Roof construction

Roof construction

An assemblage to provide cover for homes, buildings, and commercial, industrial, and recreational areas. Roofs are constructed in different forms and shapes with various materials. A properly designed and constructed roof protects the structure beneath it from exterior weather conditions, provides structural support for superimposed loads, provides diaphragm strength to maintain the shape of the structure below, suppresses fire spread, and meets desired esthetic criteria.

Modern roof construction usually consists of an outer roofing assembly that is attached atop a deck or sheathing surface, which in turn is supported by a primary framework such as a series of beams, trusses, or arches. The shape of the roof and type of roof construction are usually determined by, and consistent with, the materials and deck of the primary structure underneath. See Arch, Beam, Truss

Roof shapes include flat; hipped, where two sloping deck surfaces intersect in a line, the ridge or hip; pyramidal, which involves three of more sloping planes; domed, or other three-dimensional-surface, such as spherical, parabolic, or hyperbolic, shells; and tentlike, which are suspended fabric or membrane surfaces.

A roof assembly is a series of layers of different materials placed on and attached to the roof deck. Each type of roof assembly—related to protection against water entry from rain, snow, or ice; and insulation for temperature change, fire propagation, wind uplift, and moisture migration—has its own design requirements and methods of construction and attachment.

A roof is built upward from the structure below. The framework, or primary structural components, rest on the walls and columns of the structure, and these support the roof deck or the sheathing, which in turn carries the roofing assembly. The walls and columns may have girders framing into them. Beams rest on or are connected to girders. The roof deck or sheathing, the components that provide the basic support for the roofing assembly, span between and are anchored to the primary structural framing.

Long-span roofs are use space trusses, usually, of steel; but reinforced-concrete domes or other shell shapes, including folded plates, may be employed. In cable-supported roofs, the primary framework is composed of cables in tension that are slung between separate posts or from the top of the surrounding building perimeter. Tentlike or membrane roofs are a special application of a cable-supported roof. Air-supported roofs utilize a waterproof coated fabric that is inflated to its rigid shape by developing and maintaining a positive air pressure inside the structure, which keeps the roof surface under tension. Tennis-court “bubbles” utilize this design. See Buildings, Reinforced concrete, Structural steel