ROOFING MATERIALS
ROOF :A roof is the uppermost part of a building, provided as a structural covering, to protect the building from rain, sun, wind, etc. Roof protects the building from the dam- ages starting from the top.
Requirements of Good Roof
The following requirements are to be satisfied by a well planned roof:
i. It should be durable against the adverse effects of wind, sun, rain etc.
ii. It should give good insulation against heat and sound.
iii. It should be structurally sound and stable.
iv. It should permit good drainage.
v. It should have good water-proofing arrangement.
vi. It should be fire resistant.
ROOF COVERING MATERIALS
1. Thatches
2. Wooden shingles
3. Tiles
4. A.C. sheets
5. G.I. sheets
6. Light weight roofing materials
7. Poly vinyl chloride sheets
8. Reinforced cement concrete
9. Galvalume sheets
Points to be considered during the selec- tion of roofing
MATERIALS
1. Climate of the locality
2. Slope of the roof
3. Type of the building
4. Durability
5.Construction and maintenance cost of the buliding
6. Resistance to fire and heat
7. Weight of the roofing materials
8. Appearance and beauty of materials
Types of covering sheets for Pitched Roof
1. Asbestos cement sheets
2. Light roofing sheets
3. Galvanized iron sheets
4. Galvalume Sheets
1 ASBESTOS CEMENT SHEETS: They are manu- factured by mixing the cement with about 15% of asbestos fibre. These fibres are so soft like silk. The corru- gations help to increase the strength and rigidity and they permit easy flow of rain water.
TYPES OF A.C SHEETS
i. Trafford sheet
ii. Corrugated sheet
1. TRAFFORD SHEET Each trafford sheet con sists of four deep corrugations alternating with flat portions. The thickness of these sheets is 6 mm. They are available with a breadth of 1.02 in and lengths of 2.5 m, 3 m, 3.5 m and 4 m.
ii. CORRUGATED SHEET: These sheets are pre- pared by pressing plates between rollers. These sheets are manufactured with series of parallel depression (corrugations) from one end to the other. These sheets are more resistant to fire. These sheeta produce noise when rain water falls on them. Crank bolts and ‘J’ hooka are used to fix these sheets with the purlina. To avoid the leak- age of water bituminous washers are used. There are 7.5 corrugations in this sheet. The upper and lower corrugations are equal. The thickness of these sheets is 6 mm. They are available with a breadth of 1.05 m and lengths of 2.5 m, 3 m, 3.5 m and 4 m.
USES OF A.C. SHEET
i. A.C. sheets are fairly cheap and not easily affect- ed by fire.
ii. They need not be painted.
iii. It is not affected by insects.
iv. It is used in industries, large buildings and work- shops.
CHARACTERISTICS OF A.C. SHEET
● They are sound proof.
●They are not affected by acids and alka- lis.
● They are not good conductor of heat.
● Less maintenance cost.
● They are used for decorative purposes.
1.A.C. RIDGE PIECE COVER
To avoid water entering into the roof the cover pieces laid at the top junction of the two sloped A.C. sheets are known as A.C. ridge covers.
2. LIGHT ROOFING SHEETS: These roof coverings are manufactured by inserting tar felt inbetween the two asbestos clothes with corrugations. The thick- ness of these sheets is 3 mm. They are available in a breadth of 1 m and lengths of 2 m, 2.5 m and 3 m. They are painted with aluminium paint on both sides. They are easily bendable. They are easy to be cut and nailed. These sheets are cheap in cost but has less strength. This type of roof covering is suit- able for cattle sheds and nutrition centres.
TYPES OF LIGHT ROOFING SHEETS
1. Tar sheet
2. Plastic sheet
3. Poly vinyl chloride sheet
3. GALVANIZED IRON SHEETS: These sheets are pre- pared by pressing wrought iron plates between rollers. They are galvanized with a zinc coat to avoid rusting due to climatic change. They are strong due to corruga- tions. They are also manufactured as plain sheets.
ADVANTAGES OF GALVANISED IRON SHEET
i. They need not be painted, so cost reduces.
ii. As it is less in weight handling is easier.
iii. Low conductor of heat.
iv. Not easily corrodible.
Modern Roofing Sheets
1. CORRUGATED ALUMINIUM SHEETS: Aluminium is a light weight metal and does not corrode like steel. The thickness of corrugated aluminium sheets vary from 0.5 to 0.8mm. They require no mainte- nance and has also a good resale value. The only dis- advantage is that they are more expensive.
2. PVC ROOFING SHEETS: Rigid PVC corrugated sheets are transparent with a light transmission of not less than 70 to 80 percent. Since these sheets do not perform well with direct exposure to sunlight and are also not fire proof, they are mainly used in tem- porary constructions, car parks etc. where a very light roofing of pleasing appearance is required.
3. GLASS FIBRE REINFORCED PLASTIC SHEETS: Corrugated glass fibre reinforced plastic sheets with different profiles and light transmissions are used as light roofing materials. Unlike GI and aluminium sheets, these sheets have little resale value.
4. BITUMINOUS SHEETS: Light roofing made of bitumen and paper pulp is generally used for cover- ing of temporary sheds. They are cheap but their life is very short (3 to 5 years). They do not have resale value.
5. RED MUD CORRUGATED ROOFING SHEETS: Red mud is obtained from waste materials derived in aluminium industry. It is combined with polymers to form corrugated roofing sheets. They are cheap and more durable. Since red mud corrugated roofing sheets are very flexible, they are extensively used as a light roofing material for temporary construction
6. GALVALUME SHEET: Galvalume sheets are com- mercially available light steel roofing sheets made up of lowtensile steel or mild steel. These sheets are 4 times more corrosive resistant than G.I. sheets and are one of the most economical and durable material. The versatility, ease of use, aesthetics and long term performance of the material makes it best preferred material for roofing
