Form or Function: Why do commercial buildings commonly have flat roofs while residential has sloped?

Okay, there’s a lot of parts to this.

Either a commercial or home could have either a sloped roof or flat roof if that was important to either.

Commercial buildings that are larger that chose a sloped roof would end up with a very large structure as the roof. If this didn’t serve additional functions it would just be a large waste of space and materials.

A lot of commercial buildings use the roof to mount loud or hot equipment. While this does occur in houses it happens much less. Flat roofs make this easier.

There is a general assumption that commercial buildings will have a greater amount, or at least a more knowledgable amount, of maintenance. This plays a part in the roofing design decisions. A sloped roof will shed water in all cases. A flat roof requires that the drains be checked periodically and cleaned. Also, with equipment people are more likely to check. It may be only once a year on commercial buildings, but have you been on your house roof even in the last few years?

Aesthetics play a large part. Houses tend to have attractively styled roofs. Commercial buildings may have partial roofs for this purpose, but large sections are never seen and therefore efficient only.

Lastly, there a laws that dictate a lot of different aspects. Heights, what can be seen from the street, the roof may be required to have specific properties due to location or use.

I could keep going, but I’m sure you get the idea. It is both a matter of form and function and most building designers, architects, engineers.. have come to similar decisions when it came to construction.