In the interior of a building, finishes and details tend to confuse the structural framework of the building. The comparatively simplicity of a porch, however, provides a chance to showcase the elegant design of the structure’s framing. An open gable porch seizes that opportunity and shows off its structural skeleton.
Ridge and Rafters
The basic constituents of a sloping roof are rafters that slope downward on either side of the roof, forming a summit at the center, and a ridge that runs along that summit and supplies the rafters something to rest against. In a traditional sloping roof, the ridge does not provide any structural support for the roof; it is simply a surface to the upper ends of the rafters are nailed, and the weight of the roof is transmitted down through the rafters to support poles below.
Posts and Beams
In the case of a sloping roof over an enclosed building, the lower ends of the rafters rest on the exterior walls of the building. Within an open porch, nevertheless, the rafters rest on horizontal beams that are supported by vertical columns or posts. The required dimensions for the posts and beams depend on the size and weight of the roof, but beams made from doubled two-by-eights or two-by-tens resting on four-by-four or six-by-six poles are typical.
Because the weight of the roof is moved down through the sloping rafters, the force exerted by the weight tends to push the support poles or walls of the porch outward. Ceiling joists that run horizontally from 1 side of the porch to another tie the bottom ends of the rafters together and resist this force. Within an interior space, the ceiling joists are generally completed with wall board to separate the attic distance from the space below, but at an open sloping porch, the joists could be left open to the room beneath the roof.
Cathedral Ceiling and Structural Ridge
Removing the ceiling joists leaves the porch with an open cathedral ceiling, but it requires that the structural support of the joists be replaced with some other structural alternate. The most frequent option, a structural flux, is a comparatively heavy beam that runs along the roof’s ridge and can be supported at its ends by load-bearing poles. The weight of the roof rests on the ridge beam instead of on the lower ends of the rafters, and the weight is moved through the poles, either to the other beam that is supported by other posts, or all the way to the bottom, where the pole rests on a concrete footer.