1. Construct Pitched Roofs (Simple)
BCGA3007B
Construct Pitched Roofs
(Simple)

2. Types of Roofs we will Cover
Coupled Roofs
Gable Roofs

3. Types of Roofs we will Cover
Non Coupled Roofs
Skillion Roofs
Lean to
Graded Battens

4. What is a Roof

5. Roof Structure Definitions

6. Roof Structure Definitions

7. Flat Roofing Pitch less than 1:11.5 or 5⁰
Ceilings usually directly fixed to underside.
Member Sizes Adjusted Accordingly
Usually Single Span, therefore large members
Due to low pitch roof coverings types are limited

8. Skillion Roofs Freestanding Wall at one end is higher
Walls parallel to rafters are tapered

9. Selecting Members What determines rafter spacing ?
Ceiling Linings – if direct fixing
Roof Batten Span
Required Rafter span
Roof Material Mass
Ceiling Mass – if direct fixing

10. Selecting Members

11. For types of roof we will cover today

12. Roof Battens Have Span Limits – it is not uncommon where ceilings are unlined to space rafters greater than 650 c to c. Note 70 x 35 will be unsuitable
Always Check Notes first to ensure it is suitable

13. Select Rafter Size Pitch 3° Rafters 600 c to c
Step 1 – Determine Rafter Span
Span is defined in AS
cl & as distance between points of full support
Note Horizontal Distance is called run
Span is also used to determine rafters length mathematically.
In this case it is measured differently and will be explained later

14. 190 x 45 with maximum overhang of 1550
Rafter Spacing
Read Notes
Roof Load

15. Methods to Calculate Rafter Length
Rise 1 in 20
Rafters 600 c to c
230
To Calculate Rafter Length we need to Determine the Run of the Rafter.
Forming the above triangle
Generally in this type of roof it will be from back of birdsmouth to back of birdsmouth

16. Methods to Calculate Rafter
Rise 1 in 20
Rafters 600 c to c
230
Rise = Every 20 meters, Rise of 1 meters
Rise per m = 1/20
= 0.05 x 4.6
Rise = 0.230
Use Pythagoras to Calculate Rafter Length
Rafter = √ ( )
= 4.606
To Determine Pitch
Pitch =230/ 4600
= 0.05
= Inv Tan 0.05
= 2.862°

17. Methods to Calculate Rafter
Rise 1 in 20
Rafters 600 c to c
230
If we are given the pitch = = 2.862°
Rafter = Run / Cos Pitch
Rafter = 4600/Cos = 2.862°
= 4600/0.9988
=4606

18. Complete Following

19. Answers

21. Alternative Set Out Length = 4606mm 230
Step 1 – Set out Rafter Length along one edge
Remember to allow for overhang
Step 2 – Extend Plumb Lines to other edge

22. Similar Triangles If all angles are the same the triangles are similar
All sides are increased by same magnitude

23. Similar Triangles

24. Basic Steel Square Demo
Roof Run = 4600
Roof Rise = 210
Ratio =210/4200
= 0.05
Square Run = 500mm
Rise = 500 x 0.05 = 25
Alternate Method – Using Similar Triangles
Roof Pitch = 3°
Tan 3⁰ x 1m =0.052m (Answer is always value for 1)
Remember angles stay the same in similar triangles
Rise for triangle half size =
= tan 3⁰ x 0.500m
= 0.026m or 26mm
Plumb Cut 3⁰ 1

28. Graded Batten Roof
Where direct fix ceiling is required to be level on flat roof
Fall is achieved with Battens

29. Constructing a Skillion Roof
Place End Rafters, allowing for soldier trims

30. Place Rafters at maximum 600 centres (580)
Provide Solid Blocking at 1800 centers max

31. Install Soldier Trims

32. Cut Overhangs & Install Verge Trims

33. Install Wall Blocking

34. Install Fascia

35. Kliplock
Minimum Pitch 1⁰

36. Trimdeck
Minimum Pitch 2⁰

37. Custom Orb Generally Known as Corrugated Iron
Minimum Pitch 5⁰
Not Suitable For Flat Roofs
Maximum Recommended Support Spacings
Type of Span
Thickness (mm) BMT
0.42
0.48
Roofs Single Span End Span Internal Span Unstiffened Eaves Overhang Stiffened Eaves Overhang
Walls Single Span End Span Internal Span Overhang