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ROOFS

ROOFS. Roof. Top most part of building Protects building from rain, wind, direct sunlight, snow etc Classification based on Shape - sloping, flat, curved Materials used- tiled, concrete, thatched. REQUIREMENTS OF A ROOF.

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ROOFS

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  1. ROOFS

  2. Roof • Top most part of building • Protects building from rain, wind, direct sunlight, snow etc • Classification based on • Shape- sloping, flat, curved • Materials used- tiled, concrete, thatched

  3. REQUIREMENTS OF A ROOF • It should have adequate strength and stability to carry the dead and live loads. • Should protect the building against rain, sunlight, wind, etc • It should be waterproof and should have efficient drainage arrangements. • It should provide adequate thermal insulation & fire resistant. • It should provide adequate insulation against sound.

  4. Sloping/ Pitched roof • Sloping top surface • Suitable for places where rainfall / snowfall is heavy • Used in coastal areas

  5. PARTS

  6. TERMS • SPAN: clear distance between the supports of an arch, beam or roof truss. • RISE: vertical distance between the top of the ridge and the wall plate. • PITCH: inclination of the sides of a roof to the horizontal plane. • RIDGE: the apex line of the sloping roof. • HIP: ridge formed by the intersection of two sloping surfaces, where the exterior angle is greater than 180˚

  7. VALLEY:reverse of a hip. It is formed by the intersection of two roof surfaces, making an external angle less than 180˚ • RAFTERS: inclined members running from the ridge to the eaves. They are fixed to purlins at intermediate point. They support the battens to support the roof coverings. • PURLINS: horizontal wooden or steel members, used to support common rafters of a roof when span is large. • WALL PLATE: Member placed just above the wall to hold the rafters

  8. TYPES OF PITCHED ROOF • LEAN TO ROOF • COUPLE ROOF • COUPLE CLOSE ROOF • COLLAR BEAM ROOF • COLLAR & TIE ROOF(PURLIN ROOF) • KING POST TRUSS • QUEEN POST TRUSS • STEEL TRUSS

  9. LEAN TO ROOF(Shed roof)

  10. LEAN TO ROOF SIMPLE TYPE USED FOR COVERING VERANDAH, SHEDS& OUT HOUSE CONNECTED TO MAIN BUILDING UPPERSIDE- WALL PLATE REST ON CORBEL STONE LOWER SIDE- WALL PLATE Max. span= 2.5m

  11. COUPLE ROOF • Formed by pair of inclined rafters, • Centre ridge & wall plates • Battens are supported on rafters • Span 3.5m

  12. COUPLE CLOSE ROOF • 2 rafters are connected by a wooden member-tie beam • Tie prevents outward spreading of roofs & supports ceiling • Span up to 4.2m

  13. COLLAR BEAM ROOF • Modified form of couple close roof • Position of tie beam is just raised-collar beam • Used to increase the ht: of room • Span 4-4.5m

  14. COLLAR & TIE ROOF(PURLIN ROOF)

  15. To reduce the c/s size of rafters for span > 3m, intermediate supports are introduced under the rafter- purlin • Span up to 4.8m

  16. KING POST TRUSS • Central vertical post used to support tie beam-king post • Struts-2 inclined members provided on either side of king post. Used to prevent bending on principal rafter • Span 5-8m • Used when • Span >5m • Intermediate supports for purlins & ties are unavailable

  17. QUEEN POST TRUSS • Queen post- 2 vertical post • Consist of 2 principal rafters, struts, tie beams, purlins, straining beam • straining beam-horizontal beam which keeps upper end of queen post in position & to counteract the thrust of struts • Span 8-13m

  18. Mansard truss • Combination of kingpost truss and queen post trusses • Truss has 2 pitches • Upper part-30-45˚ • Lower part - 60-70˚

  19. BEL-FAST ROOF TRUSS • It is also called Bow-string roof truss since it is in the form of a bow, with its top chord being curved. • This can be used up to a span of 30 m if the roof covering is light.

  20. STEEL TRUSS • When the span exceeds 10m, timber trusses become heavy and uneconomical. • Steel trusses are used economically over larger spans. • Mild Steel Sections are available in different size & shapes.

  21. STEEL TRUSS

  22. Advantages • Precast structures of desired dimensions are available • Termite & fire proof • Light in weight • Can be fabricated in any form • Strong & durable • Quickly &easily installed

  23. Flat /terraced Roof • Roof laid at an angle <10˚ • Slope for easy drainage • Used in multi storey constructions. • Advantages- • Terrace can be used for playing & domestic purposes • Simple construction & maintenance • Good insulating property & fire resisting • More stable against wind • No need of false ceiling • Upper floor can be constructed • Need less roofing materials

  24. Disadvantages • Can’t be used for long spans without columns & beams • Not suitable for heavy rainfall areas • High initial cost • Slowly construction compared to truss • Cracks may develop due to temperature variation • If proper slope is not provided for drainage, the water may get collected, causing leaks

  25. TYPES OF FLAT ROOFS • RCC flat roof • Filler slab • Madras terrace roof • Bengal terrace roof • Reinforced brick cement roof

  26. RCC flat roof • Made up of concrete & steel • Consist of RC flat slab which covers the distance b/w supports • Steel reinforcement is provide at the bottom to resist the tensile forces • For greater spans some of the bars are bend up to the top at the supports • Easy to construct • Provides smooth finishing surface • Thickness of slab depends on • Type of concrete • Span • Floor loads

  27. TYPES • Depending on the ratio of length n width of the room • 1 way slab Ly/Lx > 2 • 2 way slab Ly/Lx < 2

  28. Filler slab

  29. Bottom portion of the slab is replaced by flat clay/MP tiles • Top portion-compression • Bottom portion-tension • Tensile force is carried by reinforcement so concrete in that portion is replaced by cheaper filler materials • Above formwork steel reinforcements are tied together to form a grid • Pairs of tiles are placed in the gap b/w the reinforcement • Freshly prepared concrete is pored in b/w the reft & tiles & compact it carefully • Level the concrete surface & cure it for 14 days

  30. Advantages • Reduces cost of construction • Provides better insulating property • Amount of concrete can be reduced by 50% • More attractive

  31. Madras terrace roof/wooden flat roof • Slope < 1 in 100 Construction procedure • Teak wood joists are placed on rolled steel joists • Furring piece is placed b/w wooden joist & RSJ for giving sufficient slope • Terrace bricks (15x75x25mm) are laid diagonally across joists

  32. Brick bat concrete (75mm thick) is laid & rammed and allowed to set for 3 days • 2 course of flat tiles are laid over the concrete • Surface of roof is finished with 3 coats of plaster

  33. Bengal terrace roof • Rafters are placed with slight inclination at 30m centre to centre or 50m centre to centre • Battems are placed at right angles to rafters at 15m centre to centre • A course of flat tiles is laid in mortar over battens. • Finally roof is finished by applying 2 or more course of flat tiles with 2-3 coats of plaster OR • A layer of jelly concrete 40mm thick may be laid over flat tiles

  34. REINFORCED BRICK CEMENT ROOF • Bricks are laid horizontally between steel bars and concrete mix was inserted into joints • Top surface is plastered with 20mm thick cement mortar • Over that apply hot bitumen coat or cement paste coat of 50mm thick • Thickness of slab may be 100mm to 200mm • This type of roof is used upto span 4m

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