The one-table answer
| Requirement | 2021 IECC (R404) | 2024 IECC (R404) |
|---|---|---|
| High-efficacy lighting | All permanently installed fixtures, except kitchen appliance lighting | All permanently installed luminaires: 45 lm/W (luminaire) or 65 lm/W (lamp). Exceptions: appliance lamps, antimicrobial lighting, DOE-regulated general service lamps, luminaires 3 W or less |
| Interior controls | Dimmer, occupant sensor, or control built into the fixture. Exempt: bathrooms, hallways, exterior fixtures, safety/security lighting | Habitable spaces: manual dimmer OR automatic shutoff within 20 minutes of vacancy. Garages, unfinished basements, laundry and utility rooms: automatic shutoff required. Exempt: safety/security lighting only |
| Exterior controls | Same in both editions. Where total exterior lighting power exceeds 30 W: manual switch that permits automatic shutoff, automatic shutoff when daylight is present, override returns to automatic within 24 hours | |
| Lighting power density (W/ft²) | Not a residential requirement in either edition. Commercial only (C405) | |
| Continuous dimming 100% to 10% | Not a residential requirement in either edition. Commercial only (C405) | |
What did not change: 100 percent high-efficacy
The jump to 100 percent happened in the 2021 edition. Older editions phased it in: 50 percent in 2009, 75 percent in 2012 and 2015, 90 percent in 2018. The 2021 IECC (R404.1) requires every permanently installed lighting fixture, except kitchen appliance lighting, to contain only high-efficacy sources. The 2024 IECC keeps 100 percent and restates it in lumens per watt: a luminaire capable of 45 lm/W, or a lamp capable of 65 lm/W, with a short list of exceptions (appliance lamps, antimicrobial lighting, DOE-regulated general service lamps, and luminaires drawing 3 W or less).
In practice this is a non-issue for new construction. Any LED downlight, surface fixture, or screw-in LED lamp clears both numbers. Where it bites is the plan review: the electrical or reflected ceiling plan needs a note or schedule showing the fixtures are high-efficacy, or the reviewer has nothing to check.
What changed: interior lighting controls
2021 IECC R404.2 says permanently installed fixtures must be controlled by a dimmer, an occupant sensor control, or another control installed or built into the fixture. It exempts bathrooms, hallways, exterior fixtures, and safety or security lighting.
2024 IECC R404.2 splits the requirement by room type:
- Habitable spaces (R404.2.1): a manual dimmer, or an automatic shutoff control that turns the lights off within 20 minutes after the space is vacated and includes a manual on/off.
- Garages, unfinished basements, laundry rooms, utility rooms (R404.2.2): automatic shutoff within 20 minutes of vacancy, with a manual on/off. A dimmer alone does not satisfy this.
- Exception: safety or security lighting. The 2021 bathroom and hallway exemptions are gone.
The practical change for a builder: bathroom and hallway fixtures now need a control too, and the four "specific locations" need a sensor, not just a dimmer. The cheapest compliant path in most houses is a dimmer in every habitable room and a vacancy sensor switch in the garage, laundry, utility, and any unfinished basement.
Exterior lighting: the 30-watt line
Both editions use the same threshold. If the total permanently installed exterior lighting power is more than 30 W, R404.3 requires a manual on/off switch that permits automatic shutoff, automatic shutoff when daylight is present, and any override to return to automatic within 24 hours. A pair of 12 W LED porch fixtures totals 24 W and is under the line; add a 15 W garage flood and you are over it. A photocell or an astronomical timer at the panel covers the daylight requirement.
The confusion worth clearing up: residential vs commercial
Search results and AI answers about "2024 IECC lighting changes" are mostly about the commercial chapter. The 2024 IECC did reduce lighting power allowances and did add a requirement that dimming controls be continuous from 100 percent down to 10 percent. Those are in Section C405, which applies to commercial buildings and to residential buildings four stories and taller. They do not apply to a detached house, a duplex, or a townhouse, which fall under Chapter 4 [RE] and Section R404.
If a correction letter on a single-family permit cites a W/ft² lighting allowance or a continuous-dimming requirement, the reviewer has applied the wrong chapter. That is worth a polite reply with the section number. If a design guide or an AI answer tells you your house has an LPD limit, it is repeating the commercial provisions.
What a plans examiner checks
- A fixture schedule or a general note stating all permanently installed luminaires are high-efficacy (R404.1)
- Under 2024: control type per room, with dimmers in habitable spaces and automatic shutoff in garage, laundry, utility, and unfinished basement (R404.2)
- Total exterior lighting wattage, and a control note if it exceeds 30 W (R404.3)
- Which edition the jurisdiction has adopted. Many jurisdictions are still on 2021 or earlier; the 2024 control rules only apply where 2024 is in force
Sources
2021 IECC Sections R404.1, R404.2, R404.3 and 2024 IECC Sections R404.1, R404.2.1, R404.2.2, R404.3.1 as published in the corresponding IRC Chapter 11 [RE] (N1104), read on UpCodes and ICC Digital Codes. Commercial provisions referenced: IECC Section C405. Confirm the adopted edition and any state amendments with your building department; state amendments override the model code.
Travis Smith, ICC-Certified Residential Energy Inspector / Plans Examiner. The same certification your building department's plan reviewer holds - working for you.