1. ROOFING
BCGCA3007B

2. Types of Roofs

3. Types of Roofs

4. Types of Roofs

5. Problem No1
Calculate Underside of Beams

6. Problem No1
Calculate Underside of Beams

18. Exercise 2 – Draw in Hips & Valleys

19. Exercise 2

25. Review Principles of Roofing
Ridges are Level
Rafters run at 90⁰ to Wall Plate
Hips & Valleys bisect all internal & external Corners
Roof members are set out along centerlines

27. Common Rafter Main Roofing Member Calculated same method as Gable
Spaced 450mm to 600mm for Tiled Roofs 600mm to 900mm for Sheet Roof
Cut using a Pattern Rafter

29. Centering Rafter Layout Roofs are Set out by Centreline
Centring Rafters
Centering Rafters Set back by Half Span

30. Centering Rafter Layout
Half Span
Centering Rafters Set back by Half Span

31. Ridge
Used to centre Rafters
Length = Length – span + Rafter Thickness

32. Determine Ridge Length

33. Crown End Rafters Cut & Fitted Against Ridge Act as Opposing Braces
Similar to Common Rafter
Half Rafter is Deducted

34. Crown End Rafter Layout What is the Crown End Rafter Centreline Span?
Crown End Rafters

35. Crown End Rafter Layout
Ridge 140 x19 Rafter 90 x 45
Crown End Rafters
CL Span is Half span
CL Span is Half span

36. Crown End Rafter Layout What is the run of Centering Rafter & Crown End Rafter
Ridge 140 x19 Rafter 90 x 45
Crown End Rafters
CL Span is Half span
CL Span is Half span

37. Crown End Rafter Layout What is the run of Centering Rafter & Crown End Rafter
Centering Rafters
Crown End Rafters
Ridge
Hip Rafters

38. Crown End Rafter Run deduct Half Centering Rafter
Crown End Rafter Layout What is the run of Centering Rafter & Crown End Rafter
Ridge 140 x19 Rafter 90 x 45
Centering Rafter Run
Deduct Half Ridge
Crown End Rafter Run deduct Half Centering Rafter

39. Crown End & Centering Rafter
Run Crown End Rafter = Half Span – Half Centering Rafter Width
Run Centering Rafter = Half Span – Half Ridge Width

41. Hip Rafter
Runs From Corner to Intersection Crown End & Centering Rafter - Centerline
Hips Bisect Corners
Fixing and Locating of Creepers
Distance above Birdsmouth is same as common rafters

42. Hip Rafter Layout Roofs are Set out by Centerline
Bisects Corner
Hip in Plan

43. Hip Rafter
Span of Hip

44. Hip Rafter
Hip Run
Hip Span

45. Hip Rafter
Hip Run
Hip Span

46. Hip Rafter
Hip Run
Hip Span

47. Hip Rafter
Corner Trimmed to allow a better fit
Hip Run
Hip Span

48. Hip Rafter

49. Hip Rafter Layout Roofs are Set out by Centerline
Bisects Corner
Determine Centreline Span of Hip

50. Centreline Span of Hip (Z)
X = Half span = 2070
Z = √(x2) + (x2) = √(20702) + (20702)
Z = 2927
X = Half span = 2070
Z = Half span x √2
Z = 2927

51. Centreline Span of Hip (Z)
X = Half span = 2070
Z = √(x2) + (x2) = √(20702) + (20702)
Z = 2927
X = Half span = 2070
Z = Half span x √2
Z = 2927

52. Centreline Length of Hip Mathematically
Methods
Pythagoras
Hip Centreline Length per Meter of Common Rafter Run
Full Length Calculation

53. Hip by Pythagoras Pitch 25⁰ Step 1 – Calculate Roof Rise
Rise = Tan 25⁰ x 2070
= 965mm

54. Hip by Pythagoras Pitch 25⁰ Hip Rise Must Be The Same
Step 1 – Calculate Roof Rise
Rise = Tan 25⁰ x 2070
= 965mm

55. Hip by Pythagoras Pitch 25⁰ Rise 965mm
Hip Rise Must Be The Same as the rest of the roof
Step 1 – Calculate Roof Rise
Rise = Tan 25⁰ x 2070
= 965mm
Hip Centreline Length = √(Hip Span² + Rise²)
= √(2927² + 965²)
= 3082mm
What is the Hip Pitch ?

56. Hip by Pythagoras Pitch 25⁰ Rise = 965mm Hip CL = 3082
What is the Hip Pitch ?
Using Tan
Tan Pitch = Rise/ Hip Span
Tan Pitch = 965/2927
Pitch = 18.25⁰
Using Cos
Cos Pitch = Hip Span/ Hip CL Length
Cos Pitch = 2927/3082

57. Centreline Length of Hip Mathematically
Methods
Pythagoras
Hip Centreline Length per Meter of Common Rafter Run
Full Length Calculation

58. Given Rise
= 577 per metre
From Gable Roof Lessons
We Know That for the above Roof the Rafter Length per meter can be calculated as follows
Rafter per meter run = √(1² ²) =

59. Given Rise
= 577 per metre
From Gable Roof Lessons
We Know That for the above Roof the Rafter Length per meter can be calculated as follows
Rafter per meter run = √(1² ²) =

60. Given Rise
= 577 per metre
We learnt previously that for every run of the common rafter the hip run is 1.414

61. Given Rise
= 577 per metre
We learnt previously that for every 1meter run of the common rafter the hip run is 1.414

62. Given Rise
= 577 per metre
Using Pythagoras we determine the above triangle
Hip per meter of Common Rafter Run = √(1.414² ²)
= 1.527

63. Given Rise
= 577 per metre
Using Pythagoras we determine the above triangle
Hip per meter of Common Rafter Run = √(√2² ²)
= √( ²)
= √(2.333)
= 1.527
We can now say that at this given rise per meter, for every meter of run of the common rafter the hip length will be 1527mm

64. Given Rise
= 577 per metre
Using Pythagoras we determine the above triangle
Hip per meter of Common Rafter Run = √(√2² ²)
= √( ²)
= √(2.333)
= 1.527
Therefore Halfspan = 2.070
CL Hip Rafter = x 1.527 =

65. Pitch = 30⁰
Lets extend this principle
Roof Pitch = 30⁰
Tan 30⁰ = 0.577

66. Pitch = 30⁰
This Triangle represents the Common Rafter Pitch
Which by similar triangles we can transfer to our steel square
Lets extend this principle
Roof Pitch = 30⁰
Tan 30⁰ = 0.577
This Brings Our Triangle from The Previous Example Back

67. Pitch = 30⁰
We learnt previously that for every 1meter run of the common rafter the hip run is 1.414

68. Pitch = 30⁰
Using Pythagoras we determine the above triangle
Hip per meter of Common Rafter Run = √(√2² x ²)
= √( ²)
= √(2.333)
= 1.527
Therefore for every meter of Common Rafter run at 30⁰
The Hip Centreline Length = 1.527

69. Calculate Hip Length per meter of Common Rafter Run

70. Calculate Hip Length per meter of Common Rafter Run