RAFTERS. Single and Continuous Spans

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2 Single and Continuous Spans Restraint value for slenderness calculations is 1200 mm, in 10, 20, 40( kg/m 2 ) (Restraint may be by Roof Battens) Restraint value for slenderness calculations is 600 mm, in 70, 90 ( kg/m 2 ) (Restraint may be by Tile Battens) K6 factor of 1.0 used. K23 factor applied to bending strength. INCLUDES J2 value of 1.5 used for DL Deflection. 10 kg/m 2 Pre-camber radius of 0m used. 20 kg/m 2 Roof Pitch of 25.0 deg used in load calculations. 40 kg/m 2 N3 WIND AREAS Downdrag loads were ignored. 70 kg/m 2 Total Uplift coefficient was kg/m 2 1: Dead Load = Span / 300 or maximum 20 mm. 2: Roof Live Load = Span / 250 3: Wind Uplift = Span / 150. Timber Properties: Fb = 11 MPa, Elasticity = MPa Density = 600 kg/m3, Fs = 1.25 MPa Ft = 5.2 MPa, Fc = 11 MPa. Timber Properties: Fb = 11 MPa, Elasticity = MPa Density = 600 kg/m3, Fs = 1.25 MPa Ft = 5.2 MPa, Fc = 11 MPa. Load Cases: 1: Dead Load 2: Roof Live Load 3: Wind Uplift MAX ROOF PITCH = 25 DEGREES Roof pitch used in calculations is 25 degrees for Roof pitches greater than 25 degrees but not exceeding 45 degrees you may multiply rafter span (Plan View ) x 1.28 then use answer to read rafter span as normal. CONTINUOUS SPAN RAFTERS Continuous Rafter may have unequal spans, provided major span does not exceed 1.25 times the length of the minor span, major span length should be used in determining rafter size. 8

3 Diagrams for use in determining rafter span ( plan width) for use in rafter tables. Max roof pitch 25 degrees. Single Span Rafter OH OH SPAN SPAN Birdsmouth and overhang details For Rafters Birdsmouthed up to 1/3 of their depth reduce Max Overhang as read from table by 35%. Maximum Overhang Figure 16 Continuous Span Rafter OH SPAN SPAN Major Minor Span 9

4 Roof load of Light Sheet (10kg/m2) Maximum Permissible Span (m) Single Span Continuous Span Beam Rafter Spacing (m) Beam Rafter Spacing (m) Size Size x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x Bearing Lengths: 35mm for single span supports, or end supports for continuous members. 45mm for internal supports on continuous members or cantilever supports. 10

5 Roof load of Sheet (20kg/m2) Maximum Permissible Span (m) Single Span Continuous Span Beam Rafter Spacing (m) Beam Rafter Spacing (m) Size Size x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x Bearing Lengths: 35mm for single span supports, or end supports for continuous members. 45mm for internal supports on continuous members or cantilever supports. 11

6 Roof load of Sheet & Ceiling (40kg/m2) Maximum Permissible Span (m) Single Span Continuous Span Beam Rafter Spacing (m) Beam Rafter Spacing (m) Size Size x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x Bearing Lengths: 35mm for single span supports, or end supports for continuous members. 45mm for internal supports on continuous members or cantilever supports. 12

7 Roof load of Tiles (70kg/m2) Maximum Permissible Span (m) Single Span Continuous Span Beam Rafter Spacing (m) Beam Rafter Spacing (m) Size Size x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x Bearing Lengths: 35mm for single span supports, or end supports for continuous members. 45mm for internal supports on continuous members or cantilever supports. 13

8 Roof load of Tiles & Ceiling (90kg/m2) Maximum Permissible Span (m) Single Span Continuous Span Beam Rafter Spacing (m) Beam Rafter Spacing (m) Size Size x x x x x x x x x x x x x x x x x x * 126 x x x x x x x x x x x x x x * 420 x x * 126 x x x x x x x x x x x x x x x x x x * 504 x x * Bearing Lengths: 35mm for single span supports, or end supports for continuous members. 45mm for internal supports on continuous members or cantilever supports. *For continuous spans: denotes member must have a min 65mm bearing length at the internal support, and 45mm for ends supports of continuous members. 14

9 RAFTER OVERHANGS Maximum Permissible Overhang (m) Plan Dimension Roof load of Light Sheet (10kg/m2) Roof load of Sheet (20kg/m2) Beam Rafter spacing (m) Beam Rafter spacing (m) Size Size x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x Overhangs from this table, suitable for rafters without birdsmouths only. For rafters with birdsmouths, see figure 16 Maximum Overhang Figure 16 Birdsmouth and overhang details For Rafters Birdsmouthed up to 1/3 of their depth reduce Max Overhang as read from table by 35% 15

10 RAFTER OVERHANGS Maximum Permissible Overhang (m) Plan Dimension Roof load of Sheet & Ceiling (40kg/m2) Roof loroof load of Tiles (70kg/m2) Beam Rafter spacing (m) Beam Rafter spacing (m) Size Size x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x x Roof load of Tiles & Ceiling (90kg/m2) Beam Rafter spacing (m) Beam Rafter spacing (m) Size Size x x x x x x x x x x x x x x x x x x Overhangs from this table, suitable for 294 x Overhangs from this table, suitable for rafters without birdsmouths only. For rafter with birdsmouths, see figure