Can an entire oscillating roof deck area be used in the penthouse area limitation calculation outlined in Section 1510.2.2?
Further Clarified Question:
When a building’s roof oscillates to provide an aesthetically pleasing environment for the floor directly below the roof, is the “supporting roof deck” of the building’s penthouse floor area limited to only the roof deck portion directly below the penthouse or is the “supporting roof deck” permitted to be the entire area of the entire oscillating roof deck that covers the floor directly below?
Interpretation #9458
Published November 21, 2025
Original Request
- Code Version
- 2023
- Code
- BUILDING
- Code Description
- Chapter
- 15
- Section
- 1510.2.2
- Topic
- Penthouse
Question
Answer Published 11/06/2025 at 8:15 AM
Section 1510.2.2 limits the aggregate area of a penthouse and other enclosed rooftop structures to no more than one-third the area of the supporting roof deck. As a portion of this roof system is oscillating, the portion that actually moves should be removed from the overall supporting roof deck total as it would not actually support anything do to its movement. On the other hand, it is a roof, and part of the roof area total calculation and could be looked at under the total supporting roof deck for this restriction. This decision is up to the local AHJ as it would be their interpretation of the intent of "supporting roof deck" area.
Commentary
None.