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ROOFS

ROOFS. 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. Functional Requirements (cont’d).

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ROOFS

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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: 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: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 • 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 Ridge

  16. Common Term Used (cont’d)

  17. Common Term Used (cont’d)

  18. Common Term Used (cont’d)

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

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