Irregular Hip Roof Rafters


Input variables

  1. Roof Eave Angle
  2. Main Pitch Angle
  3. Adjacent Pitch Angle
  4. Input Length
  5. Overhang Run
  6. Jack Rafter Spacing
  7. Hip Rafter Width
  8. Hip Rafter Depth
  9. Jack Rafter Width -- Common Rafter Width
  10. Main Rafter Depth
  11. Seat Cut Level Cut Length
  12. Ridge Width
For Input Length use any part of the hip roof rafter geometry as input to find the rest of the angles.
Calculated Results for the Irregular Hip Roof Rafter function. 

  1. Main Plan Angle
  2. Main Roof Pitch Angle
  3. Main Roof Pitch
  4. Adjacent Plan Angle
  5. Adjacent Roof Pitch Angle
  6. Adjacent Roof Pitch
  7. Main Rafter Run
  8. Main Theoretical Rafter Length
  9. Main Rafter Length To Ridge
  10. Main Rafter Seatcut Length
  11. Main Overhang Rafter Length
  12. Adjacent Rafter Run
  13. Adjacent Theoretical Rafter Length
  14. Adjacent Rafter Length To Ridge
  15. Adjacent Rafter Seatcut Length
  16. Adjacent Overhang Rafter Length
  17. Hip Rafter Angle
  18. Hip Rafter Pitch
  19. Hip Rafter Run
  20. Hip Rafter Theoretical Rafter Length
  21. Hip Rafter Length plumb to plumb along the center line to the ridge.
  22. Hip Rafter Long Point Length to Ridge -- long point of hip rafter sidecut
  23. Saw Blade Bevel Angle to cut the hip rafter sidecut angle along the hip rafter peak plumb line.
  24. Hip Rafter Overhang Length
  25. Main Pitch First Jack Rafter Length To Long point of miter cut.
  26. Main Pitch Jack Rafter Length Difference @ jack rafter spacing
  27. Main Pitch Jack Rafter Saw Blade Bevel Angle
  28. Adjacent Pitch First Jack Rafter Length To Long point of miter cut.
  29. Adjacent Pitch Jack Rafter Length Difference @ jack rafter spacing
  30. Adjacent Pitch Jack Rafter Saw Blade Bevel Angle
  31. Theoretical Common Rafter Rise
  32. Rise To Top Of Ridge
  33. HAP -- Height Above Plate (Heel Height)
  34. Main Rafter Plumb Cut Height
  35. Adjacent Rafter Plumb Cut Height
  36. Hip Rafter Plumb Cut Height
  37. Hip Rafter Drop For Roof Plane Alignment
  38. Hip Rafter Backing Depth Mark.
  39. Hip Rafter SideCut Mark For Side Cut Angles.
  40. Main Hip Rafter Offset Mark Perpendicular To Hip Run Line.
  41. Adjacent Hip Rafter Offset Mark Perpendicular To Hip Run Line.
  42. Hip Rafter Backing Offset Main along eave line.
  43. Hip Rafter Backing Offset Adjacent along eave line.
  44. Hip Rafter Backing Angles
  45. Hip Rafter Plumb Backing Angle
  46. Hip Rafter Side Cut Angles
  47. Jack Rafter Side Cut Angles
  48. Roof Sheathing Angles
  49. Hip Rafter Purlin Housing Angles
  50. Hip Rafter Diamond Post Miter & Saw Blade Bevel Angles
  51. Plywood Roof Sheathing Offset Cut Line
  52. Valley Sleeper Miter & Saw Blade Bevel Angles
  53. Dormer Square Tail Miter & Saw Blade Bevel Angles
  54. Purlin Rafter Miter & Saw Blade Bevel Angles
  55. Purlin Layover cut perpendicular to roof surface plane

Roof Eave Angle
This is the corner angle of the building. Most Roof Eave Angle corners are at 90°. For irregular or bastard hip roofs the Roof Eave Angle can be between 35° and 150° You'll get an Unconstructable error message if the roof is unconstructable with the current input parameters.

Main Roof Pitch
Select the input type from the input menu, Imperial/English Inch base 12 —— default, enter roof pitches from 1—24 like 8 for an 8:12 pitched roof, Metric 300mm base, enter millimeters like 200 for a 33.69007° roof pitch angle, Decimal Inch base 10 —— enter base 10 decimal numbers like 5.7735 for a 30° roof pitch angle, Degrees input —— use any roof angle in degrees like 33.69007°

Adjacent Roof Pitch
Select the input type from the input menu, Imperial/English Inch base 12 —— default, enter roof pitches from 1—24 like 8 for an 8:12 pitched roof, Metric 300mm base, enter millimeters like 200 for a 33.69007° roof pitch angle, Decimal Inch base 10 —— enter base 10 decimal numbers like 5.7735 for a 30° roof pitch angle, Degrees input —— use any roof angle in degrees like 33.69007°

