States and other jurisdictions regulate the energy-efficient design of commercial buildings with energy codes. The majority are based on the International Energy Conservation Code (IECC). This model code is updated every three years, with the latest version released in August 2024. With energy codes continuing to become increasingly stringent and most states basing theirs on the IECC, the 2024 release of the IECC is significant, as adoption is highly likely to replace legacy versions of the code in the future in various states.
The IECC limits lighting power density while adding a mandatory lighting controls layer to ensure lighting is automatically reduced when it is not needed. The 2024 version reduces lighting power allowances, expands mandatory lighting control requirements, creates an enhanced energy efficiency option for demand response, removes the luminaire-level lighting control (LLLC) compliance path, and issues clarifications.
In this column, I will break down what’s new compared to the 2021 version.
Scope: The IECC applies to various energy-using systems (including electric lighting) installed in new construction, additions, and alterations of buildings. The 2024 IECC removed the code exemption for projects involving the replacement of less than 10% of interior luminaires in an alteration and added one for exterior projects adding or altering up to 400 watts.
Lighting Controls (C405.2): Conceptually, the code seeks to limit energy consumption by automatically reducing or turning off lighting when it is not being used based on three inputs: occupancy, a time event, or ambient light level. In the 2024 version, the LLLC compliance path has been removed. Previously, the code offered compliance based on a discrete approach and a theoretically more direct LLLC approach. LLLC still offers a way to comply with code requirements, but it is no longer a separate formalized path.
Occupancy Sensing (C405.2.1): Occupant sensors can be used to satisfy the code’s automatic shutoff requirements. In the 2024 version, data-center computer rooms, laundry/washing areas, and healthcare facility supply rooms and telemedicine rooms have been added to the list where sensors are specifically required.
Time-switch Controls (C405.2.2): Where occupant sensors are not installed, time-switch controls must be installed and programmed to automatically turn off the lights when the space is predictably unoccupied. The control system must have certain capabilities. New to the 2024 IECC, the controls must be programmed to turn the lights off at least 12 hours per day for spaces where schedules aren’t available.
Dimming Controls (C405.2.3): Manual controls must be provided that allow users to control lighting and provide light reduction. The 2024 IECC eliminates bi-level switching as an option and requires continuous dimming in spaces ranging from classrooms to lobbies to offices. The dimming controls must be manual and provide continuous dimming from full output to 10% of full power or lower plus off. Manual controls must be placed where they are readily accessible and the controlled lighting visible to users or otherwise indicate the area and status of the lights.
“The 2024 release of the IECC is significant, as adoption is highly likely to replace legacy versions of the code in the future in various states.”
Daylight-responsive Controls (C405.2.4): The code requires that general lighting in daylight zones be reduced in response to available daylight. The 2024 IECC reduced the wattage threshold for requiring these controls. If there is more than 75 watts of general lighting in the primary or secondary side-lit daylight zones, or if there is more than 150 watts in these zones combined, daylightresponsive control is required. What’s more, the calculated exception to daylight-responsive controls in trade for lowering the lighting power allowance was removed, and an exception was added for enclosed offices spaces fewer than 250 sq ft.
Horticultural Lighting (C405.2.5): Lighting for nonvisual applications such as plant growth must be served by an independent timeswitch control. However, note that Section C405.4 in the 2024 IECC states that the luminaires in greenhouses must be controlled by a device that turns off luminaires in response to daylight.
Sleeping and Dwelling Unit Controls (C405.2.10): The 2024 IECC created a new special section for sleeping and dwelling units and consolidated all control requirements there.
Additional Energy Efficiency Requirements (C406): Buildings complying with the IECC must enhance energy efficiency by acquiring credits for implementing various stretch energy efficiency options listed on a table with applicable credits. This section has been thoroughly revised and expanded in the 2024 IECC to delineate requirements by building size. For lighting, options include energy monitoring, highend trim lighting controls, occupant sensors installed in more applications and with a 10-minute time delay, reduced lighting power, demandresponsive lighting controls, and automated shading. Note that the credit for enhanced digital lighting controls has been removed.
Demand-responsive Lighting Controls (C405.2.8): Demandresponsive lighting controls are covered as an enhanced energy-efficiency option in C406 and in Appendix CI103.1, which requires at least 75% of the interior floor area in specific building occupancy categories to have demand-responsive lighting controls. This appendix is not mandatory and is subject to adoption as an ordinance by the jurisdiction to be effective as a requirement. In either scenario, if demand-responsive lighting controls are installed, Section C405.2.8 becomes active. It requires these controls be capable of reducing the output of controlled lighting down to 80% or less of either full power or full output after receiving a demand-response signal from a certified virtual end node. If high-end trim is implemented, the trim level is considered “full power” or “full output.” The lights should be continuously dimmed over a period up to 15 minutes to reach the demand response level. After the demand-response event ends, the controlled lighting must return to normal operation.
Functional Testing and Documentation (C408.3): The IECC requires project commissioning to ensure all installed building systems operate as specified. This includes functional testing for lighting controls as well as certain documentation. The 2024 IECC adds functional testing requirements for automatic receptacle controls and, if installed, high-end trim controls and demand-responsive lighting controls.
COMMERCIAL BUILDING ENERGY codes continue to become increasingly stringent regarding lighting and controls while evolving with technological change, and the 2024 IECC follows this trend. In the future, commercial building energy codes may focus on energy consumption, system integration, and decarbonization rather than initial design power and control capability. In the meantime, the 2024 IECC is likely to be widely adopted and used by jurisdictions.
Lighting practitioners in jurisdictions likely to implement the 2024 version of the IECC should start to become familiar with its requirements, as there are some significant changes, particularly regarding lighting and controls. For more information, consult 2024 IECC by purchasing it at shop.iccsafe.org.
Gary Meshberg, LC, CLCP, LEED-AP, Member IES, is chair of the Lighting Controls Association (a council of NEMA) and strategic projects sales director, Building Control Systems for Legrand North America.