1. Roof Trusses
Created By M.S.Martin 11/04, reviewed 11/05, reviewed 11/07

2. Often used instead of pitched roofs

3. Not Always conventional shapes

4. What do you know about them ?
Types
Shapes / Limitations ?
What supports them ?
How are they joined ?

5. Definition / Design
A truss is a self contained frame, designed to transfer roof loads, typically to external walls
Most modern roofs can be adapted to a trussed system
Members are typically joined by gangnail plates

6. Types

7. Types continued

8. Types continued

10. Types – Standard truss

12. Types - other
There are many other types of trusses used in conventional roof shapes and we’ll look at them a little later
First we need to look at the components and how a standard truss works

13. Hand out – worksheet one
Identify the parts of a standard truss
Summarize in your own words, the truss components, use the terminology section of carp 15 text for reference

14. Components

15. Terminology – worksheet answers
Bottom chord – the horizontal member forming the base of the truss, which will also support the ceiling below
Top chord – the angled member at the top of the truss, in a standard truss this is where a rafter would be
Web – these are the internal members of the truss that help distribute the load to the external walls
Camber – An upward curvature built into the bottom chord to compensate for deflection

16. Terminology continued
Girder truss – A truss that supports other trusses or beams, differs in shape depending on where it is in the roof
Nail plates – the connectors made from a light gauge steel that join individual components of the truss
Gable end truss – the first truss at a gable end
Raking truss – a gable end truss altered to suit outriggers for a verge overhang

17. Terminology continued
Panel points – these are the connection points in a truss, (eg) where a web meets a top chord
Fish plate – an alternative bolted connection at a panel point
Load bearing walls – in a trussed roof these are still the support walls, but are typically the external walls

18. Truss panel points

20. Tension & Compression

21. Compression & Tension
When trying to understand how this works its easier to look at half the truss

22. Handout – Tension & Compression
Review handout to help understand how this process takes place

23. Parallel Chord trusses
Used where large raking or level spans are required to bridge intermediate support
They provide strength and versatility

24. Ground floor system

25. Alternative system

28. Roof Trusses We mainly come across trusses in roof systems
Now we’ll have a look at the factors concerning them

29. Camber – P12
Trusses are built with a slight camber in the bottom chord
This is designed to provide maximum calculated deflection

30. Minimum clearance
Under no circumstances should trusses be supported along their span
With a trussed roof, internal walls are merely partitions / non-load bearing
Minimum clearance is 12mm

31. Support & Connections
The structure supporting the trusses must be level & square
External walls are load bearing with trussed roofs
Or intermediate panel points for cantilevered trusses
Either support directly over studs or change top plate

32. Support continued Where not supported by studs
Use thicker top plate, or
Double plate

33. Connections to trusses
Trusses require either factory connectors or nail or bolted connections on site, some of these are –
Nail plates (gang nail)
Triple grippes
Truss saddles
Multi purpose anchors
Various bolted brackets
Joist hanger brackets
Wall brackets

34. Types of connections

35. Types of connections

36. Types of connections

37. Types of connections

41. Worksheet two
Handout
Answer questions on handout to review section on support and connections
Use your text book to assist you in your answers

42. Answers to worksheet two
Parallel chord trusses – used in ground floor, suspended floors and roofs
Camber – is there to provide maximum deflection when roof loads are placed upon them
Minimum clearance for internal non-load bearing walls – 12mm
Wall structure support – either directly over studs or change top plate to thicker or double one

43. Answers continued
Connection methods used in trussed roofing – nail plates, triple grips, truss saddles, multi-purpose anchors, bolted brackets, joist hanger brackets, wall brackets.

44. Answers continued
Changes for a cantilever
It changes here

45. Fixing to non load bearing walls

46. Lifting roof trusses
If lifting manually, you should always use support timbers to drag them up
If using a crane be careful to sling them correctly
The advantage of a crane, many trusses can be lifted at once

47. Lifting continued

50. Roof truss types
Its important to get familiar with the different types of trusses used in lieu conventional roof frames, some are –
Standard
Truncated
Jack truss
Hip truss
Girder truss
And more

51. Some typical roofs- handout

52. Roofs continued

53. Breakup – P28 text

54. Standard roof truss

55. Other types

56. Location of trusses

57. Review text Review text for other types of trusses. Saddle trusses
Girder trusses
Etc.
Review from P29

58. Bracing and Erection Review text book for bracing requirements P24
Alternate roof styles P27
Cantilever trusses P32
Erection procedures P38

59. New alternative from Mitek

60. Alternative wall bracing
Mitek (gang nail) also make a timber wall bracing system they call Posi – brace
Suitable for most timber framed houses

61. Worksheet three Answer questions to worksheet provided
Review text for answers
Then complete handout on roof shape and select types of roof trusses to use on the conventional shaped roof shown.

62. Answers to worksheet three
Fixing to internal walls – by way of purpose made L-brackets, also, depending on layout of walls under, blocks may also have to be incorporated
Types – standard, truncated, jack truss, girder, hip truss, truncated girder
Support for saddle truss – timber ledger
Typical bracing – speed bracing
Picture for roof layout on next slide