The 1984 edition of IS 2858 outlines the recommended practices for installing roofs using machine-produced burnt-clay Mangalore tiles, prevalent throughout India. This standard details design criteria, materials, installation techniques, waterproofing methods, and finishing approaches to achieve weather-tight, durable roofing systems. It is intended for architects, engineers, and construction specialists working on both residential and commercial projects involving these tiles.
Overview
The 1984 edition of IS 2858 outlines the recommended practices for installing roofs using machine-produced burnt-clay Mangalore tiles, prevalent throughout India. This standard details design criteria, materials, installation techniques, waterproofing methods, and finishing approaches to achieve weather-tight, durable roofing systems. It is intended for architects, engineers, and construction specialists working on both residential and commercial projects involving these tiles.
Audience
Contents
Structure
This section defines the extent and key parameters for applying Mangalore tile roofing according to IS 2858. Design must consider the roofing surface area, the type and layout of structural supports, treatment of junctions with walls, provisions for slope and drainage, and methods for securing ridge tiles. Dead load values for different roof constructions are specified to ensure proper structural calculations, with examples and formulas provided for calculating total dead load based on area and roof covering weight.
Essential terms and definitions relevant to Mangalore tile roofing are provided to ensure consistent understanding. This includes explanation of materials, components, and testing methods. Guidelines for rounding off test results in accordance with IS 2:1960 are included, along with specifications for sheet metal used in valley gutters, requiring galvanized metal with minimum 1.25 mm thickness, and references to related material standards.
Key design considerations such as calculating surface area, supporting element arrangements, junction treatments, roof slope, drainage, and ridge tile fixing provisions are emphasized. Completion of the roof framework with reepers nailed in place is mandatory before tiling. Dead loads for various configurations are tabulated. Codes for timber structure design, preservation, and wire specifications for fixing are referenced to ensure durability and structural integrity.
This section focuses on the roof's ability to shed rainwater effectively to prevent leaks. Proper tile interlocking and laying ensure waterproof joints, supplemented by drainage systems including corrugation channels, gutters, and downpipes. Valley gutters require galvanized sheet metal extending under the roof and into walls with mortar fixing. Minimum roof slopes and drainage flow calculations are discussed to maintain efficient runoff.
Detailed specifications for materials including sheet metal for valley gutters, roofing tiles, and fixings are presented. Dead load values for different roof types are summarized. Inspection checkpoints during installation are outlined to identify potential failures such as sagging or water ingress. Referenced standards for cement, lime, wire nails, and clay tiles inform material selection and quality assurance.
Guidance on scheduling roof installation activities stresses completing the structural framework prior to tile laying. Reepers must be securely nailed in position, and galvanized wire per IS 280:1978 should be used for tying tiles to resist corrosion and provide adequate strength. Design data collection and coordination among stakeholders are essential to ensure a smooth workflow.
Flat tiles should be soaked for two hours, dried, and optionally dipped on the underside in a creamy whitewash before installation. Mangalore tiles also require soaking for at least two hours. When laid over flat tiles with mortar bedding, the mortar thickness should be at least 25 mm, and for roofs with pitches exceeding 30°, fillets spaced approximately 1 meter apart must be fixed to retain flat tiles.
Reepers must be fixed over rafters at specified intervals, with nails penetrating a minimum of 20 mm into rafters. They should extend over at least three spans and be joined only by butting over rafters, with joints staggered between rows. Timber specifications and treatment against decay and termites are mandated to ensure longevity. Nails used should be galvanized plain headed types conforming to relevant standards.
Tiles must be thoroughly soaked and laid with mortar bedding of at least 25 mm thickness. Roof pitches between 24° and 45° are recommended, with increased pitch and additional fixing methods for areas experiencing heavy rainfall or elevated locations. Minimum head laps of 75 mm and appropriate side laps per tile design are essential for waterproofing. Options for underlayers include flat tiles with or without mortar, and ceiling tiles with metal flat ties.
