SBE Builders

Strong Built Establishments Builders

SBE Builders is a commercial and residential framing contractor located in Discovery Bay California. Dedicated to the art of Carpentery & Roof Framing. We are the professionals for the future of the craft of carpentry.

This Barrel Roof Dormer calculator will return roof framing trigonometry & geometry details for:

  1. Barrel Roof Semi Major Axis of the Elliptical Valley Footprint
  2. Barrel Roof Plan View Run of the Ellipse from the intersection of the barrel roof and main roof.
  3. Total Arc Length of Barrel Roof
  4. Arc Angle of Purlin Rafter Spacing
  5. Cord Length of Purlin Rafter Spacing
  6. Ellipse layout points on Main Roof Surface
  7. Purlin Rafters cut perpendicular to Roof Surface
  8. Purlin Rafter Slope Angle
  9. Purlin Rafter Miter Angle
  10. Purlin Rafter Saw Blade Bevel Angle
  11. Barrel Roof Plan View Rafter Lengths
  12. X & Y Points for Elliptical Ploting of the Ellipse on the Main Roof Surface
  13. Real Roof Surface plotting points for the plywood roof sheathing
  14. Ellipse Valley Sleeper Offset
  15. Purlin Rafter Deduction for Ellipse Valley Sleeper Offset

Barrel Roof Dormer Framing Calculator

Barrel Roof Details
    Main Roof Pitch

Purlin Rafter O.C. Spacing
Entered in Inches

    Barrel Roof Radius
Entered in Inches

show results in feet & inches

results are show below in the IFrame window

Pitch Break Shed Roof Dim

Barrel Roof Framing

Barrel Roof Framing Math & Trigonometry

Main Roof Semi Major Axis = radius  sin(Roof Pitch Angle)
Plan View Run Semi Major Axis = radius  tan(Roof Pitch Angle)
Arc Angle Of Spacing in Radians = spacing  radius (This gives you the arc angle in radians)
Degree to Radians = 3.141593  180   = 0.017453
Radians to Degrees = 180  3.141593  = 57.29578
Arc Angle of Spacing in Degrees = (spacing  radius ) * 57.29578 = Arc Angle in Degrees

i = 1,2,3...etc
point_x = radius * cos(90 - (Arc Angle Of Spacing Radins * i))
point_y_on_ellipse = Semi_Major_Axis * sqrt((Semi_Minor_Axis * Semi_Minor_Axis) - (point_x * point_x))  Semi_Minor_Axis
Plan View Purlin Rafter Length =  point_y_on_ellipse * cos(Roof Pitch Angle)
Purlin Slope Angle  = arcsin(point_x  radius)

Purlin Face Cut Perpendicular to Roof Surface
Saw Blade Miter  Angle = arctan (cos(Purlin Slope Angle)  tan(Roof Pitch Angle))
Saw Blade Bevel Angle = arcsin (cos(Roof Pitch Angle) * sin(Purlin Slope Angle))

Download Barrel Roof Dormer Framing Drawing in DXF format
Barrel Roof Dormer Framing.dxf -- auto generated DXF CAD file of Barrel Roof Dormer Framing drawing each time script is run
barrel roof DXF File

Barrel Roof Eliptical Valley Offset

You can bevel the ellipse valley sleeper material or slide the ellipse valley sleeper material down hill by the ellipse valley sleeper offset dimension.
When you offset the ellipse valley sleeper, the ellipse dimensions stay the same for both ellipses.
In the image below you can see the direction of the ellipse valley sleeper bevel is a constant dimension between the two ellipses.


Real Roof Surface Layout on Plywood Roof Sheathing for Barrel Roof Dormer Sheathing

Barrel Roof Sheathing


Down load the Barrel Roof Cut Out Pattern HERE for a paper model of the barrel roof geometry.


Barrel Roof Cut Out Pattern


RFI | structural | framing | online tools | company | site map
safety | building resource links | build it green | photo gallery | Octagon | crown molding angles | home
WindsorOne Protected Trim

SBE Builders
SBE Builders
5305 Laguna Ct.
Discovery Bay, California 94505
(925) 634-6022 • Fax: (925) 634-6022
Commercial & Residential Framing Contractor
American Carpenter and Builder
California Licensed General Building Contractor
CA LIC.#  546126

Roof Framing Geometry

  • Roof framing geometry is empirical-type knowledge.
  • Information gained by means of observation, experience, or experiment.
  • From ground Line 0: Z1, Z2, Z3 etc...
  • To Roof Axis 0: A1, A2, A3 etc...
  • To the bring back line 0 for scribing: B1, B2, B3 etc...

Roof Framing Geometry Blog

Rafter Tools for Android
With Quad Tetrahedra Analytic Algorithm Technology.
Helping apprentice carpenters on their journey to becoming master carpenters with Certification in roof framing.

Rafter Tools+ for iPhone

Rafter Tools+ is a rafter calculator for complex roof framing angles that other roof framing calculators don't offer.


Stair Tangent for iPhone

This iPhone app is for rough frame carpenters that don't build stairs everyday, but could use an stair app calculator to check their stair building calculations. Build a set of stairs that you are gonna be proud of. With Stair Tangent you can elimenate cumulative math errors when building - constructing stairs.

Stair Tangent

Crown Molding Tools

Crown Molding Tools  

Carpenters Of Steel

Canadian & American Geometric Roof Framing Development
using a Steel Framing Square

Geometric Roof Framing Development for Irregular Hip Roof Calculations
using a Steel Framing Square

Geometric Development of Tetrahedron
using a Steel Framing Square

Hip Rafter Backing Bevel Angles from 1565 to 2013

Applied Geometry and Euclidean GeometryA lesson in Applied Geometry and Euclidean Geometry

This Is Carpentry

We're a member of the Timber Framers Guild

Timber Framers Guild

American College of the Building Arts, carpentry and timber framing programs.

American College of the Building Arts

Website Usage Legal Policy