Clear span frames require no interior support beams which allow for unobstructed use of the entire interior space of the building. Clear span frames can be gable symmetrical (double-sloped with the ridge in the center of the building and both eaves having the same height), gable asymmetrical (double-sloped with the ridge off-center and both eaves having either the same OR different heights), or single slope (single-sloped with no ridge and both eaves having different heights).
Gable symmetrical is the most common and with a higher roof pitch, can provide a significant amount of overhead space to allow for car lifts or framing out of additional space for loft/storage use. Single slope is common in areas with heavy rain or snowfall, because they allow the roof to shed excess rain and/or snow to one side. Additionally, single slope is ideal for retail buildings where a mansard or parapet is desired for a more aesthetically pleasing entry.
The Leanto frame attaches to and is partially supported by the main building frame. They are typically a single slope design and have straight sidewall columns. While a leanto frame can follow the existing building roof slope, most leantos are below eave. A below-eave leanto off each side of a fully enclosed building and running the entire length of the building would create what is commonly referred to as a monitor or raised center barn style building.
Leantos are expensive as they complicate both the engineering of the building that they are being attached to as well as the foundation engineering of the project. Additionally, in high snow load areas, leantos create the potential for loads caused by drifting snow at the point where the leanto attaches below-eve to the main building. For customers simply looking for roof-only shelter for equipment, an inset bay designed building is a more cost-effective alternative.
Modular frames make use of interior load-bearing columns to more evenly distribute the load of the entire building. A modular frame works very well for projects that require extremely large steel buildings. The addition of an interior, or intermediate column on wider buildings, especially those with high snow loads helps reduce the size of the rafter and column, making the project more economical.
Besides being a traditional architectural style, Gambrel Frame offers aesthetic and practical advantages. Roofs that spring from the first-floor wall plate, the way gambrels and capes do, rather than from the second floor. Such roofs are more interesting and visually pleasing. But the gambrel has some advantages over the cape: in particular, gambrel allows more useful space within the framed volume.