Returning to our completely average city of Normal, Illinois, we’ll keep the system’s roof angle at 40.5° for our calculations. As you can see in the table, the Normal house facing due south ...

Flat Roof Problems Water Drainage Issues. Due to their minimal slope, flat roofs are more prone to water ponding. Shingles are designed for pitched roofs, which allow water to run off easily.

The pitch of common roof rafters is designated by identifying the rise of the roof per foot of run. You may hear a carpenter say, “Your house has a 4/12 roof.” ...