Octagon Framing With the iPhone

How to use RafterTools+ for iPhone to frame an Equal Sided Octagon Roof

Enter an eave angle of 135 and enter the same roof pitch for the Main & Adjacent Rafter Slope Angles. The default is Imperial English, like 8:12 or enter the roof slope angle in degrees and select degrees from the drop down menu box at the top of the screen. Enter the width of the Octagon hip rafter, like 3.5" or enter it in millimeters.  
Then press the calculate button. Press the mm button if you entered the width of Octagon Hip Rafter in millimeters.


Rafter Tools will display the following results for the Octagon roof framing.


Hip Rafter Layout @ Foot of Hip Rafter

Hip Rafter Slope Angle
31.62973°
Main HR Backing Angle
12.25568°
Adjacent HR Backing Angle
12.25568°
Hip Rafter Width
3 1/2''in
Hip Rafter Backing Depth Dimension
3/8''in
Hip Rafter Plumb Line Shift Dimension
3/4''in
Main HR Shift Dimension Perpendicular to HR Run Line
1 3/4''in
Adjacent HR Shift Dimension Perpendicular to HR Run Line
1 3/4''in
Main HR Saw Blade Bevel Angle @ foot of HR 22.50000° 
Adjacent HR Saw Blade Bevel Angle @ foot of HR 22.50000° 



Hip Rafter Layout @ Peak of Hip Rafter

Main HR Back Bevel Angle 19.42694° 
Adjacent HR Back Bevel Angle 19.42694° 
Main HR Saw Blade Bevel Angle @ peak of HR 67.50000° 
Adjacent HR Saw Blade Bevel Angle @ peak of HR 67.50000° 
Main HR Plumb Line Shift Dimension
4 1/4''in
Adjacent HR Plumb Line Shift Dimension
4 1/4''in


Hip Rafter Square Tail Fascia Layout
Hexenschnitt The Witches Cut

Main HR Miter Angle
85.81571°
Adjacent HR Miter Angle
85.81571°
90° - Main HR Miter Angle
4.18429°
90° - Adjacent HR Miter Angle
4.18429°
Main HR Back Bevel Angle
71.38688°
Adjacent HR Back Bevel Angle
71.38688°
Main HR Saw Blade Bevel Angle
18.56691°
Adjacent HR Saw Blade Bevel Angle
18.56691°
Main HR Miter Line Shift Dimension @ tail of HR 9/16''in 
Adjacent HR Miter Line Shift Dimension @ tail of HR 9/16''in



Sent from my iPhone

Press the Lengths Button to calculate the Octagon Hip Rafter Length.

Here I entered a common rafter run of 120" and set the Ridge Width to 0.


Main Rafter Run
120  ''in
Main Rafter TL
144 1/4''in
Main Rafter Length to Ridge
144 1/4''in
Main Rafter OverHang Run
24  ''in
Main Rafter OverHang Rafter Length
28 7/8''in
Main Rafter Seatcut Length
3 1/2''in
Main Rafter HAP
9 1/16''in
Main Rafter Plumb Height
11 7/16''in
Plate Height Difference
0
Hip Rafter Offset From Corner
0
Adjacent Rafter Run
120  ''in
Adjacent King Rafter TL
144 1/4''in
Adjacent King Rafter Length to Ridge
144 1/4''in
Adjacent Rafter OverHang Run
24  ''in
Adjacent Rafter OverHang Rafter Length
28 7/8''in
Adjacent Rafter Seatcut Length
3 1/2''in
Adjacent Rafter HAP
9 1/16''in
Adjacent Rafter Plumb Height
11 7/16''in
Hip Rafter Run
129 7/8''in
Hip Rafter TL
152 9/16''in
Hip Rafter Length to Ridge
152 9/16''in
Hip Rafter Length to Long Point
153 3/8''in
Hip Rafter OverHang Run
26  ''in
Hip Rafter OverHang Rafter Length
30 1/2''in
Ridge Height
89 1/16''in

 Sent from my iPhone

Press the Jacks Button to calculate the Octagon Jack Rafter Lengths.

Here I entered a jack rafter spacing of 12" and set the Jack Rafter Material Thickness to 1.5".

