Short Notes: Roofs | Short Notes for Civil Engineering - Civil Engineering (CE) PDF Download

 Page 1


CHAPTER – 13 
ROOFS 
 
A roof is defined as the uppermost part of a building which is 
constructed in the form of a frame work to given protection to the 
building against rain, heat, snow, wind etc. A roof basically consists of 
structural elements provided at the top of building for the support of roof 
coverings. 
Following are the requirements of well planned roof: 
(i) It should be durable against the adverse effects of various 
agencies such as wind, rain, sun etc. 
(ii) It should grant the desirable insulation against sound and heat. 
(iii) It should be structurally stable and sound, it should be capable of 
taking the loads likely to come over it. 
(iv) It should be well-drained 
(v) It should have efficient water-proofing arrangement. 
 
13.1 Types of roofs-Methods of construction: 
 The roofs classified into the following three categories; 
(i) Pitched roofs 
(ii) Flat roofs 
(iii) Curved roofs 
I. Pitched roofs: A sloping roof is known as pitched roof as 
shown in the fig 13.1. The technical terms in connection with 
the pitched roof are given below 
 
Page 2


CHAPTER – 13 
ROOFS 
 
A roof is defined as the uppermost part of a building which is 
constructed in the form of a frame work to given protection to the 
building against rain, heat, snow, wind etc. A roof basically consists of 
structural elements provided at the top of building for the support of roof 
coverings. 
Following are the requirements of well planned roof: 
(i) It should be durable against the adverse effects of various 
agencies such as wind, rain, sun etc. 
(ii) It should grant the desirable insulation against sound and heat. 
(iii) It should be structurally stable and sound, it should be capable of 
taking the loads likely to come over it. 
(iv) It should be well-drained 
(v) It should have efficient water-proofing arrangement. 
 
13.1 Types of roofs-Methods of construction: 
 The roofs classified into the following three categories; 
(i) Pitched roofs 
(ii) Flat roofs 
(iii) Curved roofs 
I. Pitched roofs: A sloping roof is known as pitched roof as 
shown in the fig 13.1. The technical terms in connection with 
the pitched roof are given below 
 
Roofs                                                                                          
  
 
 
Fig 13.1  Building with pitched roof 
 
(i) Barge Boards: Wooden planks or boards which are 
fixed on the gable end of the roof 
(ii) Battens: Thin strips of wood which are fixed on 
rafters or ceiling to support the roof ceiling. 
(iii) Cleats: Small blocks of wood which are fixed on truss 
to prevent the sliding of purlins. 
(iv) Dragon beam: The diagonal piece of wood which is 
laid across the corner of the wall. 
Page 3


CHAPTER – 13 
ROOFS 
 
A roof is defined as the uppermost part of a building which is 
constructed in the form of a frame work to given protection to the 
building against rain, heat, snow, wind etc. A roof basically consists of 
structural elements provided at the top of building for the support of roof 
coverings. 
Following are the requirements of well planned roof: 
(i) It should be durable against the adverse effects of various 
agencies such as wind, rain, sun etc. 
(ii) It should grant the desirable insulation against sound and heat. 
(iii) It should be structurally stable and sound, it should be capable of 
taking the loads likely to come over it. 
(iv) It should be well-drained 
(v) It should have efficient water-proofing arrangement. 
 
13.1 Types of roofs-Methods of construction: 
 The roofs classified into the following three categories; 
(i) Pitched roofs 
(ii) Flat roofs 
(iii) Curved roofs 
I. Pitched roofs: A sloping roof is known as pitched roof as 
shown in the fig 13.1. The technical terms in connection with 
the pitched roof are given below 
 
Roofs                                                                                          
  
 
 
