When adding plumbing to a stacked apartment unit:
- Start with riser space and fitting clearance.
- Code sizing comes second.
Piping Workflow Roadmap
The workflow runs in seven phases with two hard gates. Phase 4 is the pivot: everything above it is reused, so problems found in later phases are fixed in the prototype one-level pattern and re-run.
Key Design Considerations
Start with Sizing and Clearances - Will the Proposed Layout Fit?
Consideration | What to decide or check | What the sample project showed |
Riser chase size | Clear width and length for every stack plus fitting bodies; one chase per wet core | Bath chase was about 6" wide; branches could only enter risers along the chase's long axis |
Fitting clearance | Measure the actual elbow and tee families before setting riser spacing | A 3" PVC sanitary tee's branch hub reaches about 8" from centerline; copper tees about 4-3/4" |
Stack order | Order risers so branches and garage trunks reach them without crossing | Kitchen risers ordered HW, CW, Vent, SAN west to east so trunks never cross |
Tee spacing on stacks | Vertical gap between branch tees on the same stack | 3" sanitary tees need at least 8" between centers; base elbow plus lowest tee needs about 9" |
Then, Consider These Additional Factors That Impact Your Design Options
Consideration | What to decide or check | What the sample project showed |
Fixture connectors | Family connector sizes, directions and heights; whether all fixtures are true plumbing fixtures | Dishwasher was Specialty Equipment with no CW or vent connector |
Code and sizing | Fixture units, stack and branch sizes, trap-arm length, vent sizing and connection height above flood rim | Sizes were provisional; vents connected at 4'-0" to 5'-2" AFF |
Drain slope | 1/4" per ft on branches 3" and smaller; space below slab for the fall | Drains were modeled level; slope still to add |
Venting | Individual, common or wet venting; where each vent rises; vent-through-roof or AAV | Vents rose in walls and chases; roof terminations not yet modeled |
Water distribution | Supply direction (up-feed or down-feed), HW return, shut-offs per unit, hammer arrestors | Up-feed from a garage trunk; no HW return or valves yet |
Materials | Water piping (Copper L, PEX), DWV (PVC, cast iron for noise or fire rating) | Copper L water; PVC DWV and vent by default |
Rated walls and slabs | Penetrations through rated corridor and party walls; firestopping; sleeves | Several runs sat in 2-hour walls and will need firestop details |
Structure and coordination | Slab thickness, beams, ducts, sprinklers, electrical below the floor | 12" slabs; trap arms ran just under them |