Roof Drainage

Roof leaders (downspouts) at primary thru-wall scuppers. Note how the secondary (overflow) scuppers are higher than the primary scuppers.

Here poor drainage leads to ponding water along the gutter edge of this low-slope roof. Ponding water can speed up the deterioration of the roofing material.

Useful Links:

1. General: "Roof Drainage - Not My Problem...Maybe" by John Lawson is a very readable although sometimes highly technical article on the necessity of adequate roof drainage and the potential consequences of inadequate drainage. It's available at the Digital Commons section of the California Polytechnic State University website.

2. Codes: The "Roof Drainage" section of the 2015 International Building Code. Available at UpCodes.

3. Codes: The "Roof Drainage" section of the 2015 International Residential Code.

4. CodesThe roof-relevant sections of the 2012 International Plumbing Code. Available at UpCodes.

5. Drains: See here.

6. Gutters: See here.

7. Inspection of roof drainage systems: Mastering Roof Inspections: Roof Drainage Systems, Part 1 at the International Association of Certified Home Inspectors' website is worth taking a look at. Part two of this inspection guide can be accessed from this page.

8. Scuppers: See here.

9. Technical: Siphonic Drains: "The Fundamentals of Siphonic Roof Drainage System Design" is an easy-to-read introduction to this space-and-material-saving drainage innovation. Available to read on the website of Ron Blank & Associates, Inc. 

10. See here for drainage component manufacturers.