Roof framing

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Home inspection information regarding roof
Sacramento, California home inspection information from
Full Circle Home Inspections
www.fullcirclehomeinspections.com

Published in: Real Estate

Roof framing

  1. 1. F u l l C i r c l e H o m e I Roof Framing n s p e c t i o n s A Quick Primer The National Association of Certified Home Inspectors www.NACHI.org Copyright 2006 The National Association of Certified Home Inspectors
  2. 2. F u l l Roof Framing C i r c l Roof types e H Gable – Most common, built with “common” rafters o m Hip – Provides overhang on all four sides e I Gambrel – Provides more space on second floor n s p Mansard – Combination of Hip and Gambrel e c t Shed- Frequently used to attach one structure to another i o n s Copyright 2006 The National Association of Certified Home Inspectors
  3. 3. F u l l Roof Framing C i r c l e Definitions H o m Common rafter – Runs e from top plate to I n ridgeboard of a gable s p roof e c t i Hip rafter – Runs from o n corner of top plates to s ridgeboard on a hip roof Jack rafter – any rafter which does not run the full length from plate to ridge ( e.g. – Hip jack, Valley jack) Copyright 2006 The National Association of Certified Home Inspectors
  4. 4. F u l l Roof Framing C i r c l e H Roof Geometry Definitions o m Span – Measurement from e outside of wall to outside of I opposite wall n s Run – One half of span (for p e symmetric roofs) c t Rise – The total vertical i o distance that the roof projects n s above the top plate Slope – The rise divided by the run, always given in terms of 12” of run (e.g. 3 on 12 written 3/12) Pitch – The rise over the span Copyright 2006 The National Association of Certified Home Inspectors
  5. 5. F u l l Roof Framing C i r c l e Overhang – The section H of the rafter extending o m past the edge of the wall e I Projection – The n s horizontal distance that p e the overhang covers c t i o Rafter tail cuts – Cuts n s made to form the overhang Birdsmouth – Cuts made to sit on the top plate Ridge cut – Cut made to attach to the ridgeboard Copyright 2006 The National Association of Certified Home Inspectors
  6. 6. F u l l Roof Framing C i r c l e H o Rafters vs. Trusses m e Rafters used frequently I for remodeling, for n s cathedral ceilings, for p e shed roof additions, for c t full 2nd floor storage, and i o n spans up to 24’ s Trusses used in most new construction, for spans 24’-60’, and most commonly for lower sloped roofs Copyright 2006 The National Association of Certified Home Inspectors
  7. 7. F u l l Roof Framing C i r c l e H Sizing Rafters – Rafter o m size (like span tables for e floor joists) depends on I n s spacing, species, load, p e c and span. Sizing of t i o rafters typically based n s on snow load in Northeast. The specific loads come from the International building code Copyright 2006 The National Association of Certified Home Inspectors
  8. 8. F u l l Roof Framing C i r c l e H o Determining rafter m lengths – There are two e I distances needed for n s p rafter layout e c Ridge cut to birdsmouth t i o n Ridge cut to tail cut s Determining rafter length can be done using calculator, builder’s calculator, or look-up tables Copyright 2006 The National Association of Certified Home Inspectors
  9. 9. F u l l Roof Framing C i r c l e To calculate the rafter H o length, the “rafter m e square” contains tables I n that are inscribed in the s p square. The carpenter e c t can use this information i o n to avoid the need to s work with trigonometric functions. The square includes info for common rafters, hips, valleys and jacks. Copyright 2006 The National Association of Certified Home Inspectors
  10. 10. F u l l Roof Framing C i r c l e H o For example: m e I n s p e c t i o n s Copyright 2006 The National Association of Certified Home Inspectors
  11. 11. F u l l Roof Framing C i r c l e H o m e I n s p e c t i o n s Copyright 2006 The National Association of Certified Home Inspectors
  12. 12. F u l l Roof Framing C i r c l e H o Hips and Valley rafters m e can also be calculated I n and laid out using the s p rafter square, with some e c t important differences; i o n s The unit run is 17, not 12 The ridge, birdsmouth, and tail need cheek cuts, or some modification or the top surface needs to be beveled Copyright 2006 The National Association of Certified Home Inspectors
  13. 13. F u l l Roof Framing C i r c l e H o The Hip (or Valley) m e rafter forms a I n diagonal on the roof, s p and the length of that e c t diagonal is 17” for i o n each 12” of run of the s common rafters. Copyright 2006 The National Association of Certified Home Inspectors
