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
Classification of roof based on shape
Pitched roof/sloping roof
– Sloping top surface they are suitable for places where
rainfall or snowfall is heavy.
• Flat roof
– Suitable for moderate rainfall
• Curved roof
– Top surface curved in the form of shells
– Suitable for building to develop
Technical terms used in pitched roof
clear distance between the supports.
vertical distance between ridge and
ratio of rise to span.
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
– wooden members are connected to trusses and to support common
– It placed horizontally over the principal rafter
– Inclined member placed above the purlins and extend from ridge to
– Common rafters are intermediate rafters, which give support to the
roof covering (30-45cm spacing)
Batten :-Small c/s of wood, fixed on common rafter to support
Cleat:-Small pieces of steel or timber, angel or channel section, used
to connect purlins to principal rafter.
• Types of pitched 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
It is used covering verandah, sheds
and outhouses connected to main
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
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
Span of couple roof is limited to 3.5m
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.
Collar and tie roof
For spans greater than 3m rafters are uneconomical
To reduce the size of rafters, intermediate supports called
Roof can be economically adopted for spans up to 4.8m
Also known as purlin roof or double roof.
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
It is used for spans up to 5m to 8m
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.
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◦
Bowstring or latticed roof truss.
Thin sections of wood to form bow shaped.
Long spans up to 30m,with light roof covering materials.
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.
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
Strong,durable and long life.
Quickly and easily installed.
Madras terrace roof
Wooden flat roof
Roof having slope less than 1 in 100
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.
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
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
Provide sufficient slope at top surface for drainage of water
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
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
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
• 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.
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
• Disadvantage:- transfers heat and cold
Galvanized corrugated iron roofing
Corrugated iron sheet galvanized with
zinc, to protect it from rusting in wet
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
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
Used in waiting shed, restaurant, porch