Butterfly roofs were developed in 1933. It was an original American roof design typically used in urban areas in the mainland United States and also in Hawaii. This type of roof was developed as part of the overall architectural effort to bring a more modern look and feel to American family homes.
In particular, butterfly roofs have two side-by-side pieces that are placed in such a way that the outsides of the roof are angled upward and the mid-section of the roof is angled downward. The general appearance is such that when one looks at the roof, it resembles the distinctive V-shape of butterfly wings flapped upward. This is why it is called a "butterfly roof."
The butterfly shape of the roof enables the windows in the house to be taller than usual. Since the windows are taller, that enables more sunlight to come through into the house. During the daytime, this can create a more open and airy aesthetic inside the house.
There are various types of butterfly roofs one could choose for a house. For example, there is the shed roof, which has one flat gable and one gable angled like a butterfly wing. Also, there is the saddle roof, which has curved angles that point downward. There is the zigzagging roof that has more than one butterfly roof placed side-to-side such that some of the points face upward and some downward.
Another example of a butterfly roof is the gable roof, which includes a triangle-shaped roof with one of the gables being longer than the other. There's the low-pitch roof which has a slope of 30 degrees or less. Then there is a marina-style roof, which has a round center with upward-pointing outer parts. Other types of butterfly roofs can be designed according to the homeowner's specifications.
The butterfly roof design has some weaknesses. For instance, if there is any kind of leak or block in the drainage system, it does tend to result in weaker pillars that cannot hold as much weight. That is one reason butterfly roofs are not more widely used.
Granted, butterfly roofs are useful in the sense that they can enable the homeowner to capture rainwater. The inverted gable is what causes the butterfly roof to be able to capture rainwater. Also, rainwater harvest systems are put into the basement to facilitate the capture of rainwater in the house that the homeowner can use for drinking water, for showering, for watering the garden, or for any other purpose for which water is needed inside of the house.