Main Jack Rafter Miter Angle
33.69007°
Main Jack Rafter Bevel Angle
19.01633°
Main Jack Rafter Saw Blade Bevel Angle
67.50000°
Main Jack Rafter Shiften
3 5/8''in
Adjacent Jack Rafter Miter Angle
33.69007°
Adjacent Jack Rafter Bevel Angle
19.01633°
Adjacent Jack Rafter Saw Blade Bevel Angle 67.50000° Adjacent Jack Rafter Shiften
3 5/8''in
Main Jack Rafter Length Difference
34 13/16''in
#1 O.C.=12.00
31 1/2''in
#2 O.C.=24.00
66 5/16''in
#3 O.C.=36.00
101 1/8''in
#4 O.C.=48.00
135 15/16''in
#5 O.C.=60.00
170 3/4''in
#6 O.C.=72.00
205 9/16''in
#7 O.C.=84.00
240 7/16''in
#8 O.C.=96.00
275 1/4''in
Main Special Jack Rafter PL Run
60  ''in
Main Special Jack Rafter Length
168 5/8''in
Adjacent Jack Rafter Length Difference
34 13/16''in
#1 O.C.=12.00
31 1/2''in
#2 O.C.=24.00
66 5/16''in
#3 O.C.=36.00
101 1/8''in
#4 O.C.=48.00
135 15/16''in
#5 O.C.=60.00
170 3/4''in
#6 O.C.=72.00
205 9/16''in
#7 O.C.=84.00
240 7/16''in
#8 O.C.=96.00
275 1/4''in
Adjacent Special Jack Rafter PL Run
60  ''in
Adjacent Special Jack Rafter Length
168 5/8''in
Main Side HR Layout First Jack Rafter
34 3/16''in
Main Hip Rafter Layout JR Difference
36 13/16''in
Adjacent Side HR Layout First Jack Rafter
34 3/16''in
Adjacent Hip Rafter Layout JR Difference
36 13/16''in


Sent from my iPhone

For Advanced Timber Framing Angles for the Octagon roof press the Timber Framing Angles Button.


 For Advanced Hip Rafter Framing Angles for the Octagon roof press the Hip Angles Button.

You can select any of the lines in the Hip Angles display to show the Framing Square usage for the selected angle.



The easiest way to frame an Octagon roof iis with the 4-Butt method.


The Octagon Roof Framing 4 Butt Hip Rafter Method.
  • #1 Main 2 Butt Hip Rafter Length
    Cut 2 hip rafters at the TL length. These hip rafters will be installed first. The hip rafter head cut will have the Octagon Hip Rafter Slope Angle for the plumb cut angle and will not be beveled.
  • #2 Side 2 Butt Hip Rafter Length
    Cut 2 hip rafters minus 1/2 the thickness of the Octagon Hip Rafters. These hip rafters will be installed second, against the first two hip rafters. The hip rafter head cut will have the Octagon Hip Rafter Slope Angle for the plumb cut angle and will not be beveled.
  • #3 Mitered Hip Rafter Length
    Cut 4 hip rafters that are mitered, see below for length. Set the saw Blade Bevel Angle at 45.00°. The hip rafter head cut will have the Octagon Hip Rafter Slope Angle for the plumb cut angle and be beveled.
  • #4 Mitered King Common Rafter Length
    Cut 8 king common rafters, see below for length. These king common rafters will be beveled. Set the saw Blade Bevel Angle at 67.5°. The king common rafter head cut will have the Octagon Rafter Slope Angle for the plumb cut angle.




For the mitered Octagon Hip Rafter use


Hip Rafter Slope Angle = 31.62973°
Half Thickness of Octagon Hip Rafter = 1.75"
Hip Rafter TL = 152 9/16''in = 159.5625"

1.75 ÷ cos(45°) = 2.47487
2.47487 ÷ cos(31.62973°) = 2.90664"
Mitered Octagon Hip Rafter Length = 159.5625 - 2.90664" = 156.65585"


For the mitered King Common Rafter use

Common Rafter Slope Angle = 33.69007°
Common Rafter Length =144 1/4''in
Half Thickness of Octagon Hip Rafter = 1.75"

1.75" ÷ sin(22.5°) = 4.5730
4.5730" ÷ cos( Roof Slope Angle)
4.5730" ÷ cos(33.69007°) = 5.4960"

144.25 - 5.4960 = 138.7539" 
Mitered King Common Rafter Length = 138.7539"


RafterTools for Android has the Octagon 4 butt method lengths built into the calculator app.




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