Laying of Asbestos Cement Sheets - Code of Practice, Part 1: Corrugated Sheets
1999 Edition

The suggested fixing components for corrugated asbestos cement sheets include roofing bolts as the primary method for securing sheets and related accessories such as barge boards, corner rolls, apron flashings, and ridge cappings. Ridge cappings must be fastened to ridge purlins using the same bolts as those securing the sheets, while barge boards, eaves fillers, and apron flashings can be attached either to the supporting structure or directly to the sheeting using roofing bolts. Overhanging verges require support from purlins spanning the full sheet width with adequate fixing to resist uplift caused by wind. Eaves filler pieces are used to seal corrugations at eaves or above glazing and can alternatively be bedded in mortar on masonry walls. Proper installation of these accessories ensures robustness and wind resistance of the roofing system.

Asbestos cement sheets should be stored in a sheltered location close to the area of installation to reduce handling. Stacks must be uniform and organized by size and type, avoiding the mixing of damaged and undamaged sheets. When sheets are stored outdoors for extended periods, they should be shielded from direct sunlight to prevent thermal stress-induced cracking, using shading solutions such as tarpaulins or temporary covers. Gentle handling is critical to prevent damage, and any damaged sheets should be promptly removed and salvaged. These measures help maintain the sheets’ integrity and durability during storage.

For correct installation, side laps on corrugated asbestos cement sheets should be equal to half the width of one corrugation and positioned on the side protected from prevailing winds. The end lap dimension depends on the roof pitch: a minimum of 150 mm for roofs pitched at 18 degrees or greater, and a larger overlap is recommended for roofs with less than 18 degrees pitch or exposed conditions, subject to manufacturer guidance. All laps must be supported adequately. Sheets must be installed with the smooth side facing upwards, corrugations running in straight lines, and mitred corners provided at four-sheet overlaps for a snug fit. Additionally, the maximum free overhang at eaves is 300 mm for 6 mm thick sheets and 150 mm for 4 mm thick sheets, measured to the center of the fixing hole.

Ridge capping is designed to fit the corrugation profile of asbestos cement sheets that have sidelaps equal to half a corrugation, with a corrugation pitch of 134 mm at the side lap. Installation begins at the left-hand verge, placing the small roll wing inner so its first valley on the right aligns with the valley of the sheet sidelap. Large roll wings are positioned with their first valley on the left fitting into the corresponding valley of the sheet sidelap. Ridge capping is secured to ridge purlins using the same bolts as the sheets wherever feasible or by roofing bolts fastening each wing to the sheets. The capping should initially extend beyond the verge and then be trimmed to size. Sheets on either side of the ridge are laid in opposite directions to ensure corrugation alignment. Utilizing a template during fixing facilitates accurate and stress-free fitting of the ridge capping.

During installation, asbestos cement sheets, which contain a small percentage of asbestos, should be handled with care. Limited cutting, such as mitre cutting, must be performed outdoors to minimize dust generation. If dust levels are a concern, reference IS 11769 (Part 1) or consult the manufacturer for safe handling practices. Workers should only walk on planks or ladders positioned over the sheets to avoid damage and safety hazards; stepping directly on sheets is prohibited and safety signage must be displayed to enforce this. Proper accessories should be used and workmanship maintained to ensure durability and safety. For sheet lengths exceeding 45 meters, expansion joints aligned with structural joints must be provided to prevent stress and cracking. These precautions collectively ensure safe and effective asbestos cement roofing installation.