2021 IECC Section C405
Lighting is allowed only so much power. Section C405.3 puts a ceiling on the interior lights, and Section C405.5 puts a separate ceiling on the exterior lights. In both cases the test is the same: add up what is installed, work out what the code allows, and make sure the installed number is not larger. This lesson covers how to count, the two ways to find the interior allowance, the exterior tables, and one full check. The controls that switch these lights off were Lesson 9. Local adoption governs which edition applies (see Lesson 1).
A building meets the interior rule when its total connected interior lighting power is not greater than its interior lighting power allowance (C405.3). Connected power comes from Section C405.3.1. The allowance comes from Section C405.3.2, using either the Building Area Method with Table C405.3.2(1) or the Space-by-Space Method with Table C405.3.2(2). The figure runs the whole check on an office building. The same idea applies outdoors under Section C405.5, with its own tables.
Use what the fixture actually draws. For a line-voltage lamp use the rated lamp wattage. For a luminaire with a ballast or transformer use the rated input watts of that ballast or transformer with the lamp. For an LED luminaire, with an integral or remote driver, use the rated luminaire wattage. Track, cable, rail, and plug-in busway are different because someone can add or move fixtures later without rewiring. For those, count the specified luminaire wattage but not less than 8 W per linear foot, or the wattage limit of the permanent current-limiting devices protecting the system, or the wattage limit of the transformer feeding it. Anything else counts at manufacturer data or another approved source (C405.3.1).
The code also lists 20 kinds of lighting that are left out of the total. The ones you will meet most often are exit signs, emergency lighting that is off during normal operation, advertising and directional signs, food-warming lights, lighting approved because of safety, retail display windows enclosed by ceiling-height partitions, furniture-mounted task lights with automatic shutoff, and display lighting in galleries or museums that is in addition to general lighting. When a takeoff looks high, check the list before you argue with the designer.
Pick the building area type from Table C405.3.2(1), multiply its floor area by the watts per square foot, and add the results if the building has more than one type. An "area" means all contiguous spaces that serve one building area type, so the corridors and break room inside an office building are part of the office. For a use the table does not list, pick the closest one (C405.3.2.1). Some rows from the table:
| Building area type | Allowed W per sq ft |
|---|---|
| Office | 0.64 |
| Retail | 0.84 |
| Religious building | 0.67 |
| Library | 0.83 |
| School or university | 0.72 |
| Health care clinic | 0.81 |
| Multiple-family (dwelling units excluded) | 0.45 |
| Warehouse | 0.45 |
| Parking garage | 0.18 |
Read the footnotes. For multiple-family, dwelling units are excluded, and neither their floor area nor their lighting watts are counted, so only corridors, lobbies, laundry rooms, and similar common areas go into the calculation. Dormitory and hotel rows carry similar notes where sleeping or dwelling units are excluded by Section R404.1.
A one-story office building has 8,400 square feet. Office is 0.64 W per square foot, so the allowance is 8,400 x 0.64 = 5,376 W. The lighting schedule shows 96 LED troffers at 36 W (3,456 W), 30 downlights at 18 W (540 W), 20 feet of lobby track counted at the 8 W per foot minimum (160 W), and 12 LED strips at 30 W in storage and mechanical rooms (360 W). Connected power is 3,456 + 540 + 160 + 360 = 4,516 W. Ten exit signs and the egress fixtures that stay off in normal operation are excluded. Because 4,516 W is not more than 5,376 W, the building passes with 860 W to spare. Connected power is 84 percent of the allowance, a number that matters in Lesson 11, where credit thresholds sit at 90 and 85 percent.
The whole-building tables are not always allowed. A project that covers only part of a building, such as one tenant suite or one floor of a rehab, must use Space-by-Space, and so must any building with unfinished spaces (C405.3.2). Define each space enclosed by partitions that reach at least 80 percent of the ceiling height, look up its space type in Table C405.3.2(2), multiply by its floor area, and add. A space with several functions can be split. Where both a common space type and a building-specific type are listed, the building-specific one applies (table note a). An unfinished space gets the lesser of its connected power or 0.2 W per square foot (C405.3.2.2). Some rows:
| Space type | Allowed W per sq ft |
|---|---|
| Office, enclosed | 0.74 |
| Office, open plan | 0.61 |
| Conference, meeting, multipurpose room | 0.97 |
| Corridor (otherwise) | 0.41 |
| Restroom (otherwise) | 0.63 |
| Storage room | 0.38 |
| Lobby (otherwise) | 0.84 |
| Religious building, fellowship hall | 0.54 |
Example: a tenant suite has 1,200 sq ft of open plan office, a 400 sq ft conference room, 300 sq ft of corridor, and 150 sq ft of restrooms. The allowance is 1,200 x 0.61 = 732 W, plus 400 x 0.97 = 388 W, plus 300 x 0.41 = 123 W, plus 150 x 0.63 = 94.5 W, for 1,337.5 W in all.
Space-by-Space users can earn extra allowance for specific lighting functions, but only where that lighting is installed and controlled as Section C405.2.4 requires, and only for those luminaires (C405.3.2.2.1). Lights installed in sales areas specifically to highlight merchandise get extra power from an equation that weights the sales area by product type: vehicles, sporting goods, and small electronics; furniture, clothing, cosmetics, and artwork; and jewelry, crystal, and china each earn more than other goods. Decorative lighting, or lighting for art and exhibits, added on top of general lighting may add up to 0.9 W per square foot in lobbies and 0.75 W per square foot in other spaces. The Building Area Method has no such add-ons.