Full tiles should be installed surrounding roof projections like chimneys to maintain structural integrity. Flashing made from metal or bitumen must cover the interface between the tiling and the projection, turned against the projection, draped over tiles, and securely embedded into masonry joints with wedging and pointing to ensure water tightness. Specifications for tile overlaps, mortar thickness near valleys, and additional reepers placement are provided.
To prevent water ingress at roof-wall junctions, tiles must be embedded into walls at a depth of at least 50 mm. A drip moulding positioned approximately 100 mm above the roof surface should be constructed. Joints between roof and wall are to be grouted with waterproof mortar. Where gutters or flashings are absent, these measures are critical. Metal saddles of minimum 45 cm² area are recommended under hip-ridge junctions for enhanced waterproofing.
Regular inspections should verify that reepers have no joints except over joists and that tilting fillets are properly fixed to prevent sagging or cracking. Tile laying must avoid alignment of joints with underlying flat tiles or ceiling tiles to maintain interlocking and prevent leaks. Prompt replacement of damaged tiles and upkeep of proper interlocking are vital to roof durability. Dead load adherence and material specifications for valley gutters also ensure sustained performance.
Frequently Asked
IS 2858 Clause 4.2 specifies that roofs using Mangalore tiles should have a minimum pitch of 24° and a maximum of 45°. In locations with heavy rainfall or elevated terrain, the minimum slope should be increased beyond 24° to improve weather protection. Additional measures such as securing tiles with screws or wire ties and using protective layers like roofing felt or mortar-bedded flat tiles are advised. A minimum head lap of 75 mm is required if not inherently provided by tile design to ensure effective water drainage.
To achieve watertight joints, both flat and Mangalore tiles must be soaked in water for at least two hours prior to installation. Flat tiles should be laid on reepers after optionally dipping their undersides in whitewash and drying. A mortar bed of at least 25 mm thickness must be spread over flat tiles, with Mangalore tiles fully embedded into this layer. For roof slopes exceeding 30°, fillets spaced approximately one meter apart should be fixed to hold flat tiles in place. Tiles should be set with a minimum head lap of 75 mm and properly interlocked. When installed against walls, tiles must be embedded at least 50 mm with a drip moulding above and joints sealed with waterproof mortar.
Reepers must be constructed from structural timber species listed in IS 883:1970 and treated against decay and termites as per IS 401:1982. The minimum cross-section sizes are 50 x 25 mm for Mangalore tiles over flat tiles and 50 x 15 mm for tiles directly on reepers or ceiling tiles on reepers. Rafter spacing should not exceed 600 mm unless otherwise designed. Reepers are fixed over rafters with plain-headed galvanized nails penetrating at least 20 mm, extending over three spans, and butt joints only allowed over rafters, with joint staggering between adjacent rows to maintain strength and stability.
Valley gutters should be fabricated from galvanized steel sheets with a minimum thickness of 1.25 mm and a width of 1.2 m. They must overlap joints by at least 300 mm along the slope and be laid on top of reepers rather than nailed underneath. Two additional reepers sized 50 x 25 mm should be positioned about 150 mm from the valley centerline on each side to support tiles and mortar. Roof sides adjacent to valleys are plastered with a 12 mm mortar layer to prevent seepage. Ridge tiles must be edge-bedded in mortar, properly interlocked with broken joints, and finished with plaster or paint matching tile color. Hip and ridge junctions require leak-proof grouting, and optional use of metal saddles with a minimum area of 45 cm² beneath these joints is recommended.
For waterproofing roof-wall intersections, tiles should be embedded into the wall at a minimum depth of 50 mm to create a secure seal. A drip moulding approximately 100 mm above the roof surface must be installed to divert water away from the wall. All joints between the roof and wall are to be sealed with waterproof mortar or an equivalent material. When gutters or flashings are absent, these measures become essential to prevent leakage. Compliance with relevant Indian Standards on waterproofing is recommended to enhance durability and protection.
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