GENERAL FUNCTION: To give a protective covering to the building, so rain, wind or snow may not damage the building

1. ROOFS

2. ROOF
GENERAL FUNCTION:
• To give a protective covering to the building, so
rain, wind or snow may not damage the building
Functional requirements
1. Weather resistance
2. Structural stability
3. Provide good appearance
4. Provide thermal insulation

3. Functional Requirements (cont’d)
Weather Resistance
1. Required to protect a building from the damaging effects of rain & wind
2. The ingress of rain: causes damage to decorations & structural damage to
timber due to attacks by fungus & insects
3. The roof is covered by a layer of impermeable material which prevents
the passage of rain into a building
4. The deflection of building may be cause of wind

4. Functional Requirements (cont’d)
Structural Stability
• Provide support for the roof covering
• In designing a roof structure, the designer must take into
consideration the span of structural members
• If span at joist too great will cause bending
• To overcome : introducing a structural element which reduces
the span

5. Functional Requirements (cont’d)
Provide Good Appearance
1. Might be a major visual element in the design of a building
2. The detailing of roof can significantly affect the appearance
of a building

6. Functional Requirements (cont’d)
Provide Thermal Insulation
1. Roof represents a large proportion of the external surface area of a
building has potential for heat loss.
2. Pitched roofs are usually insulated between the ceiling joists
3. Alternative insulation might be applied between rafters
4. Flat roof insulation is usually laid above the decking, either below
or above the roof covering

7. •General types of roofs:
Sloping
Flats
Shell
Domes

8. SLOPING ROOF / PITCHED ROOF
• Sloping roof may be categorized into:
 Medium to high slope – 4:12 to 12:12
 Low slope - up to 3:12
• Sloping roofs shed water easily to eave gutters (drain/sewer).
• Roof height & area increase with its horizontal dimension

9. This type of roof depends on:-
•Area covered
•Materials available
•Type of lighting
•Ventilation needed inside
•Available appliance
Type of roof Description
Shed roof Simplest type and slopes only in 1 direction.
Use for smaller span
Gable roof Slopes in 2 directions, commonly used
Hip roof Slopes in 4 directions
Gambrel roof Slopes in 2 directions, but there is a break in slope
Mansard roof Slopes in 4 directions, but there is a break in slope
Saw-tooth / north light roof Used in factories where light is admitted from the
glazing fixed on the steep sloping sides of the
roof.

11. Shed
Mansard
Gambrel
Hip
Saw tooth
Gable

12. SLOPING ROOF (cont’d)
• Sloping roofs may have a structure of:
1. Rafters & sheathing
2. Beams, purlins & decking
3. Trusses

13. • Medium & high slope roofs may be covered with shingles, tiles or sheet
materials
• Low slope roofs require roll or continuous membrane roofing; some
shingle & sheet materials may be used on 3:12 pitches
• The roof slope also affects the design loads.
• Slope roof planes may be combined to form a variety of roof forms
SLOPING ROOF (cont’d)

14. FLAT ROOFS
• Pitch from 0 to 10 degree
• Slope may be achieved by sloping the structural members or by
tapering the deck or rigid insulation
• Slope usually leads to interior drains; perimeter scuppers can be
used as overflow drains

15. FLAT ROOFS (cont’d)
• Roof structure may consist of:-
1. Joist & sheathing
2. Beams & decking
3. Flat trusses
4. Concrete slabs
• Flat roofs require continuous membrane roofing
Deck

16. Shell Roof
• A thin shell is defined as a shell with a thickness which is small compared to
its other dimensions and in which deformations are not large compared to
thickness
• These elements are typically curved and are assembled to large structures.
Example: factories and roof structures in some buildings.
• Advantage in construction : a lot of material is saved as the section needed
is very thin.

17. Domes
• A roof of semi-spherical or semi elliptical shape
• Constructed of stone or brick or concrete, & supported on
circular or regular polygon shaped walls
• The structure is such that within certain height & diameter
ratios, very small thickness is needed

18. Common Term Used
Term Description
Ridge piece A member which runs horizontally at the highest level of
the roof
Hip External angle of a sloping roof at which the roof slopes
are turned down
Common rafter Members supporting the battens or boardings under the
roof covering
Hip rafter Members which form the hip of the roof & to which the
common rafters are attached
Ridge

19. Common Term Used (cont’d)
Ridge Apex line of a sloping roof
Eaves The lower edges of the sloping surface of a roof
Eave-board Wooden board fixed along the eaves connecting the common rafters
Gable Wall which follows the slope of the roof from eave to ridge & covers
the end of a roof
Barge
board
Wooden planks used to fix the ends of common rafters projecting
beyond the sloping top of a gable wall

20. Common Term Used (cont’d)
Valley A depression formed at the intersection of two sloping roofs at their
junction
Jack rafter Short lengths of rafters fixed at the hip rafters & eaves board
Valley rafter Member at the intersection of 2 inverted slopes to which rafters are
fixed
Dragon beam Short member of wood which carries the foot of a hip rafter which is
attached to the tie fixed across the angle formed by the intersection of 2
wall plates at the corner of a building
Purlins Members that laid horizontally to support the common rafters. They
transmit the loads to the trusses or walls

21. Common Term Used (cont’d)
Purlin cleat Short piece of timber bolted to the rafters of
roof truss for fixing the purlins
Truss A framework of triangles

22. ROOF COVERINGS
• Is a materials which gives a protective surface to the roofing
structure
• The function is only to prevent ingress or egress of heat & moisture
into the building
• Various types of coverings depending on :-
 The character of the building
 The type of the roofing structure
 Local conditions, cost, etc.

23. Types of Roof Coverings
1. Thatch- is the craft of building a roof with dry
vegetation such as straw, water reed, sedge, rushes,
or heather. Now become choice for rustic look and
more ecologically friendly roof.
2. Wood- thin, tapered pieces of wood primarily used
to cover roofs and walls of buildings to protect them
from the weather
3. Shingles- roof covering consisting of individual
overlapping elements. Can be made of various
materials such as wood, composite or ceramic.
Thatch
Wood

24. Tiles
4. Tiles-made of a ceramic material and is hard and brittle,
poorly suited for places where tree limbs can fall on a house's
roof.
5. Slates - is a fine-grained, foliated,
homogeneous metamorphic rock derived from an
original shale-type sedimentary rock composed
of clay or volcanic ash
6. Asphalt – known as bitumen, viscous liquid or semi solid
form of petroleum.

25. 7. Asbestos cement sheets-known as fibre cement
sheet. It is a building material in which asbestos
(silicate mineral) fibres are used to reinforce thin rigid
cement sheets.
8. Corrugated iron sheets-The corrugations
increase the bending strength of the sheet. Normally
each sheet is manufactured longer in its strong
direction.
9. Bituminous felt-bitumen mixed with a filler
component such as limestone or sand or polymers to
gives rigidity and tear resistance.
10. Sheet metal roof coverings (copper, zink,
etc.)-roofing system made from metal piece, or tiles.
Asbestos

26. ROOF DESIGN & CONSTRUCTION FACTORS
• Roof structure must be designed to carry:
 Dead loads – roof structure, deck, insulation, roofing & any
equipment located on top of or suspended from roof
 Live loads – accumulated rain, snow & ice & traffic if any.
 Wind loads – pressure or suction from wind
• Type of roofing required against:
 Surface water from the outside
 Water vapor diffusion from the inside
 Moist air flow
 Heat flow & solar radiation