Code of practice for laying and fixing sloped roof coverings using plain and corrugated galvanized steel sheets

IS 12093: Scope & Key Specifications for Sloped Roofing with Steel Sheets

Scope Summary (Clause 3.1)

For efficient design and construction of sloped roofing with plain and corrugated steel sheets, the following must be determined:

• Surface area to be covered
• Type and arrangement of supporting elements
• Slope provision for drainage
• Fixing provisions for ridge pieces and services
• Level at which roof is to be installed

Important Design Considerations (Clause 2.3)

• Screws for plain sheets must conform to IS 6739-1972
• Screws shall be galvanised for corrosion resistance

Rounding Off Results (Clause 0.3)

• Final test or analysis values must be rounded as per IS 2-1960
• Retain the same number of significant digits as specified in the standard

Quick Reference Table: Screws for Plain Sheets

flowchart TD
    A[Start: Roofing Design] --> B[Determine Surface Area]
    B --> C[Select Supporting Elements]
    C --> D[Set Roof Slope for Drainage]
    D --> E[Plan Fixing of Ridge & Services]
    E --> F[Decide Roof Level]
    F --> G[Select Screws (IS 6739, Galvanised)]
    G --> H[Design & Construct Roof]

This concise scope ensures safe, durable, and efficient sloped roofing design using steel sheets per IS 12093.

IS 12093: Materials Specifications Summary

• Steel Sheeting (Clause 2.1):

  • Must conform to IS 277:1985 (Specification for galvanized steel sheets, plain and corrugated).
  • Coating grade options: 600 g/m² or 450 g/m² zinc coating.

• Screws (Clause 2.3):

  • For plain sheets, screws must conform to IS 6739:1972.
  • Screws shall be galvanized to prevent corrosion.

• Rounding Off (Clause 0.3):

  • Final test or calculation values must be rounded per IS 2:1960 rules, matching the significant figures of specified values.

Key Material Properties from IS 277 (Typical):

Important Design Inputs (Clause 3.1):

• Surface area coverage
• Support system type & layout
• Roof slope & drainage
• Ridge fixing details
• Installation level

flowchart TD
    A[Materials] --> B[Steel Sheeting]
    A --> C[Screws]
    B --> D[IS 277:1985]
    C --> E[IS 6739:1972]
    D --> F[Coating: 450 or 600 g/m²]
    E --> G[Galvanized Screws]

This ensures corrosion resistance and compliance for roofing steel sheets and fasteners.

IS 12093: Necessary Information & Key Design Data

Clause 3.1: Necessary Information for Sloped Roofing Design

For efficient design and construction of plain/corrugated steel sheet roofing, provide:

• Surface area to be covered
• Type and arrangement restrictions of supporting elements
• Slope provision for drainage
• Fixing provisions for ridge pieces and services
• Roof level where sheets are to be laid

Clause 4.1: Purlin Spacing for Steel Sheets

• At least one intermediate purlin is required on simple rafters to avoid sagging.
• For fabricated roof trusses, spacing depends on maximum allowable distances.

Additional Notes:

• Screws for plain sheets must conform to IS 6739-1972 and be galvanised.
• Round off test/analysis values per IS 2-1960 for compliance checks.

flowchart TD
    A[Start: Roofing Design] --> B[Gather Necessary Info]
    B --> C{Info Required}
    C -->|Surface Area| D[Area Measurement]
    C -->|Support Elements| E[Support Type & Restrictions]
    C -->|Slope| F[Drainage & Slope]
    C -->|Fixing Ridge| G[Ridge & Services Fixing]
    C -->|Roof Level| H[Level Determination]
    D & E & F & G & H --> I[Design Purlin Spacing]
    I --> J{Sheet Thickness}
    J -->|1.00 mm| K[Max Spacing 2.0 m]
    J -->|0.80 mm| L[Max Spacing 1.8 m]
    J -->|0.63 mm| M[Max Spacing 1.6 m]
    K & L & M --> N[Final Design]

This summary ensures you have the essential parameters and spacing guidelines for steel sheet roofing per IS 12093.

