GENERAL
The roof 1s the upper-most protective corerng promied orer the baling Is
copec is to protect the building from rain hear wind snom ete It cossts of a
rame-work supported on walls or columns The irame-sork s orered by a
suitable covering material There are varios types of roos that can be sed
but selection of type of roof depends upon the span ype of bunding location
wind veiocity. intensity of snow-ialll beat insulation hgting and vennlano
etc. Sometimes. architectural consideration also decde the type o roof to be
sed. In this chapter only irame-worss required to support the root covering
wl be discussed. Roofcoverings have been discussedn the subsequent hapter.
22.1 CLASSIFICATION OF R0OFS
The roofs can be ciassified into following categories:
1.
1 Pitched or slopping roofs.
2. Flat roofs.
3 Shelled roofs.
4. Domed roofs.
All these categories of roofs have been discussed one by one.
22.1.1 Pitched or Slopping Roofs
This is the roof which is most commonly used for roofing large-spanned
structures like factory buildings. warehouses, workshops ete. in plain aeas
This type of roof is the only roof adopted in hilly areas and areas subjected to
extreme winds, rains and snow-falls. They are used not only for industnal
buildings but for residential buildings as well. Pitched roofs are the cheaper
than other types. This roof can be made from timber. structure steel. R.C.C.
and prestressed concrete. Roofs are termed as slopping or pitched. when their
angle of inclination exceeds about 10° with the horizontal. Angle of slope is
kept smal ifconditions of wind and rain are not severe and also snow-fall is not
, Buldng Constructton and Materials
likely to take place. As the conditions of rain wind and snow-fall become mora
and more critical slope of the roof is
increased
normally not allowed to exceed 60°. Pitched roofsproportionately. But slope is
may have their slope on both 5. Jack Rafters. Any rafter
the sides it may be
or
slopping
in direction only. shorter than the common rafter is known
one
jack rafter. as
22.2 IMPORTANT TECHNICAL TERMS
The definitions of some of the
important technical terms used in connection
with the pitched roofs are given below.
1. Span. The horizontal distance between
supports, supporting beams.
trusses or arches is known as span. The clear distance between
called clear span whereas horizontal distance between centres supports is
of supports is
known as effective span.
2. Rise of Trussed Roof. The vertical
height between wall plates and the
top of the ridge of the truss is known as rise.
3. Truss. It is a
structural element developed by joining various members
intotriangular frame-work. Tf truss developed exhibits top as triangular, it is
known as roofing truss. If developed frame-work is not triangular
known as bridging
truss.
but flat, it is Aud
4Pitch of the Roof. Inclination of the sides of the roof with the horizontal 2
is termed as pitch of the
roof. 1
5. Ridge. Apex line of the slopping roof is known as ridge. wa
6. Eaves. The lower
edges of roof which may be either
a
projecting beyond the supporting walls are known as eaves. resting upon or
7. Eaves Board.
Sometimes, a thin timber board is provided at the eaves to
cover the ends of the common (1) Ridge (2) Rafters
rafter. Such a board is called eaves board. It is
generally 15 cm wide and 2.5 cm thick in section. (3) Valley rafters (4) Jack rafters
(5) Hip rafters (6) Wall plates
8. Ridge Piece. It is a timber
piece which runs horizontally at the highest (7) Eaves boards
level ie. apex of a roof truss.
Common rafters are fixed to it at their
9. Valley. It is top. Fig. 22.1 Various parts of slopped roof.
depression formed at the intersection of two slopping
roofs at
their junction.
16. Valley Rafter. The rafters provided atslopetosupportthevalley gutters
10.Hip. It is a ridge formed by the intersection are known as valley rafters.
of two slopped surfaces
having an exterior angle greater than 180° 17. Template. A bedding block is always provided at the end of a truss. The
11. Hipped End. A bedding block is known as template. It may be made of wood, stone, or R.C.C.
slopped triangular surface formed at the end of the and its function is to spread the load over a large area of the wall.
slopping roof is called hipped end.
18.Wall Plate. These are timber members embedded in the walls to receive
12. Principal Rafter. It is a main inclined member of the truss the bottom ends of common rafters.
with the ridge of the truss. It
always bears compressive force. joining tie
19. Verge. The edge of slates, tiles, or sheets projecting beyond the gable
13. Common Rafter. These are
intermediate inclined end of the slopped roof is termed as verge. It may also be stated as the edge of a
over purlins from
ridge to the eaves. They are used to wooden members laid gable, running between the eaves and ridge.
coverings. They are usually spaced at 30 cm to 50 cm give support to the roof 20. Purlins. The wooden or steel horizontal members, placed on principal
14. Hip Rafters. They are the apart. rafters to carry the common rafters are known as purlins.
rafters, which are provided at the
two roof slopes forming hip of the junction ot
slopped roof. These rafters run from 21. Cleats. The small timber blocks fixed.on principalrafters, toprevent the
of the junction to the ridge and are used to corners cleats.
support the roof covering over the slidingdown of purlins, are known as
hip. They also support ends of purlins and jack rafters.
