Polygon Roof
A polygon roof is a roof with three or more sides with equal slopes and spans
and is commonly used for gazebos or turrets.
Easy Rafters can calculate polygon roofs with up to twelve sides.
To Calculate a Polygon Roof
Select Polygon from the Roof Type dropdown list or click on the appropriate toolbar button
to calculate an polygon roof. The preview window displays a plan view of the polygon roof,
showing the inscribed and circumscribed radii, the width of a face of the polygon,
and the width of a face at the overhang.
Design Tab
Number of Sides
Select the number of sides from the dropdown list.
Slope
Enter or select the slope of the common rafter.
Outer Diameter
Enter the outer diameter of the polygon roof or enter the inner diameter in the next field.
The outer diameter is the diameter of a circle that encloses the points of the polygon
and is equal to two times the span of a hip rafter.
Inner Diameter
Enter the inner diameter of the polygon roof or enter the outer diameter in the previous field.
The inner diameter is the diameter of a circle that fits inside the polygon
and is equal to two times the span of a common rafter.
Overhang
Enter the horizontal overhang of the common rafter including the fascia board.
Heel Height/Seat Cut
Accept the default common rafter heel height and seat cut dimensions or override the defaults
by locking one or the other and entering a new value.
Hip Correction
Select "Drop the Hip" or "Back the Hip" from the dropdown list.
Easy Rafters will calculate the amount of drop or the backing angle required to prevent
the edges of the hip rafter from interfering with the roof sheathing.
Rafter Spacing
Select an on center spacing from the dropdown list.
The spacing is used to layout the jack rafters on the Layout tab
and to calculate the common difference which is also displayed on the Layout tab.
Lumber Sizes
Enter or select the lumber sizes for the common/jack rafters, hip rafters, and fascia boards.
Fascia Type
Select Plumb Cut or Square Cut from the dropdown list.
Drawing Tabs
Hip
The Hip tab displays a dimensioned side view of the polygon roof hip rafter
and a top view of the hip rafter showing the measuring line and angles for the peak and tail cheeck cuts.
Longest Jack
The Longest Jack tab displays a dimensioned side view of the longest jack rafter.
The length of the remaining jacks can ce calculated using the common difference which is
displayed on the Layout tab.
Fascia
The Fascia tab displays a front view of one fascia board
and a top view showing the measuring line and the bevel angles at either end of the fascia board.
Layout
The Layout tab displays a top view of one slice of the polygon roof
showing the layout and lengths of the jack rafters along with the jack rafter common difference.
The jack rafters are calculated to start one half of the spacing distance to either side of center
allowing for easier nailing of the longest jack rafters.
Sheathing
The Sheathing tab displays a plan view of one slice of the polygon roof
viewed at an angle perpendicular to the plane of the roof and
showing the dimensions and angles necessary to calculate and cut the required sheathing.
If the length of a common rafter is longer that the width of a single piece of sheathing
it also displays dimensions for a section equal to the width of a
standard piece of sheathing (48" imperial, 1220 mm metric).
Assembly
Easy Rafters calculates polygon hip rafters with beveled cheek cuts designed to all
meet in the center of the roof. If the roof has more than five or six sides it can be very
difficult to cut the steep angled cheek cuts required.
You may need to modify the hip rafters to suit other joining methods such as using a center block.