IS 12093: Design Considerations for Sloped Roofing with Steel Sheets

Key Points from Clause 4.1 (Design Considerations)

• Purlin Spacing (C/C) Based on Sheet Thickness:

• Purlin Placement:
  • At least one purlin at mid-span on simple rafters to avoid sagging.
  • End purlins required for each layer of sheets.
  • For fabricated trusses, purlin spacing follows maximum allowable distances.

Other Design Considerations (Clause 3.1)

• Determine surface area to be covered.
• Identify supporting elements and any restrictions.
• Ensure adequate slope for drainage.
• Plan for fixing ridge pieces and services.
• Specify the level at which the roof is laid.

Additional Specifications

• Screws for plain sheets must conform to IS 6739-1972 and be galvanized.
• Values should be rounded as per IS 2-1960 for compliance checks.

flowchart TD
    A[Start: Design Sloped Roof] --> B[Calculate Surface Area]
    B --> C[Select Steel Sheet Thickness]
    C --> D[Determine Purlin Spacing]
    D --> E{Simple Rafter?}
    E -->|Yes| F[Place End Purlins + Mid-span Purlin]
    E -->|No| G[Follow Truss Max Spacing]
    F --> H[Provide Slope & Drainage]
    G --> H
    H --> I[Fix Ridge Pieces & Services]
    I --> J[Set Roof Level]
    J --> K[Use IS 6739 Screws (Galvanized)]
    K --> L[Check Compliance & Round Values (IS 2)]
    L --> M[End]

This concise summary and table help ensure efficient design and construction per IS 12093.

IS 12093: Laying and Fixing of Corrugated Sheets – Key Points

1. Laps (Clause 4.3)

• Minimum End Lap: 150 mm
• Minimum Side Lap: 2 corrugations
• Laps can be increased to avoid cutting sheets, ensuring water tightness and structural integrity.

2. Fixing Specifications

• Hook Bolts: Use as per IS 12093 specifications for secure fastening of corrugated sheets.
• Slotted Round Head Wood Screws: Specified for fixing sheets to timber purlins.

3. General Practice for Laying Sheets

• Sheets should be laid from the eaves upwards.
• Overlaps must ensure no water ingress.
• Fixings should be at crest points of corrugations to avoid leakage.

Summary Table: Minimum Laps for Corrugated Sheets

flowchart TD
    A[Start at Eaves] --> B[Lay sheet]
    B --> C{Check overlap}
    C -- End Lap < 150mm --> D[Increase lap]
    C -- Side Lap < 2 corrugations --> D
    C -- OK --> E[Fix sheet at crest points]
    E --> F[Proceed to next sheet]

This ensures water tightness and structural stability as per IS 12093.

IS 12093: Ridges and Hips Key Specifications

1. Overlap and Laps (Clause 6.1)

• Minimum lap on either side: 150 mm over roofing sheets.
• End laps between ridges and hips: Not less than 150 mm.
• Ridges and hips must be properly bent to shape and fixed.

2. Fixing Details (Clause 6.2)

• Use J or 2 M6/M8 hook bolts for fixing to roof members.
• At least one fixing bolt must pass through the end laps on either side.
• If not possible, provide extra hook bolts.
• End laps joined by at least two M6 hook bolts per lap.
• Laps must be set in red lead for sealing.
• Edges must be straight and surfaces plane & parallel to roof plane.
• Ridges/hips must fit squarely on sheets.

3. Hole Making (Clause 5.6)

• Holes for bolts/rivets in crown of corrugations, drilled (not punched).
• Washer holes exactly match hook bolt diameter.
• Nuts tightened from above for leak-proofing.

