Are there any general guidelines to follow to determine the number of downspouts that should be provided from a pitched, shingled roof? I’m assuming that roof area would factor into the calculation, but I’m sure that there are other factors like length of eavestroughs serviced.

I’m inspecting a house next week (new construction) that is about 3600 square feet in 2 storeys. I’m guessing that the total length of eavestroughs is 160 feet. The builder has provided one downspout. Seems to me that at least one more should have been installed.

Any comments appreciated.