Roofs come in various types depending on the building, climate, and available materials. Pitched roofs slope in one or multiple directions and include gable, hip, and gambrel styles. Flat roofs are constructed of reinforced concrete and can be one-way slabs, two-way slabs, slab-and-beam, or flat slabs resting directly on columns. Roof coverings include thatch, slates, tiles, asbestos sheets, corrugated metal, shingles, and more, with the selection based on factors like cost, durability, and appearance.

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ROOFS
Introduction
 It is the top most component of the building which gives
protection against various climatic conditions.
Type of building , local climate conditions and material
available for the construction are main factors deciding type of
roof or roof covering.

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Types of roof
 Roofs of specific shapes are provided to enhance the beauty
of building.
 According to the shapes, the following are the types of
roofs.
1) Sloping roof or pitched roof
2) Flat roof or slab or terrace roof
3) Shell roof
4) Dome

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Types of Pitched roof
 Lean to roof: Roof sloping in one direction. It is used for small span. e.g.
Verandah
 Gable roof: Sloping on both the sides. Slope of the roof depends on local climate
conditions. Region with heavy rain fall or snow fall need roofs with relatively
steep slope.
 Hip roof: Slope in all four directions.
 Gambrel roof: Slope in two directions. The slopes are not continuous but there is
a break in slope.
 Mansard roof: Like hip roof it has slope in four directions. The slope is not
continuous but has a break.
 Deck roof: It has slopes in all four directions but has deck on the top instead of a
ridge.
 Monitor roof and Saw tooth roof: Mainly used for industrial building and serve
the purpose of good ventilation and light under the roof.

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TERMINOLOGIES
Following are various terminologies used for pitched roof.
 Span: The clear distance between the supports of arch, beam or roof truss
.
 Rise of roof: It is the vertical distance between the wall plate and top of
the ridge.
 Pitch of roof: The inclination of sides of a roof to the horizontal is
termed as pitch of roof.
 Eaves: The lower edge of the inclined roof surface of a pitched roof is
termed as eaves.
 Ridge: Apex of the angle formed by the termination of the inclined
surface at the top of a slope.
 Valley: It is the acute angle formed by the intersection of two slope in a
pitched roof.

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TERMINOLOGIES
 Hip: It is the ridge formed by intersection of two sloped surface having
an exterior angle greater than 180 degree.
 Gable: It is a triangular portion of the wall of a sloped roof formed by
continuing the end wall up within the roof. Thus gable have two slopes
with ridge in between.
 Verge: The edge of the sheets, slates or tiles, projecting beyond the gable
end of sloped roof.
 Common rafter: These are inclined wooden members laid from the ridge
to eaves.They are bevelled against the ridge piece at the head and are
fixed to the purlins at intermediate points. They are usually spaced 30 to
40 cm apart.
 Eaves board or facia board: It is a wooden plank of generally 25mm
thick and 15cm wide fixed along the eaves connecting feet of common
rafters.

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TERMINOLOGIES
 Purlins: Horizontal members of wood or steel used to support common
rafters.
 Cleats: These are short sections of wood or steel, nailed, screwed or
bolted to the rafters of the truss for supporting purlins.
 Wall plates: Timber pieces which are provided over the top of the stone
or brick wall for the purpose of fixing the feet of common rafter.
 Template: This is a block of stone or concrete provided under the end of
tie beam to spread the load from roof over a larger area of bearing.
 Hip rafters: Rafters which form hip of a sloped roof. These rafters run
from the ridge to the corner of the wall to support the covering over the
hip. They met the end of purlins and jack rafters.

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TERMINOLOGIES
 Jack rafters: These are rafters, shorter in length, extend from
hip or valley to the eaves.
 Valley rafters: These are rafters provided at slope to support
the valley gutters.
 Battens: Small scantlings which are nailed to the rafters for
laying tiles, over the sloped roof.
 Truss: The wooden or steel frame work used to support the
roof is called truss. Used for long span of roof.

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Lean to roof
 Verandah not exceeding 2.5m in span is covered by this type
of roof.
 One end of roof is supported by a wall plate resting on corbel
whereas the other end is resting on the wall plate supported
on a wooden post.
 A string course is provided in the wall just above the upper
end of the roof for preventing the leakage of rain water in
verandah.
 The roof covering is fixed to the battens which rest on rafter.
Wooden boards can also be fixed directly on rafters.

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Couple Roof
 Used for a room spanning about 3.5m.
 Two rafters are fixed to the ridge piece at the top.
 The lower ends of the rafters rest on the wall plates which are
supported on the wall.
 The rafters are provided at some specific distances to
distribute the roof load evenly.
 Roof covering is provided on battens which are fixed to the
rafters.

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Couple close roof
 Similar to the couple roof with the only difference that rafters
are connected by tie beam.
 The tie beam connect two walls and serves for fixing ceiling.
 This roof is suitable up to a span of 4.5m.

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Collar roof
 It is suitable for a span ranging between 4 to 5.5m.
 In this type of roof rafters are supported by a collar tie.
 Collar tie is provided at 1/2 or 1/3 of vertical height between
ridge and wall plate.
 The collar has same sections as that of the rafters.
 The collar is connected to rafters by dovetail joint.
 Bolts also may be fixed for additional strength.

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King Post Truss
 It is suitable for roofs of span varying from 5m to 8m.
 It consists of a central post known as king post, forms a
support for the tie beam.
 The inclined members known as struts, prevents the principal
rafters from bending in the middle.
 At the top common rafters are placed which is supported on
purlins.
 Roof covering are placed over common rafter.