Summary Table:

flowchart LR
    A[Ridges & Hips] --> B{Lap}
    B -->|Sides| C[≥ 150 mm]
    B -->|End lap| D[≥ 150 mm]
    A --> E[Fixing]
    E --> F[J or 2 M6/M8 hook bolts]
    E --> G[At least one bolt through end lap]
    E --> H[2 M6 bolts per end lap]
    A --> I[Hole Making]
    I --> J[Drilled holes in corrugation crowns]
    I --> K[Exact bolt diameter]
    A --> L[Se

IS 12093: Valleys and Flashings - Key Specifications & Formulas

1. Valleys and Flashings Dimensions & Fixing (Clause 7.1)

• Width & Thickness: As specified by design or manufacturer.
• Lap with Corrugated Sheets: Minimum 150 mm on either side.
• End Lap: Minimum 150 mm, painted with red lead for corrosion protection.
• Shape: Bent to required profile and fixed securely.

2. Fixing Requirements (Clause 5.6 & 6.2)

• Holes for bolts/rivets must be drilled in the crown of corrugations (not punched).
• Washers' holes must match hook bolt diameter exactly.
• Nuts tightened from above to ensure a leak-proof roof.
• Valleys and flashings fixed with J or M6/M8 hook bolts.
• End laps joined with at least two M6 hook bolts, set in red lead.
• Edges of valleys/flashings must be straight and plane when fixed end-to-end.

3. Lapping & Joint Protection

4. Additional Notes

• Sheets should not be built into gables/parapets.
• Edges bent up near walls and sealed with flashing or bitumen mastic gola.

Summary Diagram of Lap & Fixing:

flowchart LR
    A[Corrugated Sheet] -->|Lap 150 mm| B[Valley/Flashing]
    B -->|End Lap 150 mm| C[Valley/Flashing End]
    C -->|M6 Hook Bolts (≥2)| D[Fixed Joint]
    D -->|Red Lead Paint| E[Corrosion Protection]

Use these guidelines to ensure proper installation, durability, and waterproofing of valleys and flashings as per IS 12093.

IS 12093: Fastening Details for Corrugated Steel Sheets

Key Specifications & Formulas:

• Riveting (Clause 5.5):

  • Rivet diameter: 6 mm galvanized wrought iron
  • Washers: 2 galvanized plain round washers per rivet
  • Spacing:
    • Side lap: max 200 mm
    • End lap: rivet on every corrugation (staggered)
  • Rivets must be tightly drawn; avoid indentation on sheet surface.

• Laps (Clause 4.3):

  • End lap: minimum 150 mm
  • Side lap: minimum 2 corrugations
  • Laps may be increased to avoid cutting sheets.

• Screws (Clause 2.3):

  • Must conform to IS 6739-1972
  • Must be galvanized

• Hook Bolts (Clause 5.3):

  • Types: 7 or L hook bolts, M6 or M8 size
  • Projection above nut: ≥ 12 mm
  • Grip length on purlin side: ≥ 25 mm
  • Minimum 3 hook bolts per sheet per purlin at ridges
  • Spacing ≤ 300 mm

Summary Table:

flowchart TD
    A[Steel Sheet] --> B[Side Lap: 2 Corrugations]
    A --> C[End Lap: 150 mm]
    B --> D[Riv

IS 12093: Quality and Inspection - Key Points

• Rounding Off Values:
  As per Clause 0.3, all test or analysis results must be rounded off following IS 2:1960 guidelines:

  • Round off to the same number of significant digits as specified in the standard.
  • Use standard rounding rules (e.g., 0.5 and above rounds up).

• Quality Control & Inspection:
  Although IS 12093 lacks explicit tables/formulas for quality and inspection, typical practices include:

  • Visual Inspection: Check for defects, dimensional accuracy.
  • Dimensional Tolerances: Follow specified limits in the standard or related IS codes.
  • Material Testing: Use standard test methods (e.g., tensile, hardness).
  • Sampling Plans: Adopt statistical sampling per IS 2500 or IS 4905.

• General Specification Tips:

  • Ensure compliance with specified mechanical properties.
  • Maintain traceability of test certificates.
  • Follow IS-approved test procedures and calibration standards.

Rounding Off Example (IS 2:1960)

If you need detailed inspection criteria or testing methods, refer to IS 2500 (sampling) or IS 1608 (tensile test).