ROOFS

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.

Classification of roof based on shape

Pitched roof

Flat roof

Curved roof

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

and domes.

– Suitable for building to develop

architectural effect.

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.

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.

• 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)

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.

• 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

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

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

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.

Couple close roof

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

Collar beam roof

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.

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

King post truss

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.

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◦

Mansard Truss

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.

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.

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.

Types of flat roof Madras terrace roof

Bengal terrace roof

Reinforced brick cement roof

Reinforced cement concrete roof

Filler slab

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 provided.

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

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

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.

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.

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

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

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.

THANK YOU