1. Octagonal Roof

2. Draw Crown Rafters
Set Back ½ Rafter Thickness
Walls are parallel

3. Draw & Bisect Crown End Rafter

4. Draw Tangents to the Crown Ends

5. Draw Top Plate

6. Clean Up Drawing

7. Clean Up Drawing
Angle Between Major Crown End & Centring Rafters = 90⁰

8. Clean Up Drawing
Angle Between Crown End Rafters = 45⁰

9. Clean Up Drawing
Angle Between Crowns Ends & Hips = 22.5⁰

10. Angles formed by the Roof
These angles are the same no matter the size of Roof as it is a Geometric Shape

11. Length Of Octagonal Ends
If the angle between the members is constant 22.5⁰
We can say in all cases, no matter the size of the roof
½ End = ½ Span x tan 22.5⁰
= ½ Span x (tan 22.5⁰ is always used)

12. Length Of Octagonal Ends
If the angle between the members is constant 22.5⁰
We can say in all cases, no matter the size of the roof
½ End = ½ Span x 0.414

13. Length Of Octagonal Ends
If the angle between the members is constant 22.5⁰
In all cases, we can say
Full End = ½ Span x x 2

14. Length Of Octagonal Ends
If the angle between the members is constant 22.5⁰
Also in all cases, the full end will be
Full End = ½ Span x 0.828

15. Length Of Octagonal Ends
These formulas are the same no matter the size of the Roof
½ End = ½ Span x 0.414
Full End = ½ Span x 0.828

16. Major Crown End Rafter
These formulas are the same no matter the size of the Roof
Calculating Centring rafters and Crown End Rafter use the same method as a normal hip roof

17. Major Crown End Rafter
These formulas are the same no matter the size of the Roof
Calculating Centring rafters and Crown End Rafter use the same method as a normal hip roof

18. Minor Crown End Rafters
These formulas are the same no matter the size of the Roof
Minor Crown End Rafters join in a similar manner to a hip rafter

19. Minor Crown End Rafters
These formulas are the same no matter the size of the Roof
Minor Crown End Rafters join in a similar manner to a hip rafter
The Plan run of the minor crown is reduced by ;
½ Centring Rafter x 1.414

20. Minor Crown End Rafters
These formulas are the same no matter the size of the Roof
Minor Crown End Rafters join in a similar manner to a hip rafter
Minor Crown = ½ Span x ½ C.R Thickness÷

21. Edge Bevel Minor Crown End Rafters
Plan Angle = 45⁰

22. Edge Bevel Minor Crown End Rafters Plan Angle

23. Edge Bevel Minor Crown End Rafters Plan Angle
Both Sides Must
Be Equal
Plan Angle = 45⁰
Plan Angle = 90⁰

24. Edge Bevel Minor Crown End Rafters Plan Angle
Both Sides Must
Be Equal
Plan Angle = 45⁰
Plan Angle = 90⁰
When Can You Use The Plan For the Edge Bevel ?

25. Edge Bevel Minor Crown End Rafters True Angle