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Chapter 5
- 1. BACHELOR OF QUANTITYSURVEYING (HONS) BLD 60104 CONSTRUCTION TECHNOLOGY 1 By Azrina Md Yaakob Azrina.MdYaakob@taylors.edu.my CHAPTER 5 ROOFING
- 2. 1.1 FUNCTION • Tokeep out rain, wind, snow & dust • To prevent excessive heat loss in winter • To keep the interior building cool in summer • Designed to accommodate all stresses encountered • Designed to accept movement due to changes in temperature & moisture content • To provide lateral restraint & stability to adjacent walls • To resist penetration of fire & spread of flame from external sources
- 3. 1.2 TYPES OFROOF TYPES Pitched Flat Gambrel & Mansard Shed Gable/ Hip
- 4. 1.2.1 FACTORS THATINFLUENCE THE TYPE OF ROOF CHOSEN a) Size and shape of buildings • Simple shape: pitched roof • Irregular shaped: flat roof • Clear span b) Appearance • Small: pitched roof • Large: flat roof c) Economics • Capital & maintenance cost d) Others • Services accommodated • weatherproofing
- 5. 1.2.2 PITCHED ROOF • Any roof whose angle of slope to the horizontal lies between 10 and 70 degree • Pitch is determined by the covering that is to be placed over the timber carcass, governed by the load & span • Higher cost than flat roof • Create a useful void for locating cold water storage system • Material : Timber : structural softwood; members joined together with nails
- 10. 1.2.2.1 PITCHED ROOFMEMBERS Ridge • Spine of a roof • Pitching plate for the rafters that are nailed to each other through the ridge board Hipped end • The roof slope is continued around the end of a building, where the wall is carried up to the underside of the roof at a gable end Rafters • Splay cut / bevelled & nailed to ridge board at upper ends & birth-mouthed nailed to wall plate at lower ends
- 11. Hip rafters • Framethe external angles at the intersection of roof slopes Valley rafters • Used at internal angles Jack rafters • The shortened rafters running from hip rafters to plate & from ridge to valley rafters
- 12. Common rafters • Mainload-bearing members of a roof • Span between a wall plate at eaves & ridge • Notched over & nailed to wall plate situated on top of a load-bearing wall Wall plates • Provide the bearing & fixing medium for various roof members • Distribute the loads evenly over the supporting walls • Bedded in cement mortar on top of load-bearing wall
- 13. Eaves • Bottom portionof the roof overhanging the wall Verge • Roof covering overhangs the gable end Purlin • Horizontal roof members which give intermediate support to rafters • Act as beam, reducing the span of rafters & enabling economic section to be used
- 15. 1.2.3 FLAT ROOF • For large / complicated shaped building • Low-pitched roof, 10 degree or less • Simplest form: timber flat covered with impervious material to prevent rain penetration • Suitable for spans up to 4000mm • Spacing of roof joists is controlled by the width of decking material / ceiling board • To fall in 1 direction towards a gutter / outlet by fixing fittings to the top of the joist
- 17. Advantages of FlatRoof • Less material is being used than in a sloped roof • The rooftop is potentially useful as a terrace or sleeping porch • Potentially pleasing appearance • Easier to build than a sloped roof Disadvantages of Flat Roof • Limited capacity for insulation • Contrast in style with other buildings in the vicinity • Pools of water will collect on the surface unless it is properly designed & constructed • Little / no space to accommodate services
- 19. 1.3 MATERIALS FORROOFING Pitched Roof Tiles Slates Shingles (Wood tiling) Sheet Coverings Flat Roof Asphalt Aluminium Sheeting Zinc Sheeting Copper Sheeting
- 20. 1.3.1 TILING • Clay& concrete to wide range of design & colour • Pitches from 15 to45 degree • Pitch of a tile always less than pitch of the rafters • Laid in overlapping course • Water is shed off the surface of 1tile on to the exposed surface of the tile in the next course • Two types: A) Plain Tiling B) Single Lap Tiles
- 22. 1.3.1.1 PLAIN TILES • Double-lap principle • Size: 265x165x12mm • Under-eaves & top-course tiles: 215mm long • Tile-and-a-half tiles for verges: 248mm wide • Each tile has 2nibs for hanging over battens & 2 holes for nails near its head • Nailed with 38mm nails of Al alloy, copper/ c/c every 4th/5th course & at eaves, top course & verges • Can be handmade/ machine-pressed clay • Handmade: wide variation in colour,texture & shape; should not be laid on a roof of <45 degree • Machine-pressed: harder, denser more uniform in shape; can be laid to a min. pitch of 35 degree
