Laying of Plastic Translucent Sheets Made from Thermosetting Polyester Resin (Glass Fibre Reinforced) Alone or in Conjunction with Asbestos Cement Sheets/Steel Sheets/Aluminium Sheets - Code of Practice
2002 Edition

Support centres should adhere to maximum spacing limits based on sheet profile depth, with deflection under wind gusts limited to span divided by 15 (not exceeding 100 mm) and under imposed loads to span divided by 30 (not exceeding 50 mm) to prevent damage. Fixing involves one corrugation overlap at side laps, secured with stitch bolts spaced at 400 mm for roofs pitched above 10°, or 300 mm for lower pitches. End laps require a minimum length of 150 mm for pitches of 18° or more, increased for shallower slopes or exposed locations. Holes for purlin fixing must be at least 100 mm from sheet edges, and fixing hardware should include bituminous felt washers, galvanized iron nuts, and appropriate bolts or screws such as J-type hook bolts. Overhang at eaves should not exceed 230 mm, and mastic sealant is recommended for laps on roofs with pitches of 18° or less.

When these sheets are installed together in chequerboard or eaves-to-ridge patterns, plastic translucent sheets must be uniformly distributed across the roof area at consistent pitch to ensure balanced daylight transmission. Use molded plastic translucent accessories for roofs fully laid with plastic sheets, while mixed roofs should apply accessories conforming to the respective codes for asbestos cement, steel, or aluminium sheets, ensuring all fittings match sheet profiles accurately. Corrugations must align continuously and straight to prevent leakage, and laps and fastening should comply with respective material codes.

Fixings should include bolts and screws with a minimum diameter of 8 mm, such as hook, cranked, U-shaped, J-shaped, square bend hook bolts, and L-bolts meeting IS 730 standards. Galvanized iron washers of flat, curved, or diamond patterns paired with bituminous felt washers (round or diamond-shaped) are essential to ensure watertight fastening. Nuts or screw heads must bear on galvanized washers embedded on bituminous felt washers, tightened just enough to seat the felt without restricting roof movement. Plastic roofing accessories like corner rolls and barge boards should be fastened using the same bolts as the sheets to maintain uniformity and secure installation.

Mitre cutting involves angled trimming of sheet edges where four sheets overlap, typically cutting from a point at least 15 cm up the vertical edge to 4.5 cm along the horizontal edge, using a saw with 6 to 8 teeth per centimeter for clean cuts. This ensures a tight fit preventing water ingress. For plastic translucent sheets, two of the overlapping sheets must be mitred as per the code’s diagrammatic guidance. Flashing, such as plastic apron flashing at top edges and metal or felt covers for masonry walls, should be applied over overlaps. Flashings should cover at least one full corrugation and be minimum 150 mm wide. Sheet edges should maintain a 125 mm clearance from wall surfaces where corrugations run into the wall face.

Regular cleaning with warm water combined with mild detergent is recommended, using gentle brushing to remove persistent stains. For tar or grease contamination, solvents like white spirit or acetone may be applied cautiously in well-ventilated areas. To uphold the sheets’ appearance, a clear, water-white air-drying lacquer can be applied after cleaning and drying. Sheets should be protected from wind damage and covered with waterproof sheeting if stored outdoors to prevent moisture accumulation and discoloration from solar exposure. Safety protocols for handling associated materials such as asbestos cement, steel, or aluminium sheets must also be observed to ensure overall maintenance safety.