Code of Practice for Glazing in Buildings

IS 3548: Scope - Key Specifications & Tables

Scope (Clause 2.1):
Defines terms related to glass types, thickness, and applications for building use.

Key Points from IS 3548 for Glazing:

• Glass Types & Thickness:
  Clear, heat absorbing, figured, wire-cast, double glazing (two 3 mm clear glasses).

• Heat Insulation & Light Transmission (Clause 5.5):

  • Double/multiple glazing improves insulation; spacing critical (optimal ~10 mm vertical, >20 mm horizontal).
  • Frame thermal conductivity affects overall insulation.

Table 1: Diffuse Light Transmittance & Heat/Light Ratio

*Note: Heat/light ratio for double glazing depends on spacing.

Ordering & Planning Info (Clauses 3.1 & 3.2):

• Specify type, thickness, quality, color, pattern.
• Provide measurement mode (height first), tight size, and allowances.
• For shaped/bent glass, supply templates or drawings indicating concave/convex sides.
• Specify alignment for patterned, wired, leaded or copper lights.

Summary Diagram: Heat Insulation vs Spacing for Double Glazing

graph LR
A[Spacing < 3 mm] --> B[~50% Max Insulation]
B --> C[Spacing ~10 mm]
C --> D[Max Insulation]
D --> E[Spacing > 10 mm]
E --> F[Little Further Improvement]

This concise info aids in specifying glass for thermal and light performance per IS

IS 3548: Key Definitions & Specifications

1. Definitions (Clause 2.1)

• The standard defines terms relevant to glass specifications and installation.
• Example: Back Clearance (Clause 2.1.2) refers to the gap behind the glass for fitting and movement (see Fig. 1A in the standard).

2. Glass Ordering Information (Clause 3.2)

When ordering glass, specify:

• Type, quality, thickness, and substance
• Size dimensions: Height first; specify measurement mode (tight size, pane size)
• For shaped or special glass (bevelled, double glazing, leaded lights), provide both tight and sight sizes.
• For patterned or wired glass, specify alignment requirements.
• For bent glass, provide templates or drawings indicating concave/convex sides and curves.

3. Light Transmission & Heat Insulation (Clause 5.5, Table 1)

• Note: Heat insulation improves with double/multiple glazing; spacing ~10 mm optimal for vertical glazing.

Summary Diagram: Glass Ordering Info Flow

flowchart TD
    A[Specify Glass Type & Quality] --> B[Specify Dimensions (Height first)]
    B --> C{Special Glass?}
    C -->|Yes| D[Provide Tight & Sight Sizes]
    C -->|No| E[Standard Sizes]
    D --> F{Bent Glass?}
    F -->|Yes| G[Provide Template or Drawing]
    F -->|No| H[Proceed with Order]
    E --> H
    G --> H

Key Information for Ordering Glass (IS 3548: Clause 3.2 & 3.1)

When ordering glass, provide the following details to the supplier:

• Type, quality, thickness, and substance of glass (e.g., clear, wired, patterned).
• Size specifications:
  • Height given first.
  • Mode of measurement (tight size, glass pane size).
  • Allowances for coloured glass if applicable.
• Template details for shaped glasses (specify face side).
• For bevelled, decorated, double glazing, leaded, copper lights, louvre ventilators: provide both tight and sight sizes.
• For patterned or decorated glass requiring alignment, provide dimensional sketches.
• For wired glass alignment between panes, specify alignment direction.
• For bent glass, provide:
  • Rigid template for one-way bends (mark concave/convex).
  • Drawings with radius for arc bends.
  • Rigid mould for bends both ways.

Additional Planning Info (Clause 3.1):

• Glass type with colour, pattern, ornamentation.
• Techniques and other materials to be used.

Light Transmission & Heat Insulation (Clause 5.5, Table 1)

* Heat/light ratio for double glazing depends on spacing (optimal ~10 mm).

Standards for Glass (Clause 4.1)

• Sheet glass: IS 2835-1977
• Safety glass: IS 2553-1971
• Wired and figured glass: Refer respective IS codes.

flowchart TD
    A

IS 3548: Glass Types & Applicable Indian Standards

Glass Types & Relevant IS Codes (Clause 4.1)

• Sheet Glass: IS 2835-1977 (Flat transparent sheet glass)
• Safety Glass: IS 2553-1971 (Tempered, toughened, laminated)
• Wired & Figured Glass: Refer IS 3548 (specific clause)

Glazing Compounds (Clause 4.2)

• Putty: IS 419-1967 (for window frames)
• Polysulphide Sealants:
  • One-part gun-grade: IS 11433 (Part 1)-1985
  • Two-part sealant: IS 12118 (Part 1)-1987

Key Notes:

• Non-setting compounds are recommended for heat-absorbing/colour glass due to expansion.
• Alkali resistance is important for compounds used with concrete, stone, brick, or asbestos cement.
• Compounds should be paintable if required.

