1. ROOFS

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

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

4. Functional Requirements (cont’d)
Structural Stability
Provide a means of 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 – bend
To overcome : introducing a structural element which reduces the span

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

6. Functional Requirements (cont’d)
Provide Thermal Insulation
The roof constitutes a substantial proportion of the external surface area of a building & consequently has considerable potential for heat loss
Pitched roofs are usually insulated between the ceiling joists
Alternative insulation might be applied between rafters
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
Roof height & area increase with its horizontal dimension

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

10. SLOPING ROOF /PITCHED ROOF
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 & the requirements for underlayment & eave flashing
Slope roof planes may be combined to form a variety of roof forms

11. 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

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

13. 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.

14. 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

15. 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

16. 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

17. 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

18. 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

19. 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.

20. Types of Roof Coverings
Tiles
Thatch
Wood
Shingles
Tiles
Slates
Asphalt
Asbestos cement sheets
Corrugated iron sheets
Bituminous felt
Glass
Sheet metal roof coverings (copper, zink, etc.)
Thatch
Asbestos
Wood

21. 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