Fig 13.1  Building with pitched roof 
 
(i) Barge Boards: Wooden planks or boards which are 
fixed on the gable end of the roof 
(ii) Battens: Thin strips of wood which are fixed on 
rafters or ceiling to support the roof ceiling. 
(iii) Cleats: Small blocks of wood which are fixed on truss 
to prevent the sliding of purlins. 
(iv) Dragon beam: The diagonal piece of wood which is 
laid across the corner of the wall. 
(v) Eaves: The lower edge of a roof which are resting 
upon or projecting beyond the supporting walls are 
known as eave as shown in the fig 13.2 
(vi) Gable: The triangular upper part of a wall formed at 
the end of a pitched roof is known as gable. 
(vii) Hip: The angle formed at the intersection of two roof 
slopes is known as hip. 
(viii) Pitch: The inclination of sides of a roof to the 
horizontal plane is known as pitch, expressed in 
degrees or as a ratio of rise to span. 
(ix) Purlins: The wooden pieces which are placed 
horizontally on principal rafters to carry the common 
rafters are known as purlins. 
(x) Rafters: There are the pieces of timber which extend 
from the caves to the ridge 
a) Common rafters : These are the intermediate 
rafters, which give support to the roof coverings 
a shown in the fig 13.2. 
b) Hip rafters: Which provided at the junction of 
two roof slopes 
c) Jack rafters: Any rafters, which is shorter than 
common rafters is known as Jack Rafters. 
d) Principal rafters : These are the inclined 
members of a truss 
Page 4


CHAPTER – 13 
ROOFS 
 
A roof is defined as the uppermost part of a building which is 
constructed in the form of a frame work to given protection to the 
building against rain, heat, snow, wind etc. A roof basically consists of 
structural elements provided at the top of building for the support of roof 
coverings. 
Following are the requirements of well planned roof: 
(i) It should be durable against the adverse effects of various 
agencies such as wind, rain, sun etc. 
(ii) It should grant the desirable insulation against sound and heat. 
(iii) It should be structurally stable and sound, it should be capable of 
taking the loads likely to come over it. 
(iv) It should be well-drained 
(v) It should have efficient water-proofing arrangement. 
 
13.1 Types of roofs-Methods of construction: 
 The roofs classified into the following three categories; 
(i) Pitched roofs 
(ii) Flat roofs 
(iii) Curved roofs 
I. Pitched roofs: A sloping roof is known as pitched roof as 
shown in the fig 13.1. The technical terms in connection with 
the pitched roof are given below 
 
Roofs                                                                                          
  
 
 
Fig 13.1  Building with pitched roof 
 
(i) Barge Boards: Wooden planks or boards which are 
fixed on the gable end of the roof 
(ii) Battens: Thin strips of wood which are fixed on 
rafters or ceiling to support the roof ceiling. 
(iii) Cleats: Small blocks of wood which are fixed on truss 
to prevent the sliding of purlins. 
(iv) Dragon beam: The diagonal piece of wood which is 
laid across the corner of the wall. 
(v) Eaves: The lower edge of a roof which are resting 
upon or projecting beyond the supporting walls are 
known as eave as shown in the fig 13.2 
(vi) Gable: The triangular upper part of a wall formed at 
the end of a pitched roof is known as gable. 
(vii) Hip: The angle formed at the intersection of two roof 
slopes is known as hip. 
(viii) Pitch: The inclination of sides of a roof to the 
horizontal plane is known as pitch, expressed in 
degrees or as a ratio of rise to span. 
(ix) Purlins: The wooden pieces which are placed 
horizontally on principal rafters to carry the common 
rafters are known as purlins. 
(x) Rafters: There are the pieces of timber which extend 
from the caves to the ridge 
a) Common rafters : These are the intermediate 
rafters, which give support to the roof coverings 
a shown in the fig 13.2. 
b) Hip rafters: Which provided at the junction of 
two roof slopes 
c) Jack rafters: Any rafters, which is shorter than 
common rafters is known as Jack Rafters. 
d) Principal rafters : These are the inclined 
members of a truss 
Roofs                                                                                         
  
(xi) Ridge: A wooden piece provided at the ridge line of a 
sloping roof is known as ridge or ridge board or ridge 
piece 
(xii) Span: The horizontal distance between the internal 
faces of walls or supports is known as span or clear 
span. 
(xiii) Template: A bidding block generally provided at the 
end of a truss. This block is known as template and it 
helps in spreading load over a large area. A  template 
may be of wood or stone or R.C.C. 
(xiv) Verge: The edge of a gable, running between the 
caves and ridge is known as a verge 
(xv) Valley: When two roof surfaces meet together and 
form an internal angle, a valley is formed 
(xvi) Wall-plate: These are long wooden members which 
are embedded on top of walls to receive the common 
rafters 
 
