Presentation is loading. Please wait.

Presentation is loading. Please wait.

Copyright 2006 The National Association of Certified Home Inspectors Roof Framing A Quick Primer The National Association of Certified Home Inspectors.

Similar presentations


Presentation on theme: "Copyright 2006 The National Association of Certified Home Inspectors Roof Framing A Quick Primer The National Association of Certified Home Inspectors."— Presentation transcript:

1 Copyright 2006 The National Association of Certified Home Inspectors Roof Framing A Quick Primer The National Association of Certified Home Inspectors Home Inspectorswww.NACHI.org

2 Copyright 2006 The National Association of Certified Home Inspectors Roof Framing Roof types Roof types Gable – Most common, built with common rafters Gable – Most common, built with common rafters Hip – Provides overhang on all four sides Hip – Provides overhang on all four sides Gambrel – Provides more space on second floor Gambrel – Provides more space on second floor Mansard – Combination of Hip and Gambrel Mansard – Combination of Hip and Gambrel Shed- Frequently used to attach one structure to another Shed- Frequently used to attach one structure to another

3 Copyright 2006 The National Association of Certified Home Inspectors Definitions Definitions Common rafter – Runs from top plate to ridgeboard of a gable roof Common rafter – Runs from top plate to ridgeboard of a gable roof Hip rafter – Runs from corner of top plates to ridgeboard on a hip roof Hip rafter – Runs from corner of top plates to 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) Jack rafter – any rafter which does not run the full length from plate to ridge ( e.g. – Hip jack, Valley jack) Roof Framing

4 Copyright 2006 The National Association of Certified Home Inspectors Roof Geometry Definitions Roof Geometry Definitions Span – Measurement from outside of wall to outside of opposite wall Span – Measurement from outside of wall to outside of opposite wall Run – One half of span (for symmetric roofs) Run – One half of span (for symmetric roofs) Rise – The total vertical distance that the roof projects above the top plate Rise – The total vertical distance that the roof projects 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) 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 Pitch – The rise over the span Roof Framing

5 Copyright 2006 The National Association of Certified Home Inspectors Overhang – The section of the rafter extending past the edge of the wall Overhang – The section of the rafter extending past the edge of the wall Projection – The horizontal distance that the overhang covers Projection – The horizontal distance that the overhang covers Rafter tail cuts – Cuts made to form the overhang Rafter tail cuts – Cuts made to form the overhang Birdsmouth – Cuts made to sit on the top plate Birdsmouth – Cuts made to sit on the top plate Ridge cut – Cut made to attach to the ridgeboard Ridge cut – Cut made to attach to the ridgeboard Roof Framing

6 Copyright 2006 The National Association of Certified Home Inspectors Rafters vs. Trusses Rafters vs. Trusses Rafters used frequently for remodeling, for cathedral ceilings, for shed roof additions, for full 2 nd floor storage, and spans up to 24 Rafters used frequently for remodeling, for cathedral ceilings, for shed roof additions, for full 2 nd floor storage, and spans up to 24 Trusses used in most new construction, for spans 24-60, and most commonly for lower sloped roofs Trusses used in most new construction, for spans 24-60, and most commonly for lower sloped roofs Roof Framing

7 Copyright 2006 The National Association of Certified Home Inspectors Sizing Rafters – Rafter size (like span tables for floor joists) depends on spacing, species, load, and span. Sizing of rafters typically based on snow load in Northeast. The specific loads come from the International building code Sizing Rafters – Rafter size (like span tables for floor joists) depends on spacing, species, load, and span. Sizing of rafters typically based on snow load in Northeast. The specific loads come from the International building code Roof Framing

8 Copyright 2006 The National Association of Certified Home Inspectors Determining rafter lengths – There are two distances needed for rafter layout Determining rafter lengths – There are two distances needed for rafter layout Ridge cut to birdsmouth Ridge cut to birdsmouth Ridge cut to tail cut Ridge cut to tail cut Determining rafter length can be done using calculator, builders calculator, or look-up tables Roof Framing

9 Copyright 2006 The National Association of Certified Home Inspectors To calculate the rafter length, the rafter square contains tables that are inscribed in the square. The carpenter can use this information to avoid the need to work with trigonometric functions. The square includes info for common rafters, hips, valleys and jacks. To calculate the rafter length, the rafter square contains tables that are inscribed in the square. The carpenter can use this information to avoid the need to work with trigonometric functions. The square includes info for common rafters, hips, valleys and jacks. Roof Framing

10 Copyright 2006 The National Association of Certified Home Inspectors For example: For example: Roof Framing

11 Copyright 2006 The National Association of Certified Home Inspectors Roof Framing

12 Copyright 2006 The National Association of Certified Home Inspectors Hips and Valley rafters can also be calculated and laid out using the rafter square, with some important differences; Hips and Valley rafters can also be calculated and laid out using the rafter square, with some important differences; The unit run is 17, not 12 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 The ridge, birdsmouth, and tail need cheek cuts, or some modification or the top surface needs to be beveled Roof Framing

13 Copyright 2006 The National Association of Certified Home Inspectors The Hip (or Valley) rafter forms a diagonal on the roof, and the length of that diagonal is 17 for each 12 of run of the common rafters. The Hip (or Valley) rafter forms a diagonal on the roof, and the length of that diagonal is 17 for each 12 of run of the common rafters. Roof Framing

