Types of Pitched Roof

Pitched roofs that may  broadly be classified into the following

• Single roofs

1. Lean-to roof (verandah roof)
2. Couple roof.
3. Couple-close roof.
4. 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 also wall plate.
• These are used when the span is weak so that no intermediate support is needed for the rafters.

 Lean-to-roof

• 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°.
•  That common rafters are nailed to wooden partition plate on their upper end.
• This type of roof is suitable for a maximum span of 2.5 m.
• These are provided for shed, out-houses attached to the main building, verandahs, etc.

Couple roof

• This type of roof is formed by a couple or pair of rafters which slope to both the 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 close roof is similar to the couple roof, except that the ends of a couple of common rafters are connected by horizontal member, called tie beam, to prevent the rafters from spreading and thrusting out of the wall.
• The tie beam maybe a wooden member or a steel rod.
• The connection between wooden tie and feet of rafters is obtained by 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 have the tendency to bend.
• This is avoided with 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 up to 5 m.

Collar and scissors roof

• It is comparable so that collar roof, except that to collar beam crossing every different to have an appearance of scissors, is provided.

A double or purlin roof

• A double roof is the 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

1. Rafters, and
2. Purlins. 

• 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

1. At this bottom; on the wall into the wall plate,
2. At each top, near the ridge beam, and
3. At the middle by a purlin.

Trussed Roofs

• 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 interval 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

1. Common rafters,
2. Purlins, and
3. Trusses.

• The purlins, which give intermediate support to the rafters, are themselves supported on trusses which are suitably spaced along the length of a room.
• A trussed roof is provided during the length of each room is large.

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