Pitched roofs may broadly be classified into the following
Lean-to roof (verandah roof)
Collar beam roof or collar tie roof.
Double or purlin roofs
Triple-membered or framed or trussed roofs
King-post roof truss.
Queen-post roof truss.
Combination of king-post and queen-post trusses,
Mansard roof truss.
Truncated roof truss.
Bel-fast roof truss or latticed roof truss.
Composite roof trusses.
Steel sloping roof trusses.
Single Pitched Roofs
Single roofs consist of only community rafters which do secure at the ridge and also wall plate.
These are used when the span is weak so that no intermediate support is needed for the rafters.
This is the simplest type of sloping roof while which rafters slope to one party only.
A wooden wall plate is supported either on a steel corbel or a stone corbel, which are provided at 1 m middle to middle.
The wall plate is implanted on the opposite side, to the wall or pillars.
The difference in elevation between the two surface plates is so held that the coveted slope is obtained. The natural slope is 30°.
The common rafters are nailed to wooden partition plates on their upper end.
This type of roof is suitable for a maximum span of 2.5 m.
These are provided for sheds, outhouses attached to the main building, verandahs, etc.
This type of roof is formed by a couple or pair of rafters that slope to both sides of the ridge of the roof.
The upper ends of each pair of the rafter are nailed to a common ridge piece and their lower ends are notched and nailed to the wooden wall plates embedded in the masonry on the top of the outer walls.
Single couple roof is done when the span is limited so 3.6 meters.
Couple close roof
A couple of close roofs are similar to the couple roof, except that the ends of a couple of common rafters are connected by a horizontal member, called a tie beam, to prevent the rafters from spreading and thrusting out of the wall.
The tie beam may be a wooden member or a steel rod.
The connection between the wooden tie and the feet of the rafters is obtained by the dovetail halved joint.
Some couple-close roof is economically becoming for span up to 4.80 m.
Collar beam roof
When the spread increases, or during the load is more, the rafters of the couple nearby roof tend to bend.
This is avoided by raising the tie beam and fixing it at one-third back one-half of this vertical height from the wall plate so the ridge.
That raised beam is known as a single collar beam or collar tie.
This roof is suitable to an extent of up to 5 m.
Collar and scissors roof
It is comparable to the collar roof, except that to collar beam crossing is very different to have the appearance of scissors, is provided.
A double or purlin roof
A double roof is one in which purlins are introduced to support the common rafters at an intermediate point.
Before-mentioned roofs are used during the span exceeds 5 metres.
The function of a purlin is to tie the rafters together and to act as intermediate support to the rafters.
These roofs have two basic elements
The intermediate supports so provided in the form of purlins, reduce the size of the rafters to the economical range.
Each beam is thus supported at 3 points
At this bottom; on the wall into the wall plate,
At each top, near the ridge beam, and
In the middle by a purlin.
When the span of the roof exceeds 5 m and where there are no inside walls to support the purlins, then trusses are provided at suitable intervals along the length of the room.
Spacing is generally limited to 3.0 metres for wooden trusses.
A triplex branch or trussed roof consists of 3 sets of members
The purlins, which give intermediate support to the rafters, are themselves supported on trusses that are suitably spaced along the length of a room.
A trussed roof is provided during the length of each room is large.