Page 114 - roofing

PITCHED ROOF CONSTANTS

PITCH RISE RAFTER HIP/VALLEY

15° 0.27 1.03 1.44
17.5° 0.32 1.05 1.45
20° 0.36 1.06 1.46
22.5° 0.41 1.08 1.47
25° 0.47 1.10 1.49
27.5° 0.52 1.13 1.51
30° 0.58 1.16 1.53
35° 0.70 1.22 1.58
37.5° 0.77 1.26 1.61
40° 0.84 1.31 1.64
45° 1.00 1.41 1.73
50° 1.19 1.56 1.85
52.5° 1.30 1.64 1.92
55° 1.43 1.74 2.01
60° 1.73 2.00 2.24
70° 2.75 2.92 3.09

Rafter Rafter

Run Run ???
To calculate the length of Rise, rafter or Hip / Valley multiply the run by the required constant corresponding to the appropriate pitch.Run = 3.08m

EXAMPLE 1) USING TABLE THEREFORE Hip = Scaled at 4.87m

Pitch = 35° Rafter = Run x 1.22
Span = 6.16 = 3.08 x 1.22 = 3.76m
Run = 3.08 Hip = 3.08 x 1.58 = 4.87m

ii) By Scale drawing i.e using the scale, rule to reproduce the legth of Scale
the rafter and in our case the run away from from the corner of the 1:50
paper (90) and scaling the resulting valley or hip measurement. Rafter = 3.76m

114 ROOFING – ISSUE 1