Types of Roof & Roof Materials | Civil Engineering Optional Notes for UPSC PDF Download

What is Roof?

• A roof may be defined as the uppermost part of the building, provided as a structural covering, to protect the building from the weather (I,e from rain, sun, wind, etc). Structurally, roof is constructed in the same way as an upper floor, through the shape of its upper surface may be different.
• Basically, a roof consists of a structural element that supports the roof covering. The structural element may be trusses, portals beam, slab ( with or without beams), shells or domes. A roof covering may be A.C. sheets, G.I. sheets, wooden shingles, tiles, slates or slab itself.
• Roof and roof covering receive rain and snow more directly and in a greater quantity than do the walls. It must, therefore, provide a positive barrier to the entry of rain, and vigorous weatherproofing is most important.
•  At the same time, the roof structure, which supports a roof covering must have adequate strength and stability. Apart from these, a roof must have thermal insulation, fire resistance, and sound insulation.

Basic requirements of good types of roof are given below; 

• It should have adequate strength and stability to carry the superimposed dead and live load. 
• It should have effectively protected the building against rain, sun, wind, etc.
• It should be durable against the adverse effect of these agencies.
• It should have water-proof and should have efficient drainage arrangements.
• It should have provided adequate thermal insulation.
• It should have provided adequate insulation against sound. Most construction provided for a majority of building adequate insulation against sound from external sources.

Different Types of Roof

1. Pitched or sloping roofs.
2. Flat roofs or terraced roofs.
3. Curved roofs.

A selection of a type of roof depends upon the shape or plan of a building, climatic conditions of an area and type of construction materials available. Pitched roofs have sloping top surface.
These are suitable in those areas where rainfall/snowfall is very heavy. Broadly, building with limited width and simple shape can generally be covered satisfactorily by a pitched roof.

1. Pitched roofs or sloping roofs:- The roof with the sloping surface is called a pitched roof. Pitched roofs are basically of the following forms;
Types of pitched roof
(A) Lean-to-roof
(B) Gable roof
(C) Hip roof
(D) Gambrel roof
(E) Mansard or club roof
(F) Deck roof.

(B)Gable roof:- It is the common type of sloping roof that slopes into directions. Two slopes meet at the ridge. At the end face, a vertical triangle is formed.

(C) Hip roof:- A roof is formed by four sloping surfaces in four directions. At the end faces, slopes triangles are formed.

(D) Gambrel roof:- A roof, like a Gable roof, slopes in two directions, but there is a break in each slope. At every end, the vertical face is formed.

(E) Mansard roof:- This roof like a hip roof, slopes in the four directions, but every slope has a break. Hence, sloping roofs are obtained.

(F) Deck roof:- A Deck roof has slopes in all the four directions, like a hip roof, but a deck or plane surface is formed at the top.

Types of pitched roofs are; 

(a) Single roofs:- These roofs are consist of only a common rafter that are secured at the ridge ( to ridge beam) and wall plate. Single roofs are those which consist of only the rafter which is supported at the ridge and at the eaves.

 Such roofs are used only when the span is limited to 5 meters, otherwise, the size of the rafter will be uneconomical. The maximum span of the rafter is taken as 2.5m. Single roofs are four types; lean-to roof, verandah roof or she’d roof, couple roof, the couple closed roof and collar beam roof.

(b) Double or purlin roof:- The purlins give intermediate support to the rafter and are supported on end walls. An intermediate supports so provides in the form of purlin, reduces the size of the rafter to the economical range.

Such a roof is called a rafter and purlin roof. The rafter is provided fairly (40 to 60 cm). By supporting the rafter at its midpoint in this manner with a purlin, a span is halved, thus enabling the rafter to be made considerably lighter than it would need to be if it spanned the whole distance from eaves to the ridge.

2. Flat terraced roof:- This roof is the one that is either horizontal or practically horizontal with a slope less than 10°. Even a perfectly horizontal roof has to have some slope at the top so that rainwater can be drained off easily and rapidly. 

Similar to the upper floor, the flat roof can be constructed if flagstone, R.S.J., and flagstones, reinforced cement concrete, reinforced brickwork, jack arch roof or precast cement concrete units. However, the flat roof differs from the upper floor only form the point of view of the top finish, commonly called terracing, to protect it from the adverse effect of rain, snow heat, etc.

Following are the types of the terraced roof;

(A) Mud terrace roofing:- On this type of roof is suitable where rainfall is less. This can be provided either on tiles or wood board. In both cases, terracing is made with white Earth mud containing a large percentage of sodium salt.
(B) Brick jelly or Madras terrace roofing.

(D) Lime concrete terracing.
(E) Lime concrete terracing with tile paving.
(F) Bengal terracing roof.
(G) lightweight flat roof.

3. Curved roof:- Roof is an essential component of a pitched roof, to be placed over the roof framework, to protect it from rain, snow, sun, wind, and other atmospheric agencies.
Various type of roof material available and their selection depend upon; type of building, type of roof framework, initial cost, maintenance requirements, fabrication facilities, appearance and special features of the locality, durability, availability of the material itself and climate of the locality.
Following are the roof covering material commonly used for the curved roof; 
(A) Thatch covering.
(B) Wood shingles.
(C) Tiles.
(D) Asbestos cement sheets.
(E) Galvanised corrugated iron sheets.
(F) Eternit slates.
(G) Lightweight roofing.