxide in the spaces to make sure they are not under ventilated. This is a mandatory CALGreen code measure. The code language is as follows. 

CALGreen Code Section 5.506.2: Carbon dioxide (CO2) monitoring. 

For buildings or additions equipped with demand control ventilation, CO2 sensors and ventilation controls shall be specified and installed in accordance with the requirements of the 2019 California Energy Code, Section 120.1(c)4.


When demand control ventilation is required by the California Energy Code, this provision intends to maintain CO2 levels that are within the range that established and recognized as safe for human occupancy. The current edition of the California Energy Code, Section 120.1(c)4, identifies the sensors, controls and devices required to keep CO2 emissions to established levels.

Compliance Method:

Design team: Specify and show CO2 sensor locations in the construction documents.

The contractor should install the specified equipment to ensure that it is operating as designed.


Retain product data sheets for on-site verification by the enforcing agency and for the Operation and Maintenance Manual.


Plan intake: The plan reviewer should confirm that the construction documents show the CO2 sensors and that they meet the requirements of Part 6.

On-site enforcement: The inspector should verify that the complying sensors displaying readings are installed per the construction documents. Confirm that the readings are recorded as required by the California Energy Code.

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

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