Fig 13.2   Truss 
Page 5


CHAPTER – 13 
ROOFS 
 
A roof is defined as the uppermost part of a building which is 
constructed in the form of a frame work to given protection to the 
building against rain, heat, snow, wind etc. A roof basically consists of 
structural elements provided at the top of building for the support of roof 
coverings. 
Following are the requirements of well planned roof: 
(i) It should be durable against the adverse effects of various 
agencies such as wind, rain, sun etc. 
(ii) It should grant the desirable insulation against sound and heat. 
(iii) It should be structurally stable and sound, it should be capable of 
taking the loads likely to come over it. 
(iv) It should be well-drained 
(v) It should have efficient water-proofing arrangement. 
 
13.1 Types of roofs-Methods of construction: 
 The roofs classified into the following three categories; 
(i) Pitched roofs 
(ii) Flat roofs 
(iii) Curved roofs 
I. Pitched roofs: A sloping roof is known as pitched roof as 
shown in the fig 13.1. The technical terms in connection with 
the pitched roof are given below 
 
Roofs                                                                                          
  
 
 
Fig 13.1  Building with pitched roof 
 
(i) Barge Boards: Wooden planks or boards which are 
fixed on the gable end of the roof 
(ii) Battens: Thin strips of wood which are fixed on 
rafters or ceiling to support the roof ceiling. 
(iii) Cleats: Small blocks of wood which are fixed on truss 
to prevent the sliding of purlins. 
(iv) Dragon beam: The diagonal piece of wood which is 
laid across the corner of the wall. 
(v) Eaves: The lower edge of a roof which are resting 
upon or projecting beyond the supporting walls are 
known as eave as shown in the fig 13.2 
(vi) Gable: The triangular upper part of a wall formed at 
the end of a pitched roof is known as gable. 
(vii) Hip: The angle formed at the intersection of two roof 
slopes is known as hip. 
(viii) Pitch: The inclination of sides of a roof to the 
horizontal plane is known as pitch, expressed in 
degrees or as a ratio of rise to span. 
(ix) Purlins: The wooden pieces which are placed 
horizontally on principal rafters to carry the common 
rafters are known as purlins. 
(x) Rafters: There are the pieces of timber which extend 
from the caves to the ridge 
a) Common rafters : These are the intermediate 
rafters, which give support to the roof coverings 
a shown in the fig 13.2. 
b) Hip rafters: Which provided at the junction of 
two roof slopes 
c) Jack rafters: Any rafters, which is shorter than 
common rafters is known as Jack Rafters. 
d) Principal rafters : These are the inclined 
members of a truss 
Roofs                                                                                         
  
(xi) Ridge: A wooden piece provided at the ridge line of a 
sloping roof is known as ridge or ridge board or ridge 
piece 
(xii) Span: The horizontal distance between the internal 
faces of walls or supports is known as span or clear 
span. 
(xiii) Template: A bidding block generally provided at the 
end of a truss. This block is known as template and it 
helps in spreading load over a large area. A  template 
may be of wood or stone or R.C.C. 
(xiv) Verge: The edge of a gable, running between the 
caves and ridge is known as a verge 
(xv) Valley: When two roof surfaces meet together and 
form an internal angle, a valley is formed 
(xvi) Wall-plate: These are long wooden members which 
are embedded on top of walls to receive the common 
rafters 
 
Fig 13.2   Truss 
 
Types of pitched roofs: 
(i) Single roof 
(ii) Double or purlin roof 
(iii) Trussed roofs 
 
(i) Single roof: In this type of roofs, common rafters are provided to 
each slope without any intermediate support. The following are 
the varieties of single roof. 
a) Lean to roof 
b) Couple roof 
c) Couple close roof 
d) Collar beam roof 
a) Lean to roof: It is the simplest form of a pitched roof and it is 
known as pent roof or Aisle roof. In this type of roof, one wall is 
carried up sufficiently higher than the other to give necessary slope 
to the roof. A lean-to roof is generally used for sheds, out-houses 
attached to main buildings verandah etc. This is suitable for a 
maximum span of 2.40m as shown in fig 13.3.