What is the flattest a roof can be and still use standard asphalt type 3 tab shingles. When is roll roofing required?
The normal minimum for 3 tab composition roofing is 4" in 12" (4/12). Most roofing manufacturers allow for a 3/12 pitch with some special installation requirements.
Some roll roofing may be allowed on 'flat' roofs, but 1/12 is the normal minimum. For more information, see the Roofing selection Guide.
The most important question re: minimum pitch is related to the manufacturer's guidelines. The basic guidelines can be found on the material wrapper, the details should be available in a longer written document at the point of purchase. By following those guidelines you should be protected by the manufacturers warranty - George