S1-S2 BT

1. ROOFS

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. Classification of roof based on shape
Pitched roof
Flat roof
Curved roof

4. Pitched roof/sloping roof
– Sloping top surface they are suitable for places where
rainfall or snowfall is heavy.

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. 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.  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. • 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.  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. • 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. 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. 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. 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. Couple close roof

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. Collar beam roof

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. 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. King post truss

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. 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. Mansard Truss

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. 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. 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. Types of flat roof
 Madras terrace roof
 Bengal terrace roof
 Reinforced brick cement roof
 Reinforced cement concrete roof
 Filler slab

27. Madras terrace roof
 Wooden flat roof
 Roof having slope less than 1 in 100

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. 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. 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. 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. 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. 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. 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. 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. 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.

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