Code of Practice for Glazing in Buildings
1988 Edition

To determine the minimum glass thickness for vertically positioned windows fixed on all four edges under wind pressure: first, estimate the maximum wind load using data from IS 875, considering both inward and outward pressures and adjusting for building height and exposure. Next, compute the Glass Factor (GF) as the ratio of the glass pane’s area to its perimeter, using the formula GF = (A × B) / [2(A + B)], where A and B are pane dimensions in meters. Then, refer to the thickness nomogram provided in IS 3548 to find the required minimum thickness based on design pressure and GF, considering the modulus of rupture values for sheet and plate glass. Typical thickness ranges from 4-5 mm for lower pressures (~500 N/m²) to 6-10 mm for higher pressures (~1500-2000 N/m²), depending on size. The approximate weight can be calculated as 2.6 times the thickness in millimeters.

For safe glazing, rebate depths generally should be at least 8 mm for normal panes, 6 mm for smaller panes, and 10 mm for large windows such as shop fronts, with the bottom rebate being at least 12 mm. Double or multiple glazed sealed units typically require a rebate depth of 16 mm unless otherwise specified by the manufacturer. Rebate widths must accommodate the glass, back putty, and front putty fillet with a minimum 1.5 mm clearance at both front and back to prevent stress. The back putty thickness should be at least 1.5 mm. Glass edge clearances should be maintained to allow for compound bedding and thermal movement. The glass should be secured with springs or spring clips spaced no more than 450 mm apart. These dimensions prevent stress concentrations and ensure water tightness.

The standard specifies several types of glazing compounds: traditional putty conforming to IS 419-1967, and polysulphide-based sealants including one-part (IS 11433 Part 1-1985) and two-part (IS 12118 Part 1-1987) variants, which provide elastic and durable sealing. Non-setting compounds are advised for heat-absorbing or colored glass to accommodate expansion, and such compounds should be paintable and resistant to alkali when used with materials like concrete or stone. Fixing involves applying a back putty layer at least 1.5 mm thick between glass and rebate, squeezing out excess compound and stripping it at an angle to avoid water accumulation. Glass is held with springs or clips spaced not more than 450 mm apart, and the front compound is formed into a triangular fillet stopping 1.5 mm short of the sight line for sealing with paint.

Double glazing, as per the code, involves two glass panes separated by a static air space to enhance thermal and acoustic insulation. It can be realized by two independent frames in a single opening, a single frame with two coupled sashes each glazed separately, a single frame with two glasses glazed on site, a single frame with a second glass attached via clips, or factory-made hermetically sealed double glazing units. Installation guidelines emphasize providing access for cavity cleaning when using separate frames, using separate or wide rebates with spacing beads for coupled sashes, ensuring easy detachment for clipped-on second glass systems, and following manufacturer specifications for sealed units. Proper sealing and ventilation, including small breathing vents, are essential to prevent moisture and preserve insulation performance.

Routine cleaning should be performed using warm water combined with soap or mild detergents, rinsing thoroughly with clean water. Transparent glass is best cleaned with a soft cloth or wash leather, while textured or broken surface glass requires a stiff plastic or bristle brush. For stubborn dirt, polishing with whiting in water or methylated spirits is effective. Specific solvents may be used cautiously for stains—petrol or benzene for tar, turpentine for uncured paint, and paraffin for grease—but residues must be cleaned promptly to avoid damage or fire hazards. Plaster or dried paint should be carefully removed with a thin razor blade before hardening. Special textured glasses may need professional cleaning. Regular maintenance, including painting glazing compounds and preventing corrosion or timber warping, helps avoid glass breakage and prolongs service life.