A 24-unit, 4-story apartment building case study — full fixture unit takeoff, a tapered domestic water riser sized floor by floor off Hunter's Curve, two DWV soil stacks sized to avoid an oversized single stack, and a lead-lag hot water plant with a worked recirculation loop calculation.
The project brief: a developer needs a complete plumbing design for a 24-unit apartment building — 6 one-bedroom units per floor across 4 floors, each with a kitchen and one bathroom, plus a shared laundry room. Every downstream sizing decision in this module traces back to one fixture unit takeoff done correctly per unit and building-wide.
This module walks the whole design the way a real plumbing engineer would: the WSFU/DFU takeoff per unit and for common-area fixtures, a riser that tapers floor by floor as cumulative demand drops, the case for splitting DWV into two soil stacks instead of one oversized stack, and a worked BTU-based recirculation loop flow calculation for the central hot water plant. The full worked numbers, complete bill of materials, and finished design reasoning are part of the unlocked module below.