Laying of Asbestos Cement Sheets Code of practice, Part II: Semi-Corrugated Sheets
1999 Edition

The fixing hardware for semi-corrugated asbestos cement sheets should comply with IS 730 to ensure compatibility and quality. Ridge cappings are secured to ridge purlins using the same bolts as the roofing sheets. Accessories such as barge boards, eaves filler pieces, and apron flashings are attached either directly to the structural framework or fastened to the sheeting using seam bolts. At eaves, verges, and gable ends, asbestos cement accessories close off corrugations, with barge boards or corner rolls recommended at gable ends. Alternatively, verge sheeting may be bedded in mortar if supported by masonry walls. Proper accessory selection and installation techniques are vital for weather resistance and durability.

Expansion joints are essential for accommodating thermal and structural movements in large asbestos cement roofs. According to IS 3007 Part 2, these joints should be spaced no more than 35 meters apart. The minimum end lap for expansion joints is 150 mm, consistent with standard roofing sheets. If the expansion joint occurs between purlins, lap areas must be securely stitched with roofing bolts to maintain structural stability. Fixing accessories like bituminous felt washers and J-type hook bolts are specified for these joints to ensure proper sealing and durability.

To reduce asbestos dust exposure during installation, sheets must be stored in shaded, ventilated locations to avoid thermal stress and cracking. Water sprinkling is recommended in hot, dry conditions to suppress dust. Cutting and drilling should be performed with tools specified in the standard that minimize dust, preferably using wet cutting or extraction systems. Dry sweeping is discouraged; instead, wet cleaning or vacuuming should be used. Workers must wear appropriate respiratory protection such as N95 masks and limit exposure duration. Strict adherence to IS 11769 Part 1 guidelines is necessary to safeguard health during handling.

The preferred minimum roof slope for semi-corrugated asbestos cement sheets is 18 degrees. If a roof pitch below this is unavoidable, end laps must be increased beyond the standard 150 mm and joints sealed according to manufacturer or engineering guidelines. Side laps should involve one corrugation overlapped by the adjacent sheet’s corrugation and be positioned to minimize exposure to prevailing winds. The free overhang at the eaves should not exceed 300 mm to maintain watertightness and roof integrity.

Gutters and rainwater pipes should be installed to effectively channel water away from the roof. Half-round gutters are preferred where sufficient valley space exists; otherwise, flat gutters plastered and covered with lead sheets are acceptable. Purlins must be positioned to support the roof overhang and ensure proper gutter alignment. All materials including gutters, downpipes, brackets, and fixings must be on site before installation. Installation must follow relevant codes, ensuring gutters slope correctly for drainage and that pipes are adequately supported for durability and functionality.