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.
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