This code of practice outlines comprehensive instructions for waterproofing roofs with bitumen felts, detailing the selection, surface preparation, application methods, and upkeep of waterproofing systems suitable for flat, pitched, timber, and shell roofs. It is an indispensable resource for professionals aiming to enhance building durability by preventing water penetration through effective waterproofing.
Overview
This code of practice outlines comprehensive instructions for waterproofing roofs with bitumen felts, detailing the selection, surface preparation, application methods, and upkeep of waterproofing systems suitable for flat, pitched, timber, and shell roofs. It is an indispensable resource for professionals aiming to enhance building durability by preventing water penetration through effective waterproofing.
Audience
Contents
Structure
This section defines the extent of the code, covering specifications for bituminous materials and waterproofing treatments used on roofs. It references relevant standards for terminology and material testing, including IS 702, IS 1203, IS 1322, IS 3067, IS 3384, IS 4911, IS 7193, IS 1609, and IS 1834. Designers are directed to ensure compliance with IS 3067 regarding roof structure and finishing details influencing waterproofing.
This part summarizes necessary reference standards and design data, highlighting the importance of adhering to IS codes for materials and application methods. It specifies minimum quantities of hot-applied bitumen (≥ 2.5 kg/m²) and gravel or grit (0.008 m³/m²) for effective waterproofing. Designers should integrate information from IS 3067 related to roof design, felt coverings, and finishing.
Key terms used throughout the code are defined primarily in reference to IS 4911:1986. Definitions include bitumen felt composition, types of bitumen applications, primer use, and classification of felts by base material and finish. Typical application rates for primers, bitumen, felts, and optional gravel layers are also detailed.
Designers are advised to consult IS 3067:1988 for comprehensive guidance on roof design, selection of waterproofing materials, and finishing treatments. Important factors include material compatibility, durability, surface preparation, waterproofing detailing, and maintenance planning. Minimum roof slope recommendations for drainage effectiveness are also provided.
This section outlines the grades of industrial bitumen suitable for bonding and top dressing, including Grades 85/25, 90/15, and 115/15 for vertical surfaces. It specifies bitumen application rates, types of bitumen felts (hessian, glass fibre, fibre base), and top dressing aggregates like pea gravel or coarse sand. Primer requirements per IS 3384 are also covered.
Describes various waterproofing treatments such as floating, heavy, and normal, including the number of layers, types of felts, and quantities of hot bitumen and gravel used. Special instructions for timber roofs and notes on minimum application rates and material quality are included.
Details the step-by-step method for laying bitumen felt waterproofing, including priming, bonding of successive felt layers with hot bitumen, and proper placement of gravel or grit. Different treatment systems such as light, floating, and heavy treatments are explained with corresponding layer descriptions and application rates.
Provides guidelines for routine inspection and maintenance of bitumen felt waterproofing, emphasizing preparatory cleaning, treatment of gutters and flashings, application of top finishes, and removal of surplus materials. It reiterates material quantity standards and references relevant IS codes for quality assurance.
Lists the Indian Standards cited throughout the code, encompassing specifications for industrial bitumen (IS 702), testing methods (IS 1203), bitumen felts (IS 1322), laying procedures (IS 1609), sealing compounds (IS 1834), tiles (IS 2690, IS 1237), damp-proofing design (IS 3067), primers (IS 3384), glossary (IS 4911), and glass fibre felts (IS 7193). These references support comprehensive material and procedural compliance.
Frequently Asked
The code recommends using industrial blown bitumen Grades 85/25 or 90/15 for bonding between felt layers and roof surfaces. For vertical surfaces up to 1 meter, these grades apply, while above 1 meter, Grade 115/15 is advised. For roofing felts, hessian-based self-finished felts (Type 3, Grade 1), glass fibre base felts (Type 2, Grade 1), and fibre-base self-finished felts (Type 2, Grade 1 or 2) are suitable. These felts must comply with IS 1322 and IS 7193 standards to ensure durability and waterproofing effectiveness.
Prior to waterproofing, the roof surface should be thoroughly cleaned to remove dirt, moss, fungus, and other debris using wire brushing and dusting. The substrate, including any cement or lime work, must be fully cured and dry. A minimum slope of 1:100 should be provided to facilitate drainage and prevent water pooling. A bitumen primer conforming to IS 3384, typically industrial blown bitumen Grade 85/25 or 90/15, should be applied uniformly and allowed to dry completely before laying the bitumen felt layers.
The process begins by applying a primer coat to the roof or gutter surface. The first bitumen felt layer is bonded to this primed surface using hot applied bitumen adhesive. Subsequent felt layers are similarly bonded with hot bitumen, ensuring that joints overlap appropriately to prevent water ingress. For gutters, at least two layers of felt are required, each bonded with hot bitumen. This multilayer bonding technique guarantees durable and continuous waterproofing.
Parapet walls should have flashing felts installed with minimum 100 mm laps, ensuring the lower edge overlaps roof felts and the upper edge is securely tucked into grooves within the parapet. Joints between flashing layers should be staggered and sealed. Masonry and timber parapets require slightly different approaches, with timber flashings secured over felt turn-ups and angle fillets using battens. Gutters need separate flashings carried under roof eaves, with an extra felt layer in shell roof valley gutters. All joints must be properly sealed and laps maintained at 100 mm to preserve waterproofing continuity.
To maximize durability, regular inspections especially before monsoon seasons should be conducted to identify and repair any damages early. The roof surface must be kept clean, dry, and primed properly before application. Use industrial blown bitumen Grades 85/25 or 90/15 for bonding, and ensure all joints and overlaps are sealed with hot bitumen. Drainage outlets should be maintained clear to prevent water accumulation. Vertical surfaces must be coated with appropriate bitumen grades depending on height, and mechanical damage from foot traffic should be avoided to maintain waterproofing integrity.
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