The input mode selection can be completely different from the output mode

    Input Menu Mode
  1. Imperial/English Inch base 12 —— default.. use American standard pitches over 12.
  2. Metric 300mm base —— 300mm is 11.81102 inches, similar usage to the American framing squares printed in inches.
  3. Decimal Inch base 10 —— use this option when working with tangents or using the Chappell Master Framing Square multiply the tangent of the angle by 10
  4. Degrees

The output mode selection can be completely different from the input mode

    Output Menu Mode
  1. Imperial/English Inch base 12 —— default.. use American standard pitches over 12.
  2. Metric 300mm base —— 300mm is 11.81102 inches, similar usage to the American framing squares.
  3. Decimal Inch base 10 —— use this option when working with tangents or using the Chappell Master Framing Square

Input Length Type
This menu option allows you to select different parts of the hip roof for calculating the angles and dimensions of the irregular hip roof.

Overhang Run
This menu option allows you to set the major pitch rafter overhang run. The minor pitch rafter overhang run will be calculated from the rise of the major pitch rafter overhang run. The major and minor overhang runs will only be the same when the the major and minor pitches are the same.

Jack Rafter Spacing
This menu option allows you to set the jack rafter On Center spacing of the jack rafters. The length of the first jack rafter will be calculated from the building corner with the jack rafter spacing. If you enter a jack rafter spacing of 24" and 1.5" for the jack rafter width, then the length of the first jack rafter will be calculated from a wall run of (24" + 1/2 of the jack rafter width) 24.75" from the corner of the building.

Hip Rafter Width
This menu option allows you to set the width of the hip rafter. The width of the hip rafter is used to calculate:

Hip Rafter Material Depth , Main Material Depth
This menu option allows you to set the depth of the rafters that is used to calculate:

Seat Cut Level Cut Length
This menu option allows you to set the length of the seatcut of the major pitch rafters that is used to calculate:

Ridge Width
This menu option allows you to set the width of the common rafter ridge. It is used to calculate:

Hip Rafter Layout


Plan Angles
The plan angles are calculated from the Eave Angle and the Main and Adjacent Roof Slope Angles. The plan angles will align the two roof planes on the center line of the Hip Rafter.

Hip Rafter Offset/Shift
The Hip Rafter Offset/Shift aligns the edges of the hip rafter material with the roof planes which are determind by the given Roof Slope Angles. This dimension is perpendicular to the hip rafter run line. You will layout the top of the unbacked hip rafter with these dimensions.

Hip Rafter Plumb Line Shift
The hip rafter plumb line intersects the corner of the building. Draw a line parallel to the hip rafter plumb line shifted the dimension using the Hip Rafter Plumb Line Shift Dimension at Foot Of Hip Rafter. The shifted plumb line will align the edges of the hip rafter for roof plane alignment with the HAP of the common rafters at the plate line. Use this same dimension for drawing the hip rafter tail miter angle for plumb cut rafter tails.


Hip Rafter Plumb Line Shift at Peak of HR
Draw a line parallel to the hip rafter plumb line at the peak of the HR shifted the dimension using the Hip Rafter Plumb Line Shift Dimension at Peak Of Hip Rafter. The shifted plumb line will align the edges of the hip rafter for roof plane alignment with the top edges of the common rafters at the ridge. Use the given saw blade bevel angles along these shifted plumb lines to cut the hip rafter side cut angles. Cutting the hip rafter plumb line with the given saw blade bevel angle will form the hip rafter side cut bevel angles at the peak of the hip rafter.

Hip Rafter Backing Depth
Draw a line on the side of the hip rafter using this dimension.

The Hip Rafter Plumb Lines are cut before you back out the hip rafter
After the hip rafter is completely laid out and the plumb lines are cut use the hip rafter backing angles to edge bevel the hip rafters for the correct hip rafter backing angle.

Hip Rafter Offset Example

Use this link to view drawing examples of hip rafter offset/shift for irregular hip roofs
Hip Rafter Offset/Shift Examples

Use this link to view irregular hip rafter layout
How to Precisely Layout an Irregular Pitch Hip Rafter


View the Irregular Hip Roof Valley Rafter Framing Blog
for how to layout the hip rafter backing depth mark and the hip rafter side cut mark for Hip Rafter side cut angles.
View the Hip Rafter Roof Plane Alignment Blog
for more examples of the Hip Rafter Plumb Mark Line Shift on equal pitched roofs.
View the Hip Rafter Plumb Mark Line Shift Blog
for more examples of the Hip Rafter Plumb Mark Line Shift on unequal pitched roofs.
View the Hip Rafter Offset Blog
for more examples of the Hip Rafter Offset Line on unequal pitched roofs.