SELECTION OF ROOF COVERING MATERIALS

The following factors require due consideration in selecting a roof covering for a building:

1. Climatic conditions of the locality: The climatic conditions have a marked influence on the performance and durability of roof coverings. Strong winds may damage the roof covering such as slates, tiles and AC sheets by blowing it off, if not properly fixed in position. Extreme temperature changes may cause the sheets to crack and the joints to leak, if not properly protected. Atmospheric effects of fog, salt air, smoke and other gases may result in corrosion of metal roofing if not protected by painting; clay tiles, slates, AC sheets and built-up roof coverings are unaffected by atmospheric action.
2. Slope of roof: The flatter the slope the greater would be the effect of rains, causing leakage in the roof. However, the steeper the slope the greater would be the effect of wind action, requiring heavier supports and more covering material. Thus, the slope of the roof influences both the strength and the economy of the roof and is decided by considering climatic conditions of the locality and the material of roof covering. Thatch, tiles and slate usually require steeper slopes to prevent water infiltration whereas corrugated sheets and concrete terraces require flatter slopes.
3. Nature of the building and of the roof deck: A roof covering must be in conformity with the nature of the building as well as of the roof deck. It is the roof deck to which all the types of roof covering are fastened. The decks are supported on principal supporting members such as girders, trusses and rigid frames. Sometimes the deck serves as a principal supporting member in shell roofs.
4. Initial cost: The initial cost of roofing material is not a definite value and depends upon the time and place and materials availability. For example, a roofing of slates or wood may be cheaper in hilly regions. In the cost analysis of roof covering, it should be noted that the cost of supporting structures and the deck should be accounted in the initial cost because the materials, which are cheap and heavier, may require a strong and costly supporting structure as in the case of slate roofing in hilly regions.
5. Maintenance cost: While considering the overall economy of the roof covering, the maintenance cost may become as important as the initial cost. Wood shingles and tiles need less maintenance and repairs than thatch roofing. Asbestos sheets and slates may be broken and require replacements occasionally. Galvanized iron sheets require only periodic painting to check its tendency to corrosion.
6. Durability: The durability or life is an important factor in assessing the economic value of roof coverings. The life of a roof covering is affected by its quality, its suitability for the purpose used, climatic conditions, workmanship in fixing and laying, degree of maintenance and many other factors. Under normal weather conditions, when all roof covering are laid in the best possible way, clay tiles, slates and galvanized iron (GI) sheets are said to have longer life.
7. Resistance to fire: The roof covering should offer sufficient resistance in the event of fire. From the fire resistance point of view, roof covering of slates, AC sheets, GI sheets, etc. are considered to be quite satisfactory, whereas thatch and shingles are unsatisfactory for this purpose.
8. Heat insulation: The roof covering should offer adequate insulation against heat so that the inside of rooms can be kept cool and comfortable for living. This is particularly important in tropical countries.
9. Weight of roofing material: The weight of roof covering affects the design, weight and the cost of roof deck as well as supporting structure and frame work. Heavier roof covering requires stronger supporting structure, which adds to the cost.
10. Appearance: It is an important factor for residential and other public buildings but is of less significance in the case of industrial buildings. The appearance depends upon the architectural style of the building and the class of occupancy.