Connected exterior power is the total maximum rated wattage of all lighting powered through the building's energy service (C405.5.1). Exclusions include lighting approved for safety, emergency lighting that is off in normal operation, exit signs, signage, athletic playing areas, temporary lighting, lighting for pools and water features, and lighting highlighting art, monuments, or the flag. The allowance starts by choosing a lighting zone from Table C405.5.2(1), unless the code official specifies one: Zone 1 is developed parks and rural areas, Zone 2 is predominantly residential zoning and neighborhood business districts, Zone 3 is all other areas, and Zone 4 is high-activity commercial districts in major cities. Add the base site allowance to the watts from each area type in Table C405.5.2(2) (C405.5.2). Selected rows:
| Item | Zone 1 | Zone 2 | Zone 3 | Zone 4 |
|---|---|---|---|---|
| Base site allowance | 350 W | 400 W | 500 W | 900 W |
| Parking areas and drives, per sq ft | 0.03 | 0.04 | 0.06 | 0.08 |
| Walkways under 10 ft wide, per linear ft | 0.50 | 0.50 | 0.60 | 0.70 |
| Entrances and exits, per linear ft of opening | 14 | 14 | 21 | 21 |
| Entry canopies, per sq ft | 0.20 | 0.25 | 0.40 | 0.40 |
Example, a community clinic in Zone 3: base site 500 W, plus 12,000 sq ft of parking at 0.06 = 720 W, plus 150 ft of walkway under 10 ft wide at 0.60 = 90 W, plus 12 ft of entrance openings at 21 = 252 W. The exterior allowance is 500 + 720 + 90 + 252 = 1,562 W. Pole lights, wall packs, and canopy lights on the building service must total no more than that. Table C405.5.2(3) adds separate allowances for specific uses such as drive-up windows (200 W each) and building facades (none in Zone 1), and those extra watts may be used only for the luminaires that serve those uses (C405.5.2.1).
Two short rules close the section. At least 95 percent of permanently installed plant growth luminaires must deliver at least 1.6 micromoles per joule (C405.4). Gas-fired lighting appliances may not have continuously burning pilots (C405.5.3).
In the field
A GCHS rehab turns a church annex into a Group B community office. Plan review first asks which method the designer used. If the whole building is being altered the Building Area Method is allowed, but if only the fellowship hall is being redone the project must use Space-by-Space. In the field the inspector compares the luminaire schedule with the lighting form: LED wattages match the driver labels, track is counted at 8 W per foot or more, only exit signs and egress fixtures that stay off are left out, the floor area on the form matches the drawings, and every exterior pole light fed from the building panel is in the exterior total.
1. A new Group B office building has 10,000 square feet, all one office area. What is its interior lighting power allowance by the Building Area Method in 2021 IECC Table C405.3.2(1)?
2. A new 6,000 square foot retail store is checked by the Building Area Method. What interior lighting power allowance does Table C405.3.2(1) give?
3. An inspector reviews a submittal for a tenant improvement that renovates one 2,400 square foot suite in a multi-tenant Group B building. The designer used the Building Area Method. What is the problem under Section C405.3.2?
4. A lobby has 30 linear feet of plug-in lighting track. The luminaires specified for it total 90 W, and a current-limiting device rated at 600 W protects the track. Using the first track option in Section C405.3.1, how many watts count toward connected power?
5. A lighting takeoff for a Group B office lists 64 LED troffers, 14 downlights, 9 exit signs, and 6 decorative wall sconces. Which item may be left out of total connected interior lighting power under Section C405.3.1?
6. A designer draws 7-foot partitions between a private office and an open area under a 10-foot ceiling and treats the office as its own space under the Space-by-Space Method. Does Section C405.3.2.2 allow that?
7. Under the Space-by-Space Method, a tenant suite has 1,200 sq ft of open plan office, a 400 sq ft conference room, 300 sq ft of corridor, and 150 sq ft of restrooms. Using Table C405.3.2(2), what is the allowance?
8. A shell building for a future clinic has 5,000 square feet of unfinished space with 1,500 W of connected lighting. What allowance applies to that space under Section C405.3.2.2?
9. Under the Space-by-Space Method a Group B lobby of 400 square feet gets extra decorative lighting, added on top of the general lighting and controlled as required. What is the most extra power allowed by Section C405.3.2.2.1?
10. A new three-story Group R-2 building has 30,000 square feet in total, of which 24,000 is dwelling units and 6,000 is corridors, lobby, laundry, and stairs. What is its Building Area Method allowance from Table C405.3.2(1)?
11. A clinic in Lighting Zone 2 has 15,000 square feet of parking and drives and no other exterior area that earns an allowance. What is its exterior lighting power allowance under Table C405.5.2(2)?
12. In Lighting Zone 2, a walkway 6 feet wide and 200 feet long serves the entrance of a community center. What does Table C405.5.2(2) allow for that walkway?
13. In Lighting Zone 3, a building has two pedestrian entrances, and each opening is 6 feet wide. What entrance allowance does Table C405.5.2(2) give?
14. GCHS is rehabilitating a community center in a neighborhood business district surrounded by residential zoning, and the code official has not specified a lighting zone. Which zone does Table C405.5.2(1) point to?