Depths use product units (inches or millimetres from the page Units control). The server converts to millimetres for the LPS SWMM model.
Retention roof
Honeycomb: not applicable
Green roof
Honeycomb: not applicable
Honeycomb is described as porosity in product terms. In SWMM, the detention layer uses a STORAGE row with void ratio, not porosity.
This tool only adjusts thickness in SWMM; void ratio stays at the model default (0.98).
Storage thickness sent to SWMM is 2 × (honeycomb + 0.2″) (product convention for how SWMM treats storage).