One building contains a restaurant on the ground floor and office suites on the floors above, each with its own occupant load. How does the plumbing code determine the number of fixtures required for that building?
- AThe occupant loads are added together and the ratio for the predominant occupancy is applied to the total
Choosing a predominant occupancy discards the ratio that applies to the other use, and the restaurant is usually the one that suffers.
- BThe higher of the two ratios in the table is applied to the combined occupant load of the whole building
Applying the strictest ratio to everyone overbuilds the low-demand portion substantially and is not what the table directs.
- CThe ratio for the occupancy with the greater floor area is applied to the combined occupant load
Floor area does not decide which ratio governs. A small restaurant can generate more fixture demand than a large office floor.
- Each occupancy is computed at its own ratio and the resulting fixture counts are added together
Why D is correct
Each occupancy is evaluated on its own terms because the ratios exist to capture how a particular use behaves. Computing separately and then adding preserves that logic and produces a count that works for both parts of the building.
What this question is testing
Whether the candidate can apply the minimum facilities table across a mixed occupancy building rather than collapsing it to a single ratio.
On the job
Mixed-use buildings are the normal case in downtown work, and the fixture count drives how much core space the restrooms consume on every floor. Doing the arithmetic by occupancy also tells you where the fixtures have to be located, since facilities generally have to serve the occupancy they were counted for rather than being pooled at one end of the building. Get this settled before the core is laid out.
Memory technique
Count each use on its own ticket, then add the tickets.
Exam tip
Separate the uses, run the table once for each, then add. Never average occupancies together.
Where to look it up
IPC Chapter 4, minimum plumbing facilities and Table 403.1, including the provisions on multiple occupancies and where required facilities may be located. The UPC's occupancy breakdown differs, so use your adopted code.