Gambrel Roof Slope

Well let s face it it s a very attractive roof design but there are practical considerations as well.

Gambrel roof slope.

The rule of thumb that i use when designing a gambrel is that the top pitch should be no less than half the pitch of the bottom. A gambrel or barn style roof is simply a gable roof with a change in slope partway up the roof. The picture below shows the pitch of a 7 12 roof slope meaning that for 12 of horizontal measurement roof run the vertical measurement roof rise is 7. A gambrel or a barn roof is much like mansard in a sense that it has two different slopes.

When you are designing your shed roof whether it be a gambrel gable or saltbox you should never have any roof pitch less than a 3 12. Check overhang to calculate rafter overhang equal to the lower level cut at the full rafter depth. The shallower the top pitch the more squatty it will look. In other words if you start with a say 14 12 bottom pitch your top pitch should be 7 12 or greater.

Anything less than this will ultimately result in a roof that leaks if you plan on putting shingles on it. A gambrel style is often called a barn roof. A roof similar to a mansard but sloped in one direction rather than both. A gambrel or gambrel roof is a usually symmetrical two sided roof with two slopes on each side.

Similar to mansard the lower side of the gambrel roof has an almost vertical steep slope while the upper slope is much lower. Maximum height in the center height at the pitch break how far in from the side wall a six foot height occurs etc. A roof with the shallow slope below the steeper slope at the eaves. The usual architectural term in eighteenth century england and north america was dutch roof the upper slope is positioned at a shallow angle while the lower slope is steep.

Move slider or directly enter angle to alter sweep angle of lower rafters and change the shape. A gable roof has only two rafter or truss chord angles a top cut at the peak and a bottom cut at the walls. Gambrel roof framing geometry calculator inch this gambrel roof fits in a semicircle and starts as the top half of an equal sided octagon. The difference between the two is that the gambrel only has two sides while the mansard has four.

This means that for every 12 horizontal run you must have at least 3 of rise. Compare with bell roof. Its double or sometimes triple slopes on each side of a peak provide more space inside the roof which is attractive to homeowners too. Besides its unique appearance a gambrel roof also serves to maximize the usable floor space in the attic area.