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  • 1. RoofsEnclosure and horizontal structure Royal Agricultural College
  • 2. Prefabrication: light, dry, fast, flexible Royal Agricultural College
  • 3. What goes on top? ? Royal Agricultural College
  • 4. What goes on top? ? The roof Royal Agricultural College
  • 5. What does a roof do?• Two fundamental functions – Enclosure: separation of interior from exterior – Structure: span horizontally across interior spaces• Several secondary functions – Insulation: control of heat transfer – Service distribution: pipes and wires – Storage space: we all want lofts Royal Agricultural College
  • 6. Structure first Royal Agricultural College
  • 7. Structure first A dome or arched vault. Pushes walls out Royal Agricultural College
  • 8. Structure first A dome or arched vault. Pushes wallsA column outsupported “tent”.Very difficult tobuild Royal Agricultural College
  • 9. Structure first A dome or arched vault. Pushes wallsA column outsupported “tent”.Very difficult to Compressed air supporting abuild “skin”. Insulation very difficult Royal Agricultural College
  • 10. Most common domestic solutions Triangulated truss Self-supporting beamTimber is the most common structural roofing material Royal Agricultural College
  • 11. Naming of parts of a simple pitched roofridge slope hip verge valley eavesgable Roof covering wall plate Royal facia Agricultural College soffit
  • 12. Rafters and ties create a strong triangular structure Rafters Ties (or ceiling joists) But they can sag… Royal Agricultural College
  • 13. Rafters and ties create a strong triangular structure But they can sag… Royal Agricultural College
  • 14. Basic solution to sag: hangers and struts 1 Hanger, securedThe maze of hangers at the ridge, holdsand struts is called up centre of ties.the web Under tension 2 Struts, supported by hanger, prop up rafters. Under compression Royal Agricultural College
  • 15. Basic shapes of prefabricated “Trussed rafters” These are built from Fink truss is the small section softwood, most common typically 100 x 50mm Room in roof: not fully Royal Agricultural triangulated, so timbers have CollegeImage source www.tra.org.uk to be larger
  • 16. Joints: Butt joints with gang-nail plate connectors on each side Nail plate hydraulically squeezed onto both sides of joint Plates formed from sheet Royal Agricultural galvanised steel College
  • 17. Jointing of trussed raftersGang nail plates used on all joints. No otherconnection between timbers. Even the main tiemay be in two pieces with a joint Royal Agricultural College
  • 18. View of gang-nailed roof structure Royal Agricultural College
  • 19. Trussed rafters prefabricated and delivered to site Royal Agricultural College
  • 20. Trussed rafters are weak until built into position and must be braced Royal Agricultural CollegeImage source www.tra.org.uk
  • 21. Network of small timbers build into a 3-dimensional structure Royal Agricultural College
  • 22. Complex roof shapes can be built using prefab. units Royal Agricultural College Image source www.tra.org.uk
  • 23. At the eaves Essential that the roof structure is physically tied down to the walls. The roof will blow off otherwise Royal Agricultural College
  • 24. That’s a trussed rafter roof, what about a flat roof? Royal Agricultural College
  • 25. Flat roofs: how do they stay up?• Flat roofs built from beams of materials which are stiff and can take both compression and tension• Steel is very good but most domestic construction uses timber 150 - 300 mm 50 - Royal 75mm Agricultural Max length for solid timber approx 4m College
  • 26. Joists at 600centres Wall plates (100X50) bolted or strapped to the wall Roof beams at 600mm Royal Agricultural centres are called joists College
  • 27. Trimmer Doubled joist Forming openings Royal Agricultural College
  • 28. RoyalAgricultural College
  • 29. Roof decking Royal Agricultural College
  • 30. Roof decking Royal Agricultural College
  • 31. Roof decking Decking must be strong & water resistant. Plywood is ideal, Royal never chipboard Agricultural College
  • 32. Basics of a flat roof with a fallDecking forms base for covering Royal Firring piece on each Agricultural joist to create fall College
  • 33. Flat timber roof eaves Firring piece on each joistfacia Roof deck and finish to create fall to gutter Roof joists at 600mm centressoffit 100X75 wall plate Stainless steel wall plate straps at 1200 centres Royal Agricultural College
  • 34. Deep beams• There is a limit to the size of a piece of timber.• Deep wooden beams can be built up by laminating (gluing together multiple thin layers) small pieces of timber• Laminated timber is actually stronger than natural timber of the same size. Royal Agricultural College
  • 35. Covering the roofThe structure is complete. Now you need tokeep the rain out and the heat in Royal Agricultural College
  • 36. References• CHUDLEY, R. GREENO, R. (2005). Construction technology. 4th ed. Pearson Education. CHUDLEY, R. GREENO, R. (2006). Building construction handbook. 6th ed. Butterworth-Heinemann.• Trussed rafter association http://www.tra.org.uk• Glue laminated timber association http://www.glulam.co.uk Royal Agricultural College