Gambrel Roof

A gambrel or barn style roof is simply a gable roof with a change in slope partway up the roof. Besides its unique appearance a gambrel roof also serves to maximize the usable floor space in the attic area.

To Calculate a Gambrel Roof

Select Gambrel Roof from the Roof Type dropdown list or click on the appropriate toolbar button to calculate a gambrel roof. The preview drawing displays a dimensioned elevation view of the gambrel roof.

Design Tab

Gambrel Type

Select "Regular" or "Custom" from the Gambrel Type dropdown list.

Regular Gambrels

A regular gambrel fits inside a circumscribed semi-circle and is essentially one half of a regular octagon. Purlins joints are used, slopes are fixed, and the length of the top and bottom rafters (including overhang) will always be equal. The lower height field is disabled, but updates as the buyilding width and/or heel height are changed.

Custom Gambrels

Custom gambrels allow complete flexibility of design with all input fields enabled and few constraints on the shape of the roof other than the lower slope must be greater than or equal to the upper slope.

Joint Type

Select "Purlins" or "Raised" from the Joint Type dropdown list.


The purlin method calculates cuts that bisect the angles at the roof joints. Purlins form the joints between the top and bottom rafters and the ridge board joins the top rafters at the peak. It is also possible to specify "No Ridge/Purlin" for the purlins and/or the ridge board. Plywood gussets could then be used to reinforce the joint if necessary.

Raised (Custom Gambrel only)

The raised joint supports the upper rafters on walls with the lower rafters butted against wall studs. The upper rafters have a heel that raises the upper roof forming a fascia at the joint between the lower and upper roofs with the height of the heel dependent on the size of the upper fascia.

Upper Slope

Enter or select the slope of the upper rafter.
Note: The upper slope is locked for regular gambrels.

Lower Slope

Enter the slope of the lower gambrel rafter or select from the dropdown list.
Note: The lower slope is locked for regular gambrels.

Building Width

Enter the width of the building.

Lower Height

The lower height is the distance from the floor to the peak of the lower rafter.
Note: The lower height is calculated automatically for regular gambrels.


Enter the horizontal overhang of the lower gambrel rafter including the thickness of the fascia board.

Heel Height/Seat Cut

Accept the default heel height and seat cut dimensions calculated by Easy Rafters or override the defaults by locking one or the other and entering the desired measurement.

Note: The default heel for gambrels is 1/2 of the lower rafter plumb cut height.

Lumber Sizes

Enter the lumber sizes for rafters, ridge, purlins, and fascia. If no ridge board is used enter zero for the ridge thickness or select "No Ridge/Purlin" from the dropdown list.

Upper Fascia

The Upper Fascia field appears on the toolbar for Custom Gambrels when the Raised option is selected. Enter the size of the upper fascia board or select a lumber size from the dropdown list. Entering 0 x 0 in the fields will eliminate the upper fascia entirely, but this will leave the upper rafters with very little support. Modifications will will be required.

Note: The upper fascia will always be square cut regardless of the lower fascia type.

Fascia Type

Select Plumb, Square, or Level from the Fascia Type dropdown list. This setting only applies to the lower rafter fascia. The upper fascia for a custom raised gambrel will always be square cut.

Drawing Tabs

Bottom Rafter

The Bottom Rafter tab displays a dimensioned side view of the Gambrel Roof bottom rafter.

Top Rafter

The Top Rafter tab displays a dimensioned side view of the Gambrel Roof top rafter.

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