A roof covering is a material which is placed over a sloping roof to give protective surface. The primary function of the covering is to prevent the direct entry of heat, rain and snow into the building. Choice of roofing material depends on the type of roof structure, local conditions, cost, the type of building, etc. Different types of roof coverings for sloping roofs are discussed below.
1. Thatch
It is one of the most ancient and simple type of roof covering used in rural areas. It is used because of its abundant availability, cheap cost and need of unskilled labour. Thatch is either from straw or reed. Thatch is less resistant to fire, unless it is treated by a fire proofing material.
2. Slate
It is basically a sedimentary rock which could be split into thin sheets. Slates are available in different natural colours. Most common colour is various shades of grey. A good quality slate should have (i) even colour, (ii) be hard, (iii) impervious and (iv) should give a ringing sound when struck. It should not be tough and have white patches.
The sizes of slates vary from 60 cm × 35 cm to 25 cm × 12.5 cm and the thickness varies from 1.5 to 4.5 mm for smaller sizes and 10 to 12 mm for large sizes. There are various methods of fixing slates (Fig. 25.8).
Figure 25.8 Methods of fixing slates
3. Tile
Like thatch, tile has been in use from olden days. The sizes and shapes have improved from time to time. Clay tiles are made similar to bricks. Concrete tiles are used to a limited extent.
Plain tiles are of sizes varying from 25 cm × 15 cm to 28 cm × 18 cm with thickness varying from 9 to 15 mm. These tiles are used along with special tiles such as hip and valley tiles.
Pan tiles are made of clay and it is the oldest type. The roof is covered by the use of bent tiles. This is comparatively less weight. The tiles are of sizes 30–35 cm in length and 20–2.5 cm width. There is little chance of leakage at joints.
Mangalore tile is one of the most popular type of patented tiles. These tiles are machine-pressed clay tiles which have better interlocking, enabling better protection against heavy rains.
Asbestos cement tiles of square or rectangular in shape are also in use. These tiles can be laid on boards of the roof or directly on the battens which are nailed to the rafters. Figure 25.9 shows the fixing details of asbestos cement (AC) tile.
Figure 25.9 Fixing of AC tiles
4. AC Sheet
The combination of cement and asbestos produced in different sizes and shapes form the asbestos cement sheets. Asbestos cement sheets are available as corrugated roofing sheets and as well boards. This type of roof covering has several advantages, viz., durable, not heavy, impervious, fire and vermin proof, less labour cost, etc. These sheets are fixed on wood or steel purlins (Fig. 25.10).
Figure 25.10 AC sheets
5. CGI Sheets
Corrugated Galvanised Iron (CGI) sheets is yet another type of roof covering widely used although the appearance is not that good. Like AC sheets, it has high durability, light in weight and fire proof. This consists of thin metal sheets which are galvanised and given the corrugation of bent shape for additional strength. These sheets are fixed on purlins with special screws.
6. Aluminium or PVC Sheets
Now-a-days Aluminium or PVC sheets similar to corrugated sheets are available which are light in weight, easy to handle and available in different colours.
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