Commercial Lighting Compliance
IECC 2018 — Section C405
Module · Daylight Area
C405.2.3 · Sidelit + Toplit Zones

Daylight Area Calculator

Build a room schedule from a design-phase export, assign daylight access, and size the sidelit (C405.2.3.2) and toplit (C405.2.3.3) daylight zones with reusable window and skylight families. The control matrix surfaces where daylight-responsive controls apply.

01

Project & room schedule

Start from a design-phase export, or add rooms by hand. Imported spaces arrive grouped by type; break a group out when each room needs its own glazing.

02

Daylight control matrix

Each room's daylight access drives which calculator applies. Toggle sidelit and toplit per room — that routes it into the tabs below. The control column flags daylight-responsive controls (C405.2.3) where daylight reaches a room from more than one cardinal direction. Click a row to edit that room.

Daylight-responsive controls (C405.2.3) are triggered, per code, by any sidelit or toplit zone carrying > 150 W of general lighting. This matrix deliberately surfaces that flag only for rooms with daylight from more than one cardinal wall — single-direction rooms are left quiet at your direction. Estimated zone wattage = net daylit area × the space-type LPD.

03

Window families

05

Export

Hand the program off to the Interior Compliance tool and keep a record of the daylight-zone work. The Excel carries a Space-by-Space sheet that uploads straight into the compliance tool's allowance step, plus a Daylight Zones sheet with each room's computed sidelit and toplit zone areas for the C405.2.3 review. The PDF is a design-phase summary.