Code Change Summary: A new exception was added to recognize installations where concrete separates the roof decking from the wiring methods underneath.

Section 300.4(F) was added during the 2008 NEC^® development process to require cables and raceways installed under the roof decking to have at least 1 ½ inches of space between the under side of the roof decking and the wiring method. This is to ensure that future roof replacement does not result in roof deck screws or other fasteners penetrating the roof and the wiring methods underneath the roof deck.

In 2011, this section was revised to include boxes and the required measurement changed to 1 ½ inches.

In 2014, Section 410.10(F) was added to include similar language for luminaires installed under the roof decking.

In the 2023 NEC^®, a new exception was added to address installations where concrete is poured at the roof deck level. For these installations, the concrete provides the necessary protection for the raceways, wiring methods, boxes, and luminaires installed directly under the roof decking.

In the 2023 NEC^®, new exception 2 in Section 300.4(E) allows raceways, cables, and boxes to be installed without any spacing restrictions where metal-corrugated sheet roof decking is covered with a at least 2 inches of concrete slab, measured from the top of the corrugated roofing.

A similar change also occurred in Section 410.10(F) for luminaires installed under the same circumstances.

Below is a preview of the NEC^®. See the actual NEC^® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2023 NEC^® edition of NFPA 70.