Gutter with downspout on a steep-slope roof.

Gutter on a gravel-surfaced built-up roof. Removing loose gravel from the gutters is a common maintenance item with this type of roof.

Useful Links:

1. GeneralThe Wikipedia article here provides an accurate overview.

2. Codes: "1106.6 Size of Roof Gutters" from the 2015 International Plumbing Code. Available at the UpCodes website.

3. Maintenance: "General Inspection And Maintenance Of Gutters And Downspouts". Available on the website of the US General Services Administration

4. TechnicalA useful gutter sizing calculator is available at the website of NorthClad Rainscreen Solutions.

5. TechnicalGutters and Downspouts: Sample Gutter Sizing Calculation can be seen at the website of the Copper Development Association, and walks you through the process of determining the proper dimensions of a hypothetical gutter. (Table 4.4.2 - Rainfall Data and and Drainage Factors is viewable here).

6. Gutter manufacturers can be found here.