14 Copyright 2006 The National Association of Certified Home Inspectors The ridge cut is modified to fit into the space between the common rafters The ridge cut is modified to fit into the space between the common rafters Roof Framing

15 Copyright 2006 The National Association of Certified Home Inspectors The Birds mouth must be dropped, or the top of the rafter beveled to account for the centerline being lower than the edges of the rafter The Birds mouth must be dropped, or the top of the rafter beveled to account for the centerline being lower than the edges of the rafter Roof Framing

16 Copyright 2006 The National Association of Certified Home Inspectors The tail cuts will be beveled for solid nailing at the outside corner. For Hip rafters this is an outside corner, and for valley rafters this is an inside corner. The tail cuts will be beveled for solid nailing at the outside corner. For Hip rafters this is an outside corner, and for valley rafters this is an inside corner. Roof Framing

17 Copyright 2006 The National Association of Certified Home Inspectors Roof Framing

18 Copyright 2006 The National Association of Certified Home Inspectors Roof Framing

19 Copyright 2006 The National Association of Certified Home Inspectors Jack rafters have a cheek cut where they meet the hip or valley. Each one is shorter than the last by a common difference. Jack rafters have a cheek cut where they meet the hip or valley. Each one is shorter than the last by a common difference. Roof Framing

20 Copyright 2006 The National Association of Certified Home Inspectors The concept of common difference will also be applied when cutting gable end studs. The concept of common difference will also be applied when cutting gable end studs. Roof Framing

21 Copyright 2006 The National Association of Certified Home Inspectors Roof Framing

22 Copyright 2006 The National Association of Certified Home Inspectors Dormers – Most dormers are either shed or gable dormers. They are framed with common rafters. Dormers – Most dormers are either shed or gable dormers. They are framed with common rafters. Roof Framing

23 Copyright 2006 The National Association of Certified Home Inspectors Where shed or gable dormers meet the main roof, the rafters must be cut to create either a valley or break. Where shed or gable dormers meet the main roof, the rafters must be cut to create either a valley or break. Roof Framing

24 Copyright 2006 The National Association of Certified Home Inspectors Gable end overhangs – Both rafter and truss roofs commonly use gable end overhangs. However the overhangs are framed differently for trusses than for rafters. Gable end overhangs – Both rafter and truss roofs commonly use gable end overhangs. However the overhangs are framed differently for trusses than for rafters. Roof Framing

25 Copyright 2006 The National Association of Certified Home Inspectors The vast majority of new construction uses trusses for the roof framing. Each truss is designed for the individual characteristics of the job, and delivered to the site ready to be erected. It is very rare that anyone site builds a truss today. The vast majority of new construction uses trusses for the roof framing. Each truss is designed for the individual characteristics of the job, and delivered to the site ready to be erected. It is very rare that anyone site builds a truss today. Roof Framing

26 Copyright 2006 The National Association of Certified Home Inspectors There are a number of important points in building a truss roof: There are a number of important points in building a truss roof: Proper handling Proper handling Proper lifting and setting Proper lifting and setting Proper temporary bracing Proper temporary bracing Proper permanent bracing Proper permanent bracing These are explained in notes will be found on the paper that comes with the trusses These are explained in notes will be found on the paper that comes with the trusses Roof Framing

27 Copyright 2006 The National Association of Certified Home Inspectors Proper Handling – Trusses are made of small dimension lumber connected by metal plates. Side loading, heat, shock loading can damage metal plates and greatly weaken truss. Proper Handling – Trusses are made of small dimension lumber connected by metal plates. Side loading, heat, shock loading can damage metal plates and greatly weaken truss. Roof Framing

28 Copyright 2006 The National Association of Certified Home Inspectors Proper lifting and setting – A truss erection plan will show the location of each numbered truss. Proper lifting and setting – A truss erection plan will show the location of each numbered truss. Roof Framing

29 Copyright 2006 The National Association of Certified Home Inspectors Proper temporary bracing – The most common cause of truss collapse is insufficient or improper temporary bracing. Temporary bracing stays in place until the roof is sheathed and the permanent bracing is installed. Proper temporary bracing – The most common cause of truss collapse is insufficient or improper temporary bracing. Temporary bracing stays in place until the roof is sheathed and the permanent bracing is installed. Roof Framing

30 Copyright 2006 The National Association of Certified Home Inspectors The result of not bracing trusses. The result of not bracing trusses. 47 MPH wind speed for a period of 1 minute. 47 MPH wind speed for a period of 1 minute. Roof Framing

31 Copyright 2006 The National Association of Certified Home Inspectors Permanent Bracing – This is usually shown on the truss erection diagram. Compression members will buckle easily (and truss will not develop its design strength) if not properly braced. This can be done with continuous lateral or individual T bracing Permanent Bracing – This is usually shown on the truss erection diagram. Compression members will buckle easily (and truss will not develop its design strength) if not properly braced. This can be done with continuous lateral or individual T bracing Roof Framing


Download ppt "Copyright 2006 The National Association of Certified Home Inspectors Roof Framing A Quick Primer The National Association of Certified Home Inspectors."

Similar presentations


Ads by Google