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Mansard truss
 It is a combination of king post and queen post truss.
 It is useful for construction of gambrel roof.
 There is and advantage of utilizing the space below the
sloping roof.

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Steel truss
 Mild steel is strong in compression and tension. Therefore
large span buildings are made up of steel.
 Steel is also preferred for fire proof construction.
 The type of steel truss is decided considering the span,
roofing material and distance between two consecutive
trusses.
 Steel trusses are designed in such a way that the members
may be in either tension or compression. No member is
subjected to bending stress.
 The tension members should be preferably flat or round
sections.

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Roof Covering
 Roof covering is the material provided on the roof skeleton.
 It is provided on wooden battens and acts as a protecting barrier for rain, wind , sun
etc.
 Some of the roof covering are described below.
1. Thatch
 It is the oldest material used as roof covering but is almost obsolete now a days.
 Some times it is used in low cost rural houses and cattle shed.
 The truss if required is constructed using bamboos. The common rafters are also
made up of bamboos provided 30cm apart.
 The bamboo chips are fixed on rafters and thatch is supported on chips by ropes or
strings.
 Thatch covering is about 15cm thick and the slope of the roof is kept 40 to 50
degrees.
 Thatch is combustible and absorbs moisture. It is also liable to decay by insects and
pests. Chemical treatment is given to make it fire proof and insect proof.
 It is changed after 2 to3 years.

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Roof covering
2. Slates
 The roofing slates are available in the sizes ranging from
60cm x 35cm to 25cm x 12.5cm.
 Thickness of the sheet varies from 1.5mm to 4.5mm for small
sizes and it varies from 9 to12mm for large sizes.
 The slates are fixed to the wooden battens using nails or zinc,
copper or galvanized iron.
 This type of roof covering is very strong.

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Roof covering
3. Tiles
 Two types of tiles are used as roof covering.
(a) Flat, curved pan tiles and half round country tiles.
 These tiles are available readily and are provided on the framework
consisting of battens fixed on common rafters.
 Ridge, valley and hips are formed using specially mounded tiles.
(b) Manglore tiles
 These tiles are better than half round country or other tiles and have
identical shape, size and colour.
 As they are properly burnt, they are more durable and have minimum
breakage.
 The battens are fixed on the common rafters according to the shape of
grooves in the tiles.
 Boarding is treated with tar paint for making it insect proof.

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Roof covering
4. Asbestos-cement sheet
 Asbestos-cement sheets are readily available in the market as big six
sheets which are corrugated and as trafford sheet which are semi
corrugated.
 The asbestos roofing is light, cheap, impervious, durable ad fire
resisting. It is widely used for industrial building.
5. Galvanised corrugated iron sheets
 This sheets are also readily available and used extensively as roof
covering for factory, workshop etc.
 This roof covering is durable , fire proof, light in weight and does not
require maintenance.
 The sheets are laid with end lap of not than 15cm and side lap of 1.5 to
2 corrugations. They are fastened to the purlin by means of galvanised
iron hook bolts, screws and nails.

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Roof covering
6. Shingles
 Wooden shingles cut form the well seasoned timber are
used as roof covering.
 It is mainly used in hilly areas where wood is available
easily.
 The shingles have length, varying between 30 to 38 cm and
widths varying between 6 to 25 cm.
 They are fixed in the similar way as tiles.

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Factors affecting selection of roof covering
 Initial cost
 Maintenance cost
 Slope of the roof
 Durability
 Fire resistance
 Load of the covering
 Type of construction
 Appearance
 Thermal conductivity

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Flat Roofs
 Flat roof of concrete are widely used in construction.
 Reinforced cement concrete is used for planning and design of roofs of
different shapes and dimensions.
 The RCC roofs are of following types.
1) One way slab
 It is suitable for small span.
 When length of room is greater than 1.5 time its width the RCC slab is
designed as spanning in one direction.
 The slab is either resting on wall or may be designed as compound member
with the end beams.
 The thickness of slab is 12cm minimum and the main reinforcing steel is
provided parallel to the short side and is not less than 0.15 percent of the
cross sectional area of concrete.
 The distribution steel is provided for shrinkage and temperature stresses
induced in RCC slab.

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Flat Roofs
2. Two way reinforced slab
 When the room is nearly square or long side is less than 1.5 time small
side, the slab is designed as spanning in two directions.
 The main reinforcement is provided in both the directions.
3. Slab and beam construction
 For larger span, the roof is designed as a slab with T-beam .
 This type of construction gives uneven ceiling.
 When levelled ceiling is required this type of design is not useful.
 However the gap between two consecutive beams is filled up by hollow
tiles and levelled ceiling is finished using plaster.

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Flat roof
5. Composite steel and concrete roof
 The roofing slab especially for a large span is supported on I section of
rolled steel joists.
 The I section behaves like a central beam.
 Sometimes upper web of I section is embedded in concrete or entire I
section is embedded in the concrete.
To enhance the aesthetical beauty of the building specially curved RCC
roof is also constructed.
Shell roofs of different shapes can also be constructed using RCC. The
shell roofs are suitable for industrial building.
RCC domes are used as roof for temples or monumental structures.
Madras terrace roof and jack arch roof are also flat roofs.

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Flat roof
4. Flat slab
 The flat slab is directly resting on the columns. The type of
construction is very simple its design is done in a specific
manner.
 Following are advantages of flat slab.
 There are no beams, so there is no unevenness in the ceiling and more
head room is available.
 According to design thinner section of the slab is required for identical
load.
 The cost of formwork is less and thus the total cost is reduced.