  14. 14. F u l l Roof Framing C i r c l e H o The ridge cut is m e modified to fit into the I n space between the s p common rafters e c t i o n s Copyright 2006 The National Association of Certified Home Inspectors
  15. 15. F u l l Roof Framing C i r c l e H o The Birds mouth must be m dropped, or the top of the e I rafter beveled to account for n s the centerline being lower p e than the edges of the rafter c t i o n s Copyright 2006 The National Association of Certified Home Inspectors
  16. 16. F u l l Roof Framing C i r c l e H o The tail cuts will be m e beveled for solid nailing I n at the outside corner. s p For Hip rafters this is an e c t outside corner, and for i o n valley rafters this is an s inside corner. Copyright 2006 The National Association of Certified Home Inspectors
  17. 17. F u l l Roof Framing C i r c l e H o m e I n s p e c t i o n s Copyright 2006 The National Association of Certified Home Inspectors
  18. 18. F u l l Roof Framing C i r c l e H o m e I n s p e c t i o n s Copyright 2006 The National Association of Certified Home Inspectors
  19. 19. F u l l Roof Framing C i r c l e Jack rafters have a H o m cheek cut where they e meet the hip or valley. I n s Each one is shorter than p e the last by a “common c t i o difference”. n s Copyright 2006 The National Association of Certified Home Inspectors
  20. 20. F u l l Roof Framing C i r c l e H The concept of o m “common difference” e I will also be applied n s p when cutting gable end e c studs. t i o n s Copyright 2006 The National Association of Certified Home Inspectors
  21. 21. F u l l Roof Framing C i r c l e H o m e I n s p e c t i o n s Copyright 2006 The National Association of Certified Home Inspectors
  22. 22. F u l l Roof Framing C i r c l e Dormers – Most H o dormers are either shed m e or gable dormers. They I n are framed with s p common rafters. e c t i o n s Copyright 2006 The National Association of Certified Home Inspectors
  23. 23. F u l l Roof Framing C i r c l e Where shed or gable H o dormers meet the main m e roof, the rafters must be I n cut to create either a s p valley or break. e c t i o n s Copyright 2006 The National Association of Certified Home Inspectors
  24. 24. F u l l Roof Framing C i r c l e H o Gable end overhangs – m e Both rafter and truss I n roofs commonly use s p gable end overhangs. e c t However the overhangs i o n are framed differently s for trusses than for rafters. Copyright 2006 The National Association of Certified Home Inspectors
  25. 25. F u l l Roof Framing C i r c l e The vast majority of H o new construction uses m e trusses for the roof I n framing. Each truss is s p e designed for the c t i individual o n s characteristics of the job, and delivered to the site ready to be erected. It is very rare that anyone site builds a truss today. Copyright 2006 The National Association of Certified Home Inspectors
  26. 26. F u l l Roof Framing C i r c l e H There are a number of o m important points in building e a truss roof: I n s p Proper handling e c Proper lifting and setting t i o n Proper temporary bracing s Proper permanent bracing These are explained in notes will be found on the paper that comes with the trusses Copyright 2006 The National Association of Certified Home Inspectors
  27. 27. F u l l Roof Framing C i r c l e H o Proper Handling – m e Trusses are made of I n small dimension lumber s p connected by metal e c t plates. Side loading, i o n heat, shock loading can s damage metal plates and greatly weaken truss. Copyright 2006 The National Association of Certified Home Inspectors
  28. 28. F u l l Roof Framing C i r c l e H Proper lifting and o m setting – A truss e erection plan will show I n s the location of each p e c numbered truss. t i o n s Copyright 2006 The National Association of Certified Home Inspectors
  29. 29. F u l l Roof Framing C i r c l e H o Proper temporary m e bracing – The most I n common cause of truss s p collapse is insufficient e c t or improper temporary i o n bracing. Temporary s bracing stays in place until the roof is sheathed and the permanent bracing is installed. Copyright 2006 The National Association of Certified Home Inspectors
  30. 30. F u l l Roof Framing C i r c l e H o The result of not m e bracing trusses. I n 47 MPH wind speed for s p e a period of 1 minute. c t i o n s Copyright 2006 The National Association of Certified Home Inspectors
  31. 31. F u l l Roof Framing C i r c l e Permanent Bracing – H o This is usually shown m on the truss erection e I diagram. Compression n s p members will buckle e c easily (and truss will not t i o develop its design n s strength) if not properly braced. This can be done with continuous lateral or individual T bracing Copyright 2006 The National Association of Certified Home Inspectors

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