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7.roofs

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7.roofs

  1. 1. ROOFS
  2. 2.  Topmost portion of a building  To give protection to building from rain,snow, wind,direct sunlight etc.  Types of roof depending upon the shape and material used.
  3. 3. Classification of roof based on shape Pitched roof Flat roof Curved roof
  4. 4. Pitched roof/sloping roof – Sloping top surface they are suitable for places where rainfall or snowfall is heavy.
  5. 5. • Flat roof – Suitable for moderate rainfall • Curved roof – Top surface curved in the form of shells and domes. – Suitable for building to develop architectural effect.
  6. 6. Technical terms used in pitched roof  Span:-  clear distance between the supports.  Rise:-  vertical distance between ridge and wall plate.  Pitch:-  ratio of rise to span.
  7. 7.  Ridge:- apex or headline of a slopping roof  Hip:- external angle formed at the intersection of two roof slopes.  Eaves :- lower edge of a sloping roof  Gable:-If roof slopes in two direction, the closing wall in that portion may be a combination of triangular and rectangular wall.The triangular upper part of the wall formed at the end of pitched roof is known as Gable.  Valley:-When two roof surfaces together at an angle less than 180 degree,a valley is formed.
  8. 8. • Purlins:- – wooden members are connected to trusses and to support common rafters – It placed horizontally over the principal rafter • Rafters:- – Inclined member placed above the purlins and extend from ridge to eave. – Common rafters are intermediate rafters, which give support to the roof covering (30-45cm spacing)
  9. 9.  Batten :-Small c/s of wood, fixed on common rafter to support roofing material.  Cleat:-Small pieces of steel or timber, angel or channel section, used to connect purlins to principal rafter.
  10. 10. • Types of pitched roof – Lean-to-roof – Couple roof – Couple close roof – Collar and tie roof – double or purlin roof – King post truss – Queen post truss – Mansard truss – Bel-fast truss – Steel truss Single roof truss
  11. 11. Lean-to-roof/shed roof  It is used covering verandah, sheds and outhouses connected to main building.  Upper side common rafters are supported on a wall plate which in turn rest on a projecting corbel stone from the wall.  Lower side rest on the wall plate.  Roofing material rests on battens, battens on common rafter and common rafter on wall plate.  Maximum span of the roof is 2.5m
  12. 12. Couple roof  It is formed by a pair of inclined rafters, centre ridge piece and wall plate for supporting the whole roof.  Battens are supported on common rafters and roofing material on battens  Span of couple roof is limited to 3.5m
  13. 13. Couple close roof  Similar to couple.  Two rafters are connected by a wooden member which acts as a tie.  Tie prevents the outward spreading of roof  It can also act as support for ceiling.  It can be economically used for spans up to 4.2m.
  14. 14. Couple close roof
  15. 15. Collar beam roof  Members are same but just raising the position of tie beam.  Used to increase the height of room  For spans between 4 to 4.5m
  16. 16. Collar beam roof
  17. 17. Collar and tie roof  For spans greater than 3m rafters are uneconomical  To reduce the size of rafters, intermediate supports called purlins  Roof can be economically adopted for spans up to 4.8m  Also known as purlin roof or double roof.
  18. 18. King post truss  Used when span > 5m  The triangular shape of truss frame offers greater rigidity.  Central vertical post-king post-provides support for tie beam.  Two inclined members provided on either side of king post- strut-used to prevent the principal rafter from bending at the Centre.  It is used for spans up to 5m to 8m
  19. 19. King post truss
  20. 20. Queen post truss  Two vertical post- queen post – 8m to 13m span  Straining beam is provided to keep upper end of queen post in position and to counteract the thrust of struts.  Straining sill is provided on the tie beam.
  21. 21. Mansard truss  Combination of king post and queen post.  Truss has two pitches.  Upper portion resembles a king post  Lower portion resembles a queen post  Pitch of upper part is 30 to 45◦  Pitch of lower part is 60 to 70◦
