Different types of timber sloping roofs are discussed below.
1. Lean to Roof
This is a roof which is usually used to cover verandah. This is used for spans up to 2.5 m. The roof covering is fixed to battens running across the rafters. It is usually constructed as a mono-pitched roof (Fig. 25.2).
Figure 25.2 Lean to roof
2. Couple Roof
This is a roof which has two rafters with a central ridge piece at the top. The rafters are fixed to the wall plates. The roof covering is fixed to battens running across the rafters. This can be used only up to spans of 3.5 m (Fig. 25.3).
3. Couple Close Roof
This is similar to that of couple roof and the rafters are connected by wooden tie. The tie has two functions: (i) prevents the outward spreading of the walls and (ii) acts as a support for any ceiling which might be fixed on it. This is suitable for spans up to 4.5 m (Fig. 25.4).
Figure 25.3 Couple roof
Figure 25.4 Couple close roof
4. Collar Tie Roof
This is similar to the couple close roof but with a difference that the tie (called collar) is fixed at a height of 1/2–1/3 of vertical height between the wall and the ridge. In order to gain the maximum strength the collar has to be placed as low as possible. This roof is suitable for spans of 4–5.5 m (Fig. 25.5).
Figure 25.5 Collar tie roof
5. King-Post Truss
For large spans, King- and Queen-post trusses are used. In king-post truss, the total weight of the roof is transferred to the walls vertically. The frame work of the truss is built such that the shape is not altered when loaded. Members in this truss are subjected either to compression or tension. The shape of the truss being triangular in shape gives a greater rigidity. Different load bearing members are parts of the King-post truss which are shown in Fig. 25.6. This type is suitable for spans of 6–9 m.
Figure 25. 6 King-post truss
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