The roof is an important element in the house and serves the basic purpose of the house i.e., providing shelter. The roof is classified into two main types, i.e. flat roof and pitched roof. The pitched roofs are also of two types:
Single Roof is defined as a roof having only a single slope on each side of a central ridge, whereas, in shed roof, it has a single slope, but without a central ridge.
The single roof is a type of sloping roof. In this type of roofs, common rafters are provided on each slope without any intermediate support. Single roof construction is simple than other roofs.
In the single roof, each rafter is supported at two points:
01. At the bottom; on the wall through wall plate
02. At the top; by the ridge
Single roof has some limitations. Single roof is used for small spans. If greater spans are used, then larger roof sections are needed. In single roof, if rafter feet are not tied together by means of a roof joist or binder, then this roof will have a tendency ,under weight ,to push the supporting walls outwards at top causing structural failure of the wall. Hence in larger span of roof, single roof is not recommended.
The various forms of single roof are as follows:
The lean to roof is defined as single slope roof with its upper edge adjoining a wall or building.
In double roof, each rafter is supported at three points:
The basic elements of the double roof are rafters and purlins. In Double Roofs, if length of span is larger, then it requires an intermediate support. This support is usually a beam which is protected under the rafters at a point between the ridge and the wall plate. This beam is known as purlin. Purlin is used to reduce the size of the rafters and to make structure in economical one. Double roof construction is simple than other roof.