  22. 22. Mansard Truss
  23. 23. Bel-fast truss  Bowstring or latticed roof truss.  Thin sections of wood to form bow shaped.  Long spans up to 30m,with light roof covering materials.
  24. 24. Steel truss  Steel sections are available in all sizes and shapes can be used.  Members of steel truss is either in compression or tension  It have negligible bending.
  25. 25. Advantages of steel truss  Precast structures of desired dimension are available in market.  Termite and fire proof.  Light in weight and can be fabricated in any desired architectural form.  Strong,durable and long life.  Quickly and easily installed.
  26. 26. Types of flat roof  Madras terrace roof  Bengal terrace roof  Reinforced brick cement roof  Reinforced cement concrete roof  Filler slab
  27. 27. Madras terrace roof  Wooden flat roof  Roof having slope less than 1 in 100
  28. 28. Madras terrace roof  Steps in construction  Teak wood joist are placed on rolled steel joists.  Sufficient slope is provided  Terrace bricks of size 15x75x25mm to be laid diagonally.  Brick bat concrete of thickness 75mm to be laid  Rammed and allow to set for three days.  Flat tiles are then laid over this concrete.  Surface of this roof is finished with 3 coats of plaster.
  29. 29. Bengal terrace roof  Used for covering verandah portion.  Consists of rafters having slight inclination and one end penetrated into wall.  Battens are placed over this rafter with spacing 15cm.  Over that Flat tiles are laid in mortar.  Surface is finished with fine jelly concrete or flat tiles are provided.
  30. 30. Reinforced brick cement roof  Bricks are laid horizontally between the steel bars and concrete mix is inserted in the joints.  Top surface of the slab is plastered with a 2cm thick cement mortar.  Over that apply two layers of hot bitumen for water proofing.  Over that bitumen coat apply one more coat of cement paste of thickness 5cm.  Provide sufficient slope at top surface for drainage of water
  31. 31. Reinforced cement concrete roof  Made up of concrete and steel.  Types of roof slab:-  One way slab:- length/width > 2  Two way slab:- length/width < 2  For one way slab  Reinforcement to be run parallel to the shorter span  For two way slab  Main reinforcement runs parallel to both sides of the room  At corners suitable mesh reinforcement to be provided to resist temperature stresses
  32. 32. Filler slab  Concrete slab in which the bottom portion of the slab is replaced by flat clay tiles or Mangalore pattern tiles.  Above the formwork  Steel reinforcements of designed size are tied together to form a grid.  Pairs of clay roofing tiles are placed in the gap between the reinforcement in line.  Pour freshly prepared concrete in between the reinforcement and tiles.  Level the concrete surface and cured it for 14days.
  33. 33. Roof coverings • Gives a protective surface to the roofing structure. • Roof covering materials:-Thatching,tiling,slate,glass,asbestos sheet, G-I sheet. • Selection of covering materials depends on the type of building, roofing structure provided,climate,cost etc.
  34. 34. Asbestos cement sheets • Mixture of cement and asbestos • Suitable for roofing and are available – With corrugation – With wider channel • Heavy weight, thickness 3mm to 6mm • Durable, fire resistant and sound proof. • Disadvantage:- transfers heat and cold easily
  35. 35. Galvanized corrugated iron roofing  Corrugated iron sheet galvanized with zinc, to protect it from rusting in wet condition.  Light weight, thickness 0.15 to 1.8mm  Width of sheet is 60 cm to 85cm  Length 1m to 3.5m.  Easily corroded not able to resist fire and not sound proof  High initial and maintenance cost
  36. 36. PVC corrugated sheet  Made up of poly vinyl chloride plastic and other plastic like poly carbonate.  Different colors are now available.  Compared to other roofing material they are light weight,durable,fire resistant, rust free and give color full appearance to building.  Used in waiting shed, restaurant, porch etc.
  37. 37. THANK YOU

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