What is the minimum slope for a flat roof in building design?

Question

The building is approximately 50' in height. I've heard in the ballpark of 1/4" per ft but I would just like to know for sure. Provide any sources if possible. Thank you.

Answer 1

Metal desk roofing can be laid at a minimum of 3 to 5 deg pitch depending on the profile.
Concrete roof tiles or terracotta roof tiles can range from 18 to 35 deg again depending on the manufacturer's profile.
It is not the height but the area of the roof that is more important. You have to consider the amount of water that the roof has to drain away. And if you are designing for snow, then other factors like load has also to be considered.
You should look for metal deck roofing manufacturers web sites in your country as profiles vary in different regions.

Answer 2

NRCA has chosen the performance-based approach to positive drainage and not a prescriptive minimum roof slope value, such as 1/4-in-12 (1.2 degrees), because specific project conditions often affect roof assemblies' abilities to drain properly in a timely manner. For example, for buildings constructed with roof decks that truly are flat, installation of a 1/8-in-12 (0.6-degree) tapered installation system may be adequate to provide positive drainage.

On the other hand, roof structures and decks constructed with marginal finish tolerances, built-in camber or excessive load deflection may require more than 1/4-in-12 (1.2-degree) slope to achieve positive drainage.