ROOF DEFINATION

ROOF

Roof is the upper most portion of the building which protects the building from rain, wind and sun.

Various types of roofs used may be divided broadly into three types:

1. Flat roofs 2. Pitched roofs

3. Shells and folded plates.

Flat roofs are used in plains where rainfall is less and climate is moderate. Pitched roofs are preferred wherever rainfall is more. Shells and folded plate roofs are used to cover large column free areas required for auditoriums, factories etc. Brief description of these roofs is presented below:

1. Flat Roofs:

These roofs are nearly flat. However slight slope (not more than 10°) is given to drain out the rain water. All types of upper storey floors can serve as flat roofs. Many times top of these roofs are treated with water proofing materials-like mixing water proofing chemicals in concrete, providing coba concrete. With advent of reliable water proofing techniques such roofs are constructed even in areas with heavy rain fall.

The advantages of flat roofs are:

(a) The roof can be used as a terrace for playing and celebrating functions.

(b) At any latter stage the roof can be converted as a floor by adding another storey.

(c) They can suit to any shape of the building.

(d) Over-head water tanks and other services can be located easily.

(e) They can be made fire proof easily compared to pitched roof.

The disadvantages of flat roofs are:

(a) They cannot cover large column free areas.

(b) Leakage problem may occur at latter date also due to development of cracks. Once leakage problem starts, it needs costly treatments.

(c) The dead weight of flat roofs is more.

(d) In places of snow fall flat roofs are to be avoided to reduce snow load.

(e) The initial cost of construction is more.

(f) Speed of construction of flat roofs is less

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Types of Flat Roofs:

All the types listed for upper floors can be used as flat roofs.

2. Pitched Roofs: In the areas of heavy rain falls and snow fall sloping roof are used. The slope

of roof shall be more than 10°. They may have slopes as much as 45° to 60° also. The sloped roofs are known as pitched roofs. The sloping roofs are preferred in large spanned structures like workshops, factory buildings and ware houses. In all these roofs covering sheets like

A.C. sheet, G.I. sheets, tiles, slates etc. are supported on suitable structures. The pitched roofs are classified into

(a) Single roofs (b) Double or purlin roofs

(c) Trussed roofs.

(a) Single Roof:

If the span of roof is less than 5 m the following types of single roofs are used.

(i) Lean to roofs (ii) Coupled roofs

(iii) Coupled-close roof (iv) Collar beam roof

In all these roofs rafters placed at 600 mm to 800 mm spacing are main members taking load of the roof. Battens run over the rafters to support tiles. Figure 8.13 shows various types of single roofs.

(b) Double or Purlin Roofs:

If span exceeds, the cost of rafters increase and single roof becomes uneconomical. For spans more than 5 m double purlin roofs are preferred. The intermediate support is given to rafters by purlins supported over collar beams. Figure 8.14 shows a typical double or purlin roof.