Asbestos cement sheet roofing should consist of either corrugated sheets or semi corrugated sheets as specified. The sheet should be of approved quality and shall confirm IS: 459. The sheet is free from cracks, chipped edges or corners and other damages. The slope of the roof is not less than 1 to 5. Normal slope adopted usually is 1 to 3.
Holy place with ACC sheet roof over it
(This Picture is Contributed by "Gungya")
Layout of Roofing
- The sheets should be laid on Purlins and other roof members as indicated in the drawing.
- The lines of corrugations are truly parallel to the sides of the area to be covered. Purlins spacing should not exceed 1.65 meters.
- Each sheet should be laid with a minimum lap of 15 cm at the ends.
- For corrugated sheets the side lap should be half a corrugation whereas for semi corrugated type it should be one corrugation.
- The sheets should be laid on smooth side.
- The sheets should be fixed to Purlins by means of galvanized hook bolts or crank bolts of approved type and size.
- The diameter of bolts should not be less than 8 mm.
- The holes for bolts are drilled (not punched) in the ridge of corrugations while sheets are on the ground.
- The holes are not drilled in valleys.
- Hole-diameter is 3 mm greater than bolt diameter.
- Each galvanized bolt should have a bitumen washer and a galvanized washer placed over sheet before the nut is screwed down from above.
- The nut should be tightened to make the joints leak proof.
- Wind ties must be provided on ACC sheet roofing to save it from disaster etc.
- Proper ridges should be provided where it is required according to the site condition.
- For drainage of rainy water through pipes proper valley gutters should provided in case of multi span sheet roofing.
Common Defects during erection of A.C.C. Sheet Roofing
- Sheets are punched rather than drilled for making holes into bolts.
- Wrong holes are made at some places and are not closed in later.
- Lap length of sheet is not proper.
- Cracked sheets are used.
- Hooks’ bolts are loose.
- Length of hooks’ bolts is not as per specification.
- Bitumen and G.I. limpet washers used are of sub standard.
- Bitumen washers are not provided at some places.
Advantages of A.C.C. Roofing
- It is economical.
- It covers more space with less intermediate supports.
- It remains cool as it observes less heat.
- It takes less time for fixing as compared to RCC roof.
Disadvantage of A.C.C. Roofing
- Problem of breakage and leakage
- It can not be used for second storey.
- This is not so safe against disaster.
Raw Materials used for A.C.C. Roofing
- ACC sheet
- Hook
- Bolts
- Bitumen and Steel Washers
- Nuts
- Frame /‘Purlins’
- Ridge and Hip Cap
- Metal Valleys