RoofsEnclosure and horizontal structure                                          Royal                                    ...
Prefabrication: light, dry,      fast, flexible                                   Royal                              Agric...
What goes on top?     ?                         Royal                    Agricultural                       College
What goes on top?     ?  The roof                         Royal                    Agricultural                       Coll...
What does a roof do?• Two fundamental functions  – Enclosure: separation of interior from    exterior  – Structure: span h...
Structure first                       Royal                  Agricultural                     College
Structure first            A dome or            arched vault.            Pushes walls            out                      ...
Structure first                                A dome or                                arched vault.                     ...
Structure first                                      A dome or                                      arched vault.         ...
Most common domestic               solutions   Triangulated truss          Self-supporting beamTimber is the most common s...
Naming of parts of a simple               pitched roofridge                 slope           hip                        ver...
Rafters and ties create a strong      triangular structure                            Rafters                           Ti...
Rafters and ties create a strong      triangular structure       But they can sag…                                        ...
Basic solution to sag: hangers              and struts                                      1 Hanger, securedThe maze of h...
Basic shapes of prefabricated       “Trussed rafters”  These are built from                      Fink truss is the  small ...
Joints: Butt joints with gang-nail plate connectors on each side             Nail plate             hydraulically         ...
Jointing of trussed raftersGang nail plates used on all joints. No otherconnection between timbers. Even the main tiemay b...
View of gang-nailed roof structure                                          Royal                                     Agri...
Trussed rafters prefabricated    and delivered to site                                     Royal                          ...
Trussed rafters are weak until built into position and must be braced                                             Royal   ...
Network of small timbers build into    a 3-dimensional structure                                           Royal          ...
Complex roof shapes can be  built using prefab. units                                                 Royal               ...
At the eaves       Essential that the roof       structure is physically tied       down to the walls. The roof       will...
That’s a trussed rafter roof,  what about a flat roof?                                     Royal                          ...
Flat roofs: how do they stay up?• Flat roofs built from beams of  materials which are stiff and can  take both compression...
Joists at 600centres                              Wall plates                              (100X50) bolted or             ...
Trimmer                    Doubled joist Forming openings                                         Royal                   ...
RoyalAgricultural   College
Roof decking                    Royal               Agricultural                  College
Roof decking                    Royal               Agricultural                  College
Roof decking               Decking must be               strong & water               resistant.               Plywood is ...
Basics of a flat roof with a fallDecking forms base for covering                                                          ...
Flat timber roof eaves                                        Firring piece on each joistfacia         Roof deck and finis...
Deep beams• There is a limit to the size of a piece of timber.• Deep wooden beams can be built up by  laminating (gluing t...
Covering the roofThe structure is complete. Now you need tokeep the rain out and the heat in                 Royal        ...
References• CHUDLEY, R. GREENO, R. (2005).  Construction technology. 4th ed. Pearson  Education.  CHUDLEY, R. GREENO, R. (...
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  1. 1. RoofsEnclosure and horizontal structure Royal Agricultural College
  2. 2. Prefabrication: light, dry, fast, flexible Royal Agricultural College
  3. 3. What goes on top? ? Royal Agricultural College
  4. 4. What goes on top? ? The roof Royal Agricultural College
  5. 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. 6. Structure first Royal Agricultural College
  7. 7. Structure first A dome or arched vault. Pushes walls out Royal Agricultural College
  8. 8. Structure first A dome or arched vault. Pushes wallsA column outsupported “tent”.Very difficult tobuild Royal Agricultural College
  9. 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. 10. Most common domestic solutions Triangulated truss Self-supporting beamTimber is the most common structural roofing material Royal Agricultural College
  11. 11. Naming of parts of a simple pitched roofridge slope hip verge valley eavesgable Roof covering wall plate Royal facia Agricultural College soffit
  12. 12. Rafters and ties create a strong triangular structure Rafters Ties (or ceiling joists) But they can sag… Royal Agricultural College
  13. 13. Rafters and ties create a strong triangular structure But they can sag… Royal Agricultural College
  14. 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. 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. 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. 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. 18. View of gang-nailed roof structure Royal Agricultural College
  19. 19. Trussed rafters prefabricated and delivered to site Royal Agricultural College
  20. 20. Trussed rafters are weak until built into position and must be braced Royal Agricultural CollegeImage source www.tra.org.uk
  21. 21. Network of small timbers build into a 3-dimensional structure Royal Agricultural College
  22. 22. Complex roof shapes can be built using prefab. units Royal Agricultural College Image source www.tra.org.uk
  23. 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. 24. That’s a trussed rafter roof, what about a flat roof? Royal Agricultural College
  25. 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. 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. 27. Trimmer Doubled joist Forming openings Royal Agricultural College
  28. 28. RoyalAgricultural College
  29. 29. Roof decking Royal Agricultural College
  30. 30. Roof decking Royal Agricultural College
  31. 31. Roof decking Decking must be strong & water resistant. Plywood is ideal, Royal never chipboard Agricultural College
  32. 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. 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. 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. 35. Covering the roofThe structure is complete. Now you need tokeep the rain out and the heat in Royal Agricultural College
  36. 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

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