Code of practice for patent glazing
1983 Edition

IS 10439 (1983) suggests several glass types suitable for patent glazing including float glass, available in both clear and tinted varieties; toughened (tempered) glass which offers enhanced strength and safety especially in impact-prone areas; laminated glass which retains fragments upon breakage for added safety; and wired glass used where fire resistance is necessary. Typically, glass thickness ranges from 4 mm to 6 mm depending on panel dimensions and loads. For safety in occupied spaces, toughened or laminated glass is preferred. Selection should consider wind pressures, impact resistance, and thermal stresses as outlined in IS 875 and IS 2553.

Glazing bars are designed by considering the combined effects of wind pressure, the weight of glazing bars and glass, maintenance loads (converted to equivalent pressures), and snow loads. The required section modulus (Z) is calculated using the formula Z = (p × d² × s) / (8f), where p is the working pressure, d is the unsupported span between bars, s is the bar span, and f is the allowable proof stress (154 N/mm² for aluminium, 246 N/mm² for steel). Fixings should use corrosion-resistant screws or bolts, ensuring at least one fastening per purlin with minimum bearing lengths of 40 mm at the top and 50 mm at the bottom. Additionally, the lower end should be elevated on a washer to prevent condensation, with special fixings applied in high wind regions.

To minimize condensation on glazing, the standard advises maintaining a glazing pitch greater than 30° to promote runoff of condensate rather than dripping. Drainage should be provided at draught excluders to safely channel water. Limiting glazing depth by using multiple tiers or separate runs reduces droplet formation. Employing double glazing is beneficial, especially where interior environments are warm and humid with low glazing pitch. Insulating glazing bars by covering surfaces exposed to interior air and separating aluminium bars from steel structures with non-metallic materials helps reduce cold spots. Adequate ventilation is also essential to control humidity and further reduce condensation risk.

IS 10439 stipulates that the maximum size for a single glass pane in patent glazing should not exceed 2 meters in either length or width, effectively limiting panes to 2 m × 2 m. For greater glazing depths, the use of two glass panes separated by an intermediate muntin section is recommended. The muntin is usually fabricated from 0.45 mm thick aluminium sheet to enable secure capping at the edges, particularly for vertical glazing. For inclined glazing applications, lapped glazing is preferred over muntins to maintain structural integrity and ease of installation.

The standard emphasizes selecting materials for glazing bars and fittings that resist corrosion under expected environmental conditions. It advises against the proximity of dissimilar metals that could cause galvanic corrosion, specifically ensuring copper or its alloys are positioned so rainwater does not flow onto aluminium or zinc alloys. Aluminium use should be avoided in alkaline pollution environments. For airtight glazing, double cushioned glazing bars or similar designs are recommended to enhance sealing and durability. These guidelines ensure longevity and reduce corrosion-related failures in glazing assemblies.