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  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 • 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

  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 • 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 • Roof represents a large proportion of the external surface area of a building has 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:SlopingFlatsShellDomes

  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

  10. Shed Gable Hip Gambrel Mansard Saw tooth

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

  12. SLOPING ROOF (cont’d) • 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

  13. 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

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

  15. 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.

  16. 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

  17. Common Term Used Ridge

  18. Common Term Used (cont’d)

  19. Common Term Used (cont’d)

  20. Common Term Used (cont’d)

  21. 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.

  22. Types of Roof Coverings • 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. • Wood-thin, tapered pieces of wood primarily used to cover roofs and walls of buildings to protect them from the weather • Shingles-roof covering consisting of individual overlapping elements. Can be made of various materials such as wood, composite or ceramic. Thatch Wood

  23. 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. Tiles

  24. 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. • 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-bitumenmixed 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

  25. 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