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")
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.
Layout of Roofing
- The sheets should be laid on Purlins and other roof members as indicated in the drawing.
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
- Bitumen and Steel Washers
- Frame /‘Purlins’
- Ridge and Hip Cap
- Metal Valleys