Building Structures Illustrated by Francis D. K. Ching & Barry Onouye & Douglas Zuberbuhler

Author:Francis D. K. Ching & Barry Onouye & Douglas Zuberbuhler
Language: eng
Format: epub
ISBN: 9781118848302
Publisher: Wiley
Published: 2015-07-30T12:00:00+00:00

ROOF STRUCTURES

Roof structures, like floor structures, are horizontal spanning systems. However, while floor structures provide flat and level platforms for the support of our activities and furnishings, roof structures have a vertical aspect that can dramatically impact the exterior form of a building as well as the quality of the spatial volumes beneath their canopy. A roof structure may be flat or pitched, gabled or hipped, broad and sheltering, or rhythmically articulated. It may be exposed with edges flush with or overhanging the exterior walls, or it may be concealed from view, hidden behind a parapet. If its underside remains exposed, the roof also transmits its form to the upper boundaries of the interior spaces below.

Because the roof system functions as the primary sheltering element for the interior spaces of a building, its form and slope must be compatible with the type of roofing—shingles, tiles, or a continuous membrane—used to shed rainwater and melting snow to a system of drains, gutters, and downspouts. The construction of a roof should also control the passage of moisture vapor, the infiltration of air, and the flow of heat and solar radiation. Depending on the type of construction required by the building code, the roof structure and assembly may have to resist the spread of fire.

Like floor systems, a roof must be structured to span across space and carry its own weight as well as the weight of any attached equipment and accumulated rain and snow. Flat roofs used as decks are also subject to live occupancy loads. In addition to these gravity loads, the planes of the roof may be required to resist lateral wind and seismic forces, as well as uplifting wind forces, and transfer these forces to the supporting structure.

Because the gravity loads for a building originate with the roof system, its structural layout must correspond to that of the column and bearing wall systems through which its loads are transferred down to the foundation system. This pattern of roof supports and the extent of the roof spans, in turn, influences the layout of interior spaces and the type of ceiling that the roof structure may support. Long roof spans would open up a more flexible interior space while shorter roof spans might suggest more precisely defined spaces.

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