General Info

In this section you will find some general truss tips. Click the arrows on the bottom of each page to navigate.
     
 

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Compute Rafter Length

Match New to Existing Roof

Order Specify

     

Instructions to compute the rafter length of a roof truss

     
RAFTER.JPG
         

Pitch

Cosine

 

Pitch

Cosine

2.0 0.9864   7.5 0.848
2.5 0.979   8.0 0.8321
3.0 0.9701   8.5 0.816
3.5 0.96   9.0 0.8
4.0 0.9487   9.5 0.7841
4.5 0.9363   10.0 0.7682
5.0 0.9231   10.5 0.7526
5.5 0.90906   11.0 0.7372
6.0 0.8944   11.5 0.722
6.5 0.8793   12.0 0.7071
7.0 0.8638    

RAFTER LENGTH = [HORIZONTAL DISTANCE TO PEAK (FEET) + OVERHANG LENGTH (FEET)] DIVIDED BY COSINE OF THE PITCH

TO CONVERT DECIMAL FEET TO INCHES, MULTIPLY BY 12

TO CONVERT DECIMAL INCHES TO SIXTEENTHS OF AN INCH, MULTIPLY BY 16

EXAMPLE RAFTER LENGTH FOR 24' 6/12 COMN WITH 16" OVERHANGS:

DISTANCE TO PEAK = 24' / 2 = 12'

OVERHANG LENGTH = 16" / 12 = 1.3333'

TOTAL HORIZONTAL DISTANCE = 13.3333'

RAFTER LENGTH = 13.333 / 0.8944 = 14.9076'... 0.9076' X 12 = 10.8912"... 0.8912" X 16 = 14/16"

RAFTER LENGTH = 14-10-14 OR 14' 10-7/8"

 

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