What is a defining feature of Quonset Greenhouses?

The defining feature of Quonset greenhouses is their structure, which is characterized by straight sides and a half-circle top. This semicircular design not only provides a sturdy construction but also allows for maximum light penetration and effective air circulation inside the greenhouse. The shape helps to distribute wind and snow loads evenly, making it suitable for various climatic conditions.

While the other options feature different structural designs, they do not accurately represent the unique arching shape of a Quonset greenhouse. The option that indicates framed using arches pipes describes a different type of greenhouse, while the third option pertains to tilted roofs typical of other designs. The last option suggests a simplicity that does not encompass the distinctive arching half-circle form that defines Quonset greenhouses.