Storm drainage and fuel gas are here. • Storm drainage — roof flow, storm drains, leaders and gutters (IPC Ch 11) • Fuel gas pipe sizing — natural gas and propane, all five materials (2021 IFGC Table 402.4) • Wet venting and combination waste & vent systems • Parallel pipe cutbacks — keep a bank of pipes in step through an offset • Water heater load, pump head, and expansion tank sizing • Area, perimeter, and tank fill / drain times • Pipe dimensions now cover 9 materials, from copper K through PEX • Hanger spacing, cleanout rules, and fixture clearances added to Reference • Capacity-used bar on drain sizing, so you can see the headroom Fixed: the inside diameter listed for 1-1/4" PVC Schedule 40 was 1.380", and is corrected to 1.360" per ASTM D1785. If you sized pipe volume, velocity or pressure drop on 1-1/4" PVC in an earlier version, those figures were about 3% off — worth re-running. Every result still cites the table behind it.