The roof 1s the upper-most protective corerng promied orer the baling Is
copec is to protect the building from rain hear wind snom ete It cossts of a
rame-work supported on walls or columns The irame-sork s orered by a
suitable covering material There are varios types of roos that can be sed
but selection of type of roof depends upon the span ype of bunding location
wind veiocity. intensity of snow-ialll beat insulation hgting and vennlano
etc. Sometimes. architectural consideration also decde the type o roof to be
sed. In this chapter only irame-worss required to support the root covering
wl be discussed. Roofcoverings have been discussedn the subsequent hapter.
22.1 CLASSIFICATION OF R0OFS
The roofs can be ciassified into following categories:
1.
1 Pitched or slopping roofs.
2. Flat roofs.
3 Shelled roofs.
4. Domed roofs.
All these categories of roofs have been discussed one by one.
22.1.1 Pitched or Slopping Roofs
This is the roof which is most commonly used for roofing large-spanned
structures like factory buildings. warehouses, workshops ete. in plain aeas
This type of roof is the only roof adopted in hilly areas and areas subjected to
extreme winds, rains and snow-falls. They are used not only for industnal
buildings but for residential buildings as well. Pitched roofs are the cheaper
than other types. This roof can be made from timber. structure steel. R.C.C.
and prestressed concrete. Roofs are termed as slopping or pitched. when their
angle of inclination exceeds about 10° with the horizontal. Angle of slope is
kept smal ifconditions of wind and rain are not severe and also snow-fall is not
, Buldng Constructton and Materials
likely to take place. As the conditions of rain wind and snow-fall become mora
and more critical slope of the roof is
increased
normally not allowed to exceed 60°. Pitched roofsproportionately. But slope is
may have their slope on both 5. Jack Rafters. Any rafter
the sides it may be
or
slopping
in direction only. shorter than the common rafter is known
one
jack rafter. as
22.2 IMPORTANT TECHNICAL TERMS
The definitions of some of the
important technical terms used in connection
with the pitched roofs are given below.
1. Span. The horizontal distance between
supports, supporting beams.
trusses or arches is known as span. The clear distance between
called clear span whereas horizontal distance between centres supports is
of supports is
known as effective span.
2. Rise of Trussed Roof. The vertical
height between wall plates and the
top of the ridge of the truss is known as rise.
3. Truss. It is a
structural element developed by joining various members
intotriangular frame-work. Tf truss developed exhibits top as triangular, it is
known as roofing truss. If developed frame-work is not triangular
known as bridging
truss.
but flat, it is Aud
4Pitch of the Roof. Inclination of the sides of the roof with the horizontal 2
is termed as pitch of the
roof. 1
5. Ridge. Apex line of the slopping roof is known as ridge. wa
6. Eaves. The lower
edges of roof which may be either
a
projecting beyond the supporting walls are known as eaves. resting upon or
7. Eaves Board.
Sometimes, a thin timber board is provided at the eaves to
cover the ends of the common (1) Ridge (2) Rafters
rafter. Such a board is called eaves board. It is
generally 15 cm wide and 2.5 cm thick in section. (3) Valley rafters (4) Jack rafters
(5) Hip rafters (6) Wall plates
8. Ridge Piece. It is a timber
piece which runs horizontally at the highest (7) Eaves boards
level ie. apex of a roof truss.
Common rafters are fixed to it at their
9. Valley. It is top. Fig. 22.1 Various parts of slopped roof.
depression formed at the intersection of two slopping
roofs at
their junction.
16. Valley Rafter. The rafters provided atslopetosupportthevalley gutters
10.Hip. It is a ridge formed by the intersection are known as valley rafters.
of two slopped surfaces
having an exterior angle greater than 180° 17. Template. A bedding block is always provided at the end of a truss. The
11. Hipped End. A bedding block is known as template. It may be made of wood, stone, or R.C.C.
slopped triangular surface formed at the end of the and its function is to spread the load over a large area of the wall.
slopping roof is called hipped end.
18.Wall Plate. These are timber members embedded in the walls to receive
12. Principal Rafter. It is a main inclined member of the truss the bottom ends of common rafters.
with the ridge of the truss. It
always bears compressive force. joining tie
19. Verge. The edge of slates, tiles, or sheets projecting beyond the gable
13. Common Rafter. These are
intermediate inclined end of the slopped roof is termed as verge. It may also be stated as the edge of a
over purlins from
ridge to the eaves. They are used to wooden members laid gable, running between the eaves and ridge.
coverings. They are usually spaced at 30 cm to 50 cm give support to the roof 20. Purlins. The wooden or steel horizontal members, placed on principal
14. Hip Rafters. They are the apart. rafters to carry the common rafters are known as purlins.
rafters, which are provided at the
two roof slopes forming hip of the junction ot
slopped roof. These rafters run from 21. Cleats. The small timber blocks fixed.on principalrafters, toprevent the
of the junction to the ridge and are used to corners cleats.
support the roof covering over the slidingdown of purlins, are known as
hip. They also support ends of purlins and jack rafters.
