1. Flat Roofs & Introduction to Gable Roofs Ref: M. S. Martin / March 2004 / Reviewed & Combined March 2007

2. Review Ceiling Frame Calc’s

3. Spec for example following copy on blank paper Joists 150 x 38 sawn Oregon @ 600mm centres, max. span 3.6m Trimmers 100 x 38 sawn Oregon @ 600mm centres Hanging beam 240 x 45 hardwood, max. span of 5.4m On sketch following, draw in joists and hanging beam to scale and indicate trimmer positions also.

4. Sketch picture below allow 100mm for wall frames (not shown) Internal room sizes shown 4.100 3.300 8.350 5.800

5. Formula's No. of joists =width of room- 1 spacing Length of hanging beam = length of room + 2 x wall thickness Trimmers = length of wall – 1 spacing

6. Joists 8.350 – 1.600 = 13.916 – 1 = say 14 – 1 = 13 Order 13 @ 6.0m

7. Hanging beam 4.150 +.200 = 4.350 Order 1 @ 4.5m

8. Trimmers 5.800 – 1= 9.666 – 1.600 Say 10 – 1 = 9 Trimmers at two ends plus internal wall 9 x 3 = 27,27 x.600 = 16.2 lin/m Order 2 @ 6.0m, 1 @ 4.2m

9. Flat roof construction Section 8 – from P306 Flat roofs combine the roof and ceiling frame in one Generally described as one with a pitch less than 10 deg. To allow for extra loads the rafters / ceiling jiosts are increased in sectional size

10. Ceiling types Ceilings can be either lined on the rake or rafters laid flat and use graded battens to give fall to roof

11. Variations to ceilings

14. Skillion roofs - P308 Single sloping roofs Walls at either end of roof at different heights Internal walls parralell to end walls will be at different heights Walls at 90 deg. to end walls will taper in height under the sloping rafters / joists

15. Two ceiling designs

16. Simplest method of marking With skillion roofs the simplest thing is to scribe the rafter over the supporting plates

17. Lean – to – Roof construction P309 This type is constructed against an existing wall or other roof Simple extensions Carports Verandahs Awnings

18. Rafter / Ceiling variations Common on carports, open exposed rafters

19. Other types

20. Calculation of skillion rafters (eg) calculate the quantity of 125 x 50 rafters required for the roof 4.2m long and 2.7m wide, rafter spacings 600mm centres, the difference in height of plates is 900mm Length of rafter = √ (run of rafter)² + (rise)² No. of rafters = (length of building) + 1 spacings

21. Answer – length of rafter √ 2.7² +.900² = √ 7.29 +.81 = √ 8.1 = 2.846 lin/m Order 3.0m lengths 2.700 4.200 900

22. Number of rafters (4.200) + 1.600 = 7 + 1 = 8 Order 8 @ 3.0m rafters

23. Gable Roofs and Components

24. Name the components (handout)

25. Answers Roof Tiles Tile Battens Top Plate Fascia Cornice Ceiling Joist Ceiling Lining Strutting Beam Internal Wall BlockTop Plate Soffit Bearer Stud Soffit Lining Anti-ponding Board Collar Tie Rafter Ridge Purlin Strut Hanging Beam Purlin Strut

26. Gable roof definitions Roof span: Is the horizontal distance measured overall the wall plates Span Plate Stud Section A-A

27. Rise: Is the vertical height measured from the x – y line to where the upper edge of the rafters would intersect Rise

29. Continue on roofs Ridge Rafter Purlin Hanging beam Ceiling joist Strut

30. Set Out for Common Rafter Plumb cut is at the top of the triangle We reduce the centre line length of rafter by ½ the thickness of the ridge to get our true length

31. Birdsmouth has a maximum cut out of one third the rafter depth Level bevel is shown here at base of triangle Back of birdsmouth, is outside of frame and if you take a vertical line up, this is where it meets the x – y line X-Y LINE

32. Set Out on Steel Square Calculate rise per m. run Transfer to steel square Reduced rise Reduced run

33. Set out pattern rafter By either stepping out with square, or by calculation