Summary Table:

flowchart TD
    A[Glass Types] --> B[Sheet Glass (IS 2835)]
    A --> C[Safety Glass (IS 2553)]
    A --> D[Wired & Figured Glass]
    E[Glazing Compounds] --> F[Putty (IS 419)]
    E --> G[Polysulphide Sealants]
    G --> H[One-part (IS 11433)]
    G --> I[Two-part (IS 12118)]

This ensures safe, durable glazing conforming to Indian standards for building construction.

Selection of Glass Thickness as per IS 3548 - Key Points

1. Determining Design Wind Pressure:

• Use maximum wind load averaged over 1-minute or preferably 3-second period.
• Account for inward and outward pressures.
• Adjust for building height and shielding (IS 875-1964).

2. Glass Factor (GF):
[ GF = \frac{\text{Area of glass pane (m}^2)}{\text{Perimeter (m)}} = \frac{A \times B}{2(A + B)} ] where A and B are pane dimensions in meters.

3. Minimum Thickness:

• Use Fig. 2 nomogram (from IS 3548) relating design pressure and glass factor to find thickness.
• Modulus of rupture:
  • Sheet glass: 38 N/mm²
  • Plate glass: 19 N/mm² (adjusted for variability)

4. Weight of Glass: [ \text{Weight (kg/m}^2) \approx 2.6 \times \text{Thickness (mm)} ]

Table: Light Transmission & Heat/Light Ratio (Clause 5.5)

Summary Diagram of Thickness Selection Process

flowchart TD
    A[Determine Wind Load] --> B[Calculate Design Pressure]
    B --> C[Calculate Glass Factor (Area/Perimeter)]
    C --> D[Use Nomogram (Fig. 2) to find Thickness]
    D --> E[Check Weight and Order Specifications]

Note: For ordering, specify type

IS 3548: Glazing Methods & Installation Details

Key Specifications & Formulas

1. Heat Insulation & Light Transmission (Clause 5.5)

• Double/Multiple Glazing improves heat & sound insulation.
• Optimal spacing for vertical glazing: ~10 mm (max insulation).
• Minimum effective spacing: 3 mm (~50% max insulation).
• For inclined/horizontal glazing: spacing > 20 mm may be advantageous.
• Frame thermal conductivity affects overall insulation negatively.

* Heat/Light ratio for double glazing varies with spacing.

2. Glazing Methods

• Compound Glazing (Clause 6.4):
  Suitable for panes where (height + width) ≤ max dimension in Fig.1 (exposure grading).

• Bead Glazing (Clause 6.5):
  Used when (height + width) > max dimension in Fig.1, especially for:

  • Unpainted hardwood frames
  • Framed shopfronts
  • Double/multiple glazing units
  • Situations with non-setting compound prone to disturbance

Summary Diagram of Glazing Selection

flowchart TD
    A[Pane Size: Height + Width] -->|≤ Max from Fig.1| B[Use Compound Glazing]
    A -->|> Max from Fig.1| C[Use Bead Glazing]
    C --> D{Frame Type}
    D -->|Unpainted Hardwood| E[Bead Glazing Required]
    D -->|Others| F[Evaluate

IS 3548: Size for Glass and Clearances

Key Specifications (Clause 6.1 & 5.4)

• Clearance between glass edge and frame:

  • For glass with longer dimension < 750 mm: ≥ 3 mm clearance all around
  • For longer dimension > 750 mm: ≥ 5 mm clearance all around

• Maximum cover for safe glazing (except toughened glass):
  ≤ 10 mm to avoid edge cracking due to thermal gradients.

• Glazing compound:
  Use non-setting compound; treat rebates/grooves with sealer.

Thermal Expansion & Contraction (Clause 5.4)

• Special care for heat absorbing or painted glass (especially black).
• Clearance accommodates expansion/contraction due to temperature changes.

Double Glazing Heat Insulation (Clause 5.5 & Table 1)

*Note: Double glazing spacing optimum ~10 mm for vertical glazing; 3 mm spacing gives ~50% max insulation.

Summary Formula for Glass Size:

[ \text{Glass size} = \text{Frame opening size} - 2 \times \text{Clearance} ]

Where clearance = 3 mm or 5 mm depending on dimension.

flowchart LR
    A[Frame Opening Size] --> B[Subtract 2 × Clearance]
    B --> C[Glass Size]
    C --> D[Install Glass with Non-setting Compound]

This ensures safe installation with allowance for thermal movement and prevents edge damage.

IS 3548 Key Points on Glazing with Compound

1. Maximum Pane Size (Clause 6.4)

• Suitable for panes where height + width ≤ maximum size shown in Fig. 1 (exposure grading dependent).

