Sizes every gutter, downspout, scupper, conductor head and roof drain on a job to the 2021 IPC and IBC, all at once. It picks the downspout size, count and spacing for you, and prints a calculation package with the code section behind every check, plus a material list.

How to use it

• 1 Job. The job details and the design rainfall. Look the rainfall up with the NOAA link beside the field. Turn off any gutter or downspout sizes you don't stock, or add your own.
• 2 Roof areas. Add each part of the roof. A sloped roof drains to eave gutters: give each gutter run its length and the roof area that drains into it. A low-slope roof drains through scuppers or roof drains, with secondary (overflow) drainage. Results appear under each one as you type.
• 3 Results. The calculation package: every check with its code section, an outlet schedule and the material list. Print it, or save the material list as CSV.

What it decides

• Downspouts: for each gutter run, the fewest downspouts of each catalog size that pass, evenly spaced around any keep-outs you give (for example 0-4, 30-34 in feet from the left end), and the smallest gutter that carries the flow between them. It shows up to three choices; click one to use it.
• Scuppers: the opening width from the IPC's circumference rule, widened if needed so the water stays within the depth the roof was designed for, plus the conductor head and downspout under each primary scupper.
• Roof drains: the drain and leader size for the flow each one carries. Check the drain model's published flow rate against it.

How sizes are rated

Downspouts are rated from IPC Table 1106.3 and gutters from Table 1106.6. A size the table lists is rated directly. A size it doesn't list is rated as the best listed size with no more cross-sectional area. Where the table has no row at a gutter's slope, the next steeper row is reduced by the square root of the slope ratio, the relation the table approximately follows between its own columns. The package says which rule was used for each item.

Shortcuts

Ctrl+S	Save the job to a file
Ctrl+O	Open a saved job
Ctrl+P	Print the calculation package

Files

• Your job is kept in this browser as you work, until you press New job.
• Save writes one small .json file you can keep or send. Open reads it back on any computer.
• Print prints the Results tab, whichever tab you're on. Choose Save as PDF there for a PDF.
• Open the example job. It takes the place of the job that's open, so save yours first.

Check the results against the code your jurisdiction has adopted and against manufacturer data. Roof drain flow rates come from the drain manufacturer, and the roof's design water depth comes from the structural engineer. This tool reports the rain-load heads; it does not check the structure.

Free to use, provided as is, with no warranty: see the terms of use.