How much slope does a flat roof need to have?

How much slope does a flat roof have to have on it

sachabeemer, the slope of the typical flat roof is anywhere between 0:12 to 3:12. Anything over 3 is labeled as steep slope. If you have a truly flat 0 rise roof, then you can install tapered insulation to create slope. In order to use the roof as anything other than a roof, such as a garden or deck area, then 1:12 is preferable. Are you installing a roof system or a deck system preparing for a roof?