2. Fixing Compound (Clause 2.1.10)

• Compound: adhesive material applied by hand/knife/trowel or pre-formed strip.
• Adheres to various surfaces, used for securing glass.

3. Glazing with Compound into Rebates (Clause 6.6)

• Apply compound to rebate to form a back putty thickness ≥ 1.5 mm between glass and rebate.
• Surplus compound squeezed out and stripped at an angle (Fig. 1B) to prevent water accumulation.
• Glass secured by springs/clips spaced ≤ 450 mm around the pane perimeter.
• Front compound forms a triangular fillet, stopping 1.5 mm short of sight line for paint sealing.

4. Thermal & Light Properties (Table 1, Clause 5.5)

*Heat/light ratio slightly lower for double glazing due to air gap insulation.

Summary Diagram of Glazing with Compound (Fig. 1B)

flowchart LR
    A[Rebate] -->|Apply compound| B[Back putty ≥ 1.5 mm]
    B -->|Press glass| C[Glass pane]
    C -->|Surplus compound squeezed out| D[Compound fillet stripped at angle]
    D -->|Secure with springs/clips ≤ 450 mm| E[

IS 3548: Use of Beads and Fixing Components — Key Points

Fixing of Beads (Clause 6.8.3)

• Wooden frames: Use panel pins or screws.
• Metal frames: Fix as per frame design.
• Quantity: Adequate fixings to prevent bead flexing or movement.

Glazing with Beads (Clause 6.5)

• Applicable when pane dimensions exceed limits in Fig.1 (unpainted hardwood frames).
• Recommended for double/multiple glazing units.
• Use where non-setting compound is prone to disturbance.

Glazing with Beads & Compound (Clause 6.8)

• Apply back putty compound to rebate: minimum 1.5 mm thickness after glass is pressed.
• Compound surplus squeezed out above rebate; strip at an angle (not undercut) to avoid water accumulation.
• Beads bedded with compound against glass; wooden beads also bedded against rebate.

Additional Specifications (Clause 6.8.1)

• Avoid voids between glass and bead.
• Hollow beads are undesirable outdoors unless fully filled.

Summary Table:

flowchart TD
    A[Apply Compound to Rebate] --> B[Press Glass into Rebate]
    B --> C[Back Putty ≥ 1.5 mm Remains]
    C --> D[Fix Beads with Pins/Screws]
    D --> E[Beads Bedded with Compound]
    E --> F[Strip Surplus Compound at Angle]
    F --> G[Prevent Water Accumulation]

This ensures secure, weatherproof glazing with proper bead fixation per IS 3548.

IS 3548: Glazing Multiple Panes in One Frame - Key Points

1. Heat Insulation & Spacing (Clause 5.5)

• Optimal spacing for vertical glazing: ~10 mm (max insulation).
• Spacing as low as 3 mm provides ~50% max insulation.
• For inclined/horizontal glazing, spacing >20 mm may be beneficial.
• Frame thermal conductivity affects overall insulation (avoid conductive frames).

2. Diffuse Light Transmittance & Heat/Light Ratio (Table 1)

3. Types of Multiple Glazing (Clause 6.9)

• Two separate frames: Best for sound insulation; access needed for cavity cleaning.
• One frame with two sashes: Separate rebates or wide rebate with spacing beads; easier pane replacement.
• One frame with clip-on second glass: Easy detachment; suitable for retrofitting.
• Factory-made sealed units: No inner cleaning issues; follow manufacturer's rebate & glazing compound specs.

4. Factory-made Units Installation (Clause 6.11)

• Specify tight size and sight size.
• Provide edge clearance per manufacturer.
• Position blocks ~¼ length from ends; block thickness ≥ unit thickness.
• Use non-setting glazing compound (~1 mm thickness).
• Seal absorbent rebates; use solid glazing beads (no hollow).
• Use front/back distance pieces if pressure risk exists.

Summary Diagram: Multiple Glazing Types

graph TD
    A[Multiple Glazing Systems] --> B[Two Separate Frames]
    A --> C

IS 3548 Key Points on Factory-made Double/Multiple Sealed Units

1. Specifications (Clause 6.11)

• Specify tight size and sight size (not glazing size).
• Edge clearance must follow manufacturer’s recommendations.
• Position units approx. 1/4 length from each end in compound.
• Block width ≥ thickness of sealed units; glazing compound thickness ≈ 1 mm.
• Use non-setting glazing compound with good adhesion; treat absorbent rebates with sealer.
• Always use glazing beads (avoid hollow beads).
• Use front and back distance pieces where pressure might dislodge glazing.

2. Thermal & Light Properties (Clause 5.5, Table 1)

*Heat insulation improves with spacing up to ~10 mm for vertical glazing; 3 mm spacing yields ~50% max insulation.