- 25. 1.3.1.2 SINGLE LAPTILE • Laid with overlapping side joints toa min. pitch of 35 degree • Each tile overlaps the head of the tile in the course below • Side lap’s dimension is fixed by the design of tiles • Common types: Italian, Spanish, double Roman & pantiles • Adv: Lighter & permit a flatter slope of roof as they are in larger sizes & the actual inclination of the tiles is greater • Disadv: difficult to replace
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- 28. 1.3.2 SLATES • Naturallydense material, split into thin sheets • Every slate should be nailed twice • Laid to a min pitch of 25 degree • Centre nailing is used to overcome the problem of vibration caused by wind & tending to snap the slate at the fixing if nailed at the head
- 31. 1.3.3 ASPHALT FLATROOF • Consists of an aggregate with a bituminous binder, which is cast into blocks ready for reheating on site • Thickness & number of coats depend on surface type & substructure • Laying to a. horizontal surface: up to 10 degree pitch b. Sloping surface:10 to45 degree pitch c. Vertical surface: over 45 degree pitch • Horizontal surface should have 2 coats, breaking the joint & build-up to a min total thickness of 20mm • Vertical & sloping surface requires 3 coats, build up to a 20mm total thickness • Can be laid to falls so that the run-off of water is rapid & efficient
- 35. 1.3.4 ZINC SHEETING • A cheaper alternative to lead but has a shorter life • Not suitable for use in heavy industrial area • Does not creep, light &ductile • Normally 2500x1000mm with a min thickness of 0.80mm • Batten rolls to provide joints running with the fall of roof, about 985mm centres
- 37. 1.3.5 ALUMINIUM SHEETING • Thickness is often 0.80mm • Method of fixing is using batten rolls • Strength of aluminium is increased by the addition of alloy • Does not require protective treatment • Alternative is stainless steel sheeting
- 38. 1.4 ROOF SUPPORT Single Roof Collar Roof Couple Roof Double Roof Trussed Roof KingPost Queen Post Mansard Truss
- 39. 1.4.1 SINGLE ROOFS • Rafters are supported at the ends only • Simplest form: lean-to roof • 1 wall is carried up to a higher level than the other & rafters bridge the space between • Suitable for outbuildings & garages with span x< 2.50m • Upper ends of rafter supported by a ridge board plug to wall / plate
- 40. 1.4.1.1 COUPLE ROOF • Rafter supported by a ridge board & wall plates • No tie; rafters exert an outward thrust on the walls • Not be used for spans exceeding 5.00m • Improvement: couple close roof -nail ceiling joist to each pair of rafters; span increased up to 4.00m
- 41. 1.4.1.2 COLLAR ROOF • For span up to 5.00m • Each pair of rafters is framed up with a horizontal collar (collar tie), which should not be placed higher than of the vertical height from wall plate to ridge • Valuable when additional headroom is needed
- 43. 1.4.2 DOUBLE ROOF • When span exceeds 5.00m • Purlins are used at about 3.00m centre to give intermediate support to rafters • Purlins supported by struts • Collar is provided at each 4thpair of rafter • For larger span, hangers at every 4thrafter with connections to purlin & ceiling binder, which is nailed to ceiling joists • Sizes of ceiling joists, binders, rafters & purlins depends on dead load to be carried, strength of timber, span & spacing of members
- 45. 1.4.3 TRUSSED ROOF • Used over large span: > 6.00m • Trusses are structurally designed frames based on triangle principle, serve to carry purlins • Trusses are spaced at 1800mm centre with the space between being filled by common rafters
- 46. 1.4.3.1 KING POSTTRUSS • For spans of 6.00 –9.00m • A triangular frame which support the ridge & purlins, spanned from truss to truss & carried common rafter & roof covering • Roof load transmitted through principal rafters to wall below • Principal rafters were bolted to a tie beam to prevent them spreading under load • Strut to prevent sagging
- 48. 1.4.3.2 QUEEN POSTTRUSS • Spans from 9.00 –12.75m • Similar to king post but it has 2 vertical post, strutted apart at their heads by a straining beam • Principal rafters are supported by 2 purlins • Feet of queen post are held in position by tenons, straps & staining sill
- 50. 1.4.3.3 MANSARD TRUSS • Incorporate king & queen post truss • Enable accommodation to be provided in roof space • Members of roof trusses are arranged so that their centre lines intersected joints
- 52. TUTORIAL 5 • Sketch thetypical construction terminology of a pitched roof together with its functions. Requirements: You should sketch the roof in an A4 paper and write its function beside the labels of the roof. (Individual)