What is the minimum end lap required when laying GRP sheets?

A minimum end lap of 150 mm is specified to ensure weather-tightness. (Clause 6.2.1)

How should I cut GRP sheets on site?

Use a fine-toothed handsaw or a power saw with a carbide or abrasive disc. The sheet should be well-supported on both sides of the cut line. (Clause 6.1)

What is the rule for side laps?

Side laps should be a minimum of one full corrugation and arranged to face away from the prevailing wind direction. (Clause 6.2.2)

Are special washers required for fasteners?

Yes, sealing washers, typically of bitumen or neoprene bonded to a metal washer, must be used with all fasteners to provide a watertight seal. (Clause 6.3.3)

IS 15224

: 2002

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

CurrentSpecializedCode of PracticeBIMArchitectural · Flooring, Wall Finishing and Roofing

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This code of practice outlines the methods for handling, storing, laying, and fixing translucent plastic sheets made from glass fibre reinforced polyester resin (GRP). It covers installation for roofing and side cladding, either as the primary covering or in conjunction with other roofing materials like steel or asbestos cement sheets, to ensure a durable and weather-tight installation.

Quick Reference Values

Minimum recommended end lap150 mm

Minimum recommended side lapOne full corrugation

Minimum recommended roof slope1 in 20 (approx. 3 degrees)

Oversize for pre-drilled fastener holes2 to 3 mm larger than fastener diameter

Maximum purlin spacing for general use1400 mm

Maximum unsupported overhang at eaves75 mm

Practical Notes

Always pre-drill holes for fasteners and make them 2-3mm oversized to accommodate thermal expansion, preventing stress cracks in the sheet.

Fasteners must be fixed through the crest (top) of the corrugation profile, never in the valley (bottom), to minimize the risk of water leakage.

Store sheets flat on a level surface, preferably indoors or under a cover, to protect them from distortion, discoloration, and physical damage before installation.