Strong Built Establishments Builders SBE Builders is a commercial and residential framing contractor located in Discovery Bay California. Our Systematic Construction Logic produces Strong Built Establishments. E-Defense stands for Earthquake-Defense. Is your building ready for the next Earthquake?

Bowed Bay Window Rafter Calculator with Unequal Overhang v1.0

Span in inches     Number of Bay Windows > 1     Projection Of Bay Windows     or enter Bay Window Angle     Rafter Overhang 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48     Rafter O.C. Spacing At Plate Line 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48  P   Major Rafter Pitch 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24     or enter Major Angle show results in feet & inches results are show below in the IFrame window

Warning this bow window roof framing should only be attempted by master roof cutters and stackers.
Check the printed results with the auto generated DXF file each time this script is run.

At the bottom of this page there are links to diagrams, sketchs and bowed window roof framing development of this script.

All online tools use javascript to calculate the dimensions. Use at your own risk. If the answers look wrong then verify the answers with a calculator or with Joe Bartok.

Bow Window with Unequal Overhang Example

Bowed Baywindow Diagram Joe Bartok's Bowed Baywindow Sketch with 5 bays
Bowed Baywindow Diagram Joe Bartok's Bowed Baywindow Sketch with 7 bays
Bowed Baywindow Projection Solver Joe Bartok's Bowed Baywindow Projection Solving Calculator
Bowed Baywindow Trial Angle Solver Joe Bartok's Bowed Baywindow Trial Angle Solving Calculator

Bowed Baywindow Sketch Bowed Baywindow Sketch with 5 bays
King Common Run in Bowed Baywindow Sketch King common rafter run with medians and altitudes scalene triagnles
Odd Numbers of Bays Dimensioning Bowed baywindow dimension example of how the projection is calculated with odd number of bays
Even Numbers of Bays Dimensioning Bowed baywindow dimension example of how the projection is calculated with even number of bays
Bow Window 2 Sided Bowed baywindow dimension example with 2 baywindows
Bow Window Perl and Javascript comparison test script Bowed baywindow best fit results comparison

Code used to calculate projection offset for Bowed Baywindow For Odd Number Of Bays

central_angle = theta * bays
radius = span /(2 * sin(central_angle / 2))
d = radius * cos(theta / 2)
side_angle = (PIE - central_angle) /2
radius_layout_offset  = (span/2) * tan(side_angle)
offset = d - radius_layout_offset 

central_angle = theta * bays
radius = span /(2 * sin(central_angle / 2))
d = radius * cos(theta / 2)
side_angle = (PIE - central_angle) /2
radius_layout_offset  = (span/2) * tan(side_angle)
offset = radius - radius_layout_offset 

Bow window: A composite of two or more window units in a radial or bow formation also known as a walk-out bay window installation where the wall follows the bowed out angle of each window. Or a rounded Bay Window which projects in a semi-circle from the surface of an exterior wall.

The DXF file generated each time the script in run will have the arc construction lines drawn as well as the plan view of the hip rafters.

King common rafter runs clarification.

Each bay window roof plan triangle, formed by the fascia line and 2 bay hips, is a scalene triangle. Which means all 3 sides of the triangle are unequal in length. Because of the unequal sides of the triangle the normal king common rafter run is often located outside of the bay hips when drawn at a 90° to the plate line.

OPTION # 1:
King hip rafter runs for each bay are located in the center of the bays hip rafters. This is the same as the median of a triangle.\nThe king hip rafter runs are not located in the center of the baywindow wall framing. The king hip rafters are not at 90° degrees to the plate line or fascia line. By locating the king hip rafters in the center of the bays hip rafters, each king hip rafter will be centered in the fascia line of each bay.

OPTION # 2:

Or if you prefer to use the altitude of each bay for common rafter runs. You can use the information printed out at the bottom of the results to calculate the common rafter lengths with the altitudes for the common rafter runs.

SBE Builders 5305 Laguna Ct. Discovery Bay, California 94505 (925) 634-6022 • Fax: (925) 634-6022 Commercial & Residential Framing Contractor Build it Green Framing Contractor American Carpenter and Builder Licensed 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...