Set the exterior budget,
then verify the load.

Exterior lighting answers to two mandatory tracks at once — a power allowance (C405.4) and a controls requirement (C405.2.6) over the same luminaires. This tool leads with the allowance so you can size a budget before specifying fixtures, then carries the project through connected-load verification. It informs decisions; it doesn't certify them.

About this tool. Allowances are read directly from base 2018 IECC Tables C405.4.2(1)–(3); controls follow C405.2.6 and the C405.2 parent exceptions. The allowance is two-level: base site allowance plus Table .2(2) surfaces form one freely-reallocatable pool; Table .2(3) features are fenced per application (unused allowance is forfeit, but the pool may top up a feature). Connected power is the simple sum of maximum rated watts — controls reduce utilization, not the count. This tool assumes new construction, does not model the Chapter 5 applicability gate, and is not a code review — verify against your jurisdiction's adopted edition and confirm interpretations with the AHJ before permit.

01 / SITE

Set the lighting zone

The lighting zone sets the base site allowance and scales every per-area rate. Pick the zone that matches the site description. Table C405.4.2(1) The code official may assign a different zone — flag the override if so.

Code-official overrideTable C405.4.2(1) The default zone above is the table reading for the site description. Tick this only if the AHJ has assigned the zone, and note it below.

02 / INVENTORY

Inventory illuminated areas

Enumerate every illuminated exterior application. Each maps either to a .2(2) tradable surface (added to the shared pool) or a .2(3) fenced feature (a use-it-or-lose-it allotment). Watch the unit — exterior allowances mix W/ft², W/linear-foot, and W-per-item.

Tradable surfaces Table C405.4.2(2)

Surface type Quantity

Fenced features Table C405.4.2(3)

Feature type Quantity

Trade asymmetry. Surface allowances are additive and freely reallocatable among each other — over-light the lot, under-light the walkway, as long as the pool total holds. A fenced feature's allowance can only fund its own luminaires; an unused portion evaporates. The pool may absorb a feature's overflow, never the reverse.

03 / BUDGET

Allowance budget

Your exterior allowance, decomposed. The pool is the base site allowance plus all tradable surfaces; fenced caps are each evaluated on their own. C405.4.2

04 / CONTROLS

Controls strategy

A parallel mandatory track on the same luminaires. C405.2.6.1 daylight shutoff applies to all exterior lighting; decorative lighting (façades, landscape) takes .6.2 after-hours shutoff, everything else takes .6.3 setback. Any time-switch used must meet the .6.4 device spec.

Per application. Choose a daylight-shutoff method and, where it applies, mark the control gate. Façade and landscape lighting are decorative by definition and route to .6.2 — the .6.3 setback is not available to them. Exemptions here follow the C405.2.6 exceptions plus the two C405.2 parent exceptions that reach outdoors.

05 / VERIFY

Connected-load verification

Enter each proposed exterior load at its maximum rated wattage and assign it to an inventoried surface or feature. Controls that dim or set back lighting do not reduce this count. C405.4.1 Exempt loads drop out of the power count; a dwelling-controlled load (#14) exits to R404.1.

Description Max rated W Assigned to Exemption

Gas-fired fixture Tick if the load being added is gas-fired — triggers the C405.4.3 electronic-ignition check.

06 / EXPORT

Export the record

Both exports read the live tool state — the same numbers shown above.

Design-phase report (.pdf)

Zone, allowance breakdown, controls schedule, and the verification verdict.

Inventory & verdicts (.xlsx)

Surfaces, features, loads, and the decomposed verdict, for project records.

Scope & reading notes. Locked to the 2018 IECC; 2018 C405.4 imposes no exterior source-efficacy requirement, so none is modeled. Two table values are reproduced as published: outdoor-sales open-areas Zone 4 prints at 0.05 W/ft² — below Zone 3 — and is flagged as a probable source erratum rather than silently corrected; stairways Zone 4 is 0.70 W/ft². Interior lighting (C405.2.1–.2.5, C405.3) is handled by the interior tools. The tool flags and routes the exemption-#14 dwelling-controlled peel-off to R404.1 but does not compute R404.1 itself.