When Should Title 24 Calculations Be Done on a Commercial Project?

While the lighting and mechanical design can still change — not after the drawings are finished. The calculations frequently tell you something has to move, and that is much cheaper to act on before the set is issued.

Early enough to change the design

The most common commercial failure is a lighting scheme designed purely for effect, then handed over for compliance. Retail and hospitality run close to the power allowance by nature, and the fix — more efficient fittings, fewer of them, or reallocating power between general and accent lighting — is a design change, not a paperwork change.

Run early, the calculation is a design input. Run late, it is a rework instruction.

The date that fixes which rules apply

Compliance is assessed against the code edition in force when the permit application is submitted, and the 2025 edition applies to applications from 1 January 2026. A project straddling a cycle change should know which edition it will be assessed under before the documents are prepared, because a set produced under the previous edition does not automatically carry across.

What has to be settled first

Less than people assume. A floor plan with the use of each space named, a lighting schedule with input wattages, and a statement of what the mechanical scope touches is enough to start. A finished permit set is not required and is arguably too late.

Where equipment is undecided, the calculation proceeds on an assumption — and if the installed unit differs, the documents stop describing the building.

The item that has to be planned earliest

Acceptance testing, even though it happens last. Where lighting controls or mechanical systems are in scope, a certified technician has to test them on site before the permit closes, and lighting and mechanical are separate certifications. Identifying that at design stage is a short conversation; discovering it at final inspection is a hold on the permit.