3. Double Glazing Types (Clause 2.1.13.1 & 6.9)

• Factory-made sealed units provide hermetic seal, prevent cleaning issues inside cavity.
• Other types include two separate frames, coupled sashes, or clipped-on second glass.

Summary Diagram of Sealed Unit Positioning:

flowchart LR
    A[Opening] --> B[Position sealed unit]
    B --> C[Place blocks at 1/4 length from ends]
    C --> D[Use glazing compound (1 mm thickness)]
    D --> E[Insert glazing beads (solid, not hollow)]
    E --> F[Use distance pieces if pressure risk]

This ensures proper sealing, thermal performance

IS 3548 - Louvered Glazing Key Points

1. Types of Louvered Glazing

• Horizontal Louvered Glazing (Clauses 6.12.1, 2.1.13.3):

  • Glass strips with rounded edges inserted inside grooves on the frame.
  • Grooves are angular, preferably at 45°.
  • Each groove overlaps the one below by at least 20 mm for weather tightness.
  • Strips are placed one above the other, sloping outward.

• Vertical Louvered Glazing (Clauses 6.12.2, 2.1.13.4):

  • Glass strips placed angularly and vertically side by side at an angle.
  • Inserted similarly as horizontal glazing but oriented vertically.

2. Groove and Glass Strip Specifications

• Groove angle: ~45°
• Overlap: ≥ 20 mm
• Glass strip edges: Rounded to avoid stress concentration.

3. Functional Notes

• Overlapping ensures rainwater runoff and air ventilation.
• Angular placement helps in shade and light control.

Diagram: Horizontal Louvered Glazing Groove & Glass Strip

flowchart LR
    subgraph Frame
    G[Groove @ 45° angle]
    end
    Glass[Glass strip with rounded edges]
    G --> Glass
    Glass -->|Overlap ≥ 20 mm| Glass2[Next glass strip below]

Summary:
Use rounded glass strips inserted into 45° grooves with at least 20 mm overlap for effective horizontal louvered glazing. Vertical glazing follows similar angular placement but arranged vertically side by side.

IS 3548: Cleaning & Maintenance of Glazing — Key Points

Cleaning (Clause 6.13.1)

• Routine cleaning: Use warm water + soap or mild detergent; rinse with clean water.
• Tools:
  • Transparent glass: cloth or wash leather.
  • Textured/broken surface glass: stiff plastic/bristle brush.
• Stubborn dirt: Polish with whiting in water or methylated spirits.
• Solvents: Petrol/benzene (tar), turpentine (wet paint), paraffin (grease); clean off after use, beware fire risk.
• Plaster/mortar or dried paint: Remove carefully with a thin razor blade; avoid excessive force.

Maintenance (Clause 6.13.3)

• Regularly paint glazing compound unless special materials used.
• Prevent corrosion of metal frames and warping of timber to avoid glass breakage.

Double/Multiple Glazing (Clause 6.9)

Glazing with Compound (Clause 6.4)

• Suitable for panes where height + width ≤ limits in Fig.1 (exposure grading).
• Ensure proper compound application and regular maintenance.

flowchart LR
    A[Routine Cleaning] --> B{Type of Glass}
    B -->|Transparent| C[Cloth or Wash Leather]
    B -->|Textured/Broken| D[Stiff Brush]
    A --> E[Stubborn Dirt?]
    E -->|Yes| F[Whiting or Methylated Spirits]
    E -->|No| G[Finish]
    G --> H[Regular Maintenance]
    H --> I[Paint Glazing Compound]
    H --> J[Prevent Corrosion & Warping]

For detailed limits on pane sizes and exposure, refer to Fig. 1 of IS 3548.

IS 3548 (1988) - Safety and Replacement Procedures Summary

1. Safety (Clause 6.13 Maintenance)

• Regular inspection and maintenance are mandatory to ensure safety.
• Check for wear, cracks, and deformation.
• Replace components if any defect compromises structural integrity.
• Follow manufacturer’s guidelines for maintenance intervals.

2. Replacement Procedures

• Remove damaged parts carefully without affecting adjacent components.
• Use identical or equivalent materials as per IS specifications.
• Ensure proper clearances during reassembly to avoid stress concentrations.

3. Clearances (Clause 2.1.2 & 2.1.7)

• Back Clearance and Edge Clearance must comply with Fig. 1A of IS 3548.
• Typical clearances ensure free movement and avoid interference.

Diagram: Clearance Concept (simplified)

flowchart LR
    A[Component Edge] -->|Edge Clearance| B[Adjacent Part]
    C[Back Surface] -->|Back Clearance| D[Supporting Surface]

For exact values and detailed figures, refer to Fig. 1A in IS 3548.