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IS 1346:1991 is the Indian Standard (BIS) for waterproofing of roofs with bitumen felts. This code covers the recommended procedures for waterproofing roofs using bitumen felts. It provides guidelines on surface preparation, application of bitumen primer, proper laying techniques (overlaps and staggering), and outlines the specifications for four-course, six-course, and seven-course waterproofing treatments.
Code of Practice for Waterproofing of Roofs with Bitumen Felts
! Ensure the roof surface is completely dry, clean, and appropriately sloped before applying the bitumen primer to ensure maximum adhesion.
! Always start laying the felt from the lowest point of the roof slope (near the drain) and proceed upwards towards the ridge to prevent water ingress at the overlapping joints.
! End laps in adjacent rolls must be staggered to avoid the formation of continuous weak joints.
BS 8217:2005BSI - British Standards Institution, UK
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Reinforced bitumen membranes for roofing. Code of practice
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DIN 18531-1:2017DIN - Deutsches Institut für Normung, Germany
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Waterproofing for roofs not used for traffic - Part 1: Requirements, design principles
Specifies requirements for planning, design, and execution of waterproofing for non-utilized roofs.
NRCA Roofing Manual: Membrane Roof Systems - 2021NRCA - National Roofing Contractors Association, USA
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The NRCA Roofing Manual: Membrane Roof Systems
Provides industry best-practice guidelines for the design and application of membrane roofing, including Built-Up Roofing (BUR).
IBC 2021, Chapter 15ICC - International Code Council, USA
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Roof Assemblies and Rooftop Structures
A building code chapter that mandates requirements for roof assemblies, including material and application standards for built-up roofs.
Key Differences
≠IS 1346 is prescriptive about traditional felts (as per IS 1322) and hot bitumen. International standards like BS 8217 cover a wider range of modern materials, including polymer-modified bitumen (SBS, APP) and cold-applied systems.
≠IS 1346 specifies a minimum roof slope of 1 in 60. Modern international standards (NRCA, IBC) typically require a steeper minimum slope, often 1/4" per foot (approx. 1 in 48), to ensure positive drainage and prevent ponding water.
≠International standards (e.g., IBC referencing ASCE 7) have extensive, engineered requirements for wind uplift resistance based on building height, location, and exposure. IS 1346 lacks this level of detailed wind-load design criteria.
≠BS 8217 and DIN 18531 include detailed methodologies for condensation risk analysis and specify performance requirements for Vapour Control Layers (VCLs), which are more advanced than the basic vapour barrier provisions in IS 1346.
Key Similarities
≈All standards are founded on the principle of creating a continuous, multi-layer impermeable barrier using bitumen-saturated felts, forming a monolithic membrane.
≈A critical and common requirement across IS 1346 and its international counterparts is the meticulous preparation of the substrate to be clean, dry, smooth, and properly graded before application begins.
≈The technique of applying multiple layers of felt with staggered and specified minimum overlaps (side and end laps) is a fundamental practice common to all standards to ensure membrane continuity.
≈All standards emphasize the importance of correct detailing at critical failure points, such as roof drains, parapet walls, and penetrations, specifying minimum upstand heights and reinforcement.
Parameter Comparison
Parameter
IS Value
International
Source
Minimum Roof Slope for Drainage
1 in 60
1:48 (1/4 inch per foot)
NRCA Roofing Manual / IBC 2021
Minimum Upstand Height at Parapets/Walls
150 mm above finished roof level
200 mm (8 inches) minimum above finished roof surface
NRCA Roofing Manual
Minimum Side Lap of Felt
75 mm
75 mm (3 inches) for ply sheets
BS 8217:2005
Minimum End Lap of Felt
100 mm
150 mm (6 inches) for ply sheets
NRCA Roofing Manual
Hot Bitumen Application Temperature Control
Prescriptive maximum temperature (e.g., not above 200°C)
Performance-based: Apply within +/- 14°C (25°F) of the material's Equiviscous Temperature (EVT)
NRCA Roofing Manual
Typical Number of Plies (New Built-Up Roof)
4 to 7 courses (layers of felt and bitumen)
2 to 4 plies
IBC 2021 (Table 1507.10.2)
⚠ Verify details from original standards before use
Key Values4
Quick Reference Values
Minimum side overlap for bitumen felts75 mm
Minimum end overlap for bitumen felts100 mm
Recommended slope for flat roofs1 in 60 (minimum 1 in 100)
Nominal application rate of bitumen bonding material per coat1.2 kg/m²
Tables & Referenced Sections
Key Tables
Table 1 - Details of Waterproofing Treatments (Four, Six and Seven Course)