Jack rafters

how does one create a hip roof?
especially the jack rafters

when given a house size?

Personally, I model roof framing with a bunch of 2x4 or 2x8 groups. Angle them to the roof pitch and then cut them appropriately. Then make a collection of groups into components that I can repeat through the roof.

I think that @medeek may have an extension for that, too.

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There are plugins as Aaron indicated, but doing it from scratch–you can imagine that a jack rafter is just a common rafter, laid out to intersect the hip. put it in place and cut with the hip. The hip rafter in a square house is a board rotated to (rise per common foot)/17. In this method each jack has to be done this way (or stretch a pre-cut jack) but you can take the whole set and flip it to go on the other side of the hip or use at other hips.

“Given a house size”, I’d lay out the top plates and just build it board by board (groups and components) from there like in real life, except the computer does a lot for you that you don’t have to figure. You can make the rafters long and use the other boards to cut it (solid tools) or “mark” the cut–and using components you can work with many instances of the same rafter. And you get to use the computer to make the layout 2’ on center etc. Easy to move them all over at once if you want, or try different lay outs.

Hint: Solid Tools takes away component definition so work inside the component to preserve it --or use a plugin. Eneroth has one I hear. I just don’t happen to use it.

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Arguably the rafter framing module of the complex module of the Truss plugin is still a work in progress, but it will generate jack rafters now:

If you are just drawing a simple hip roof then all of the rafters, hips etc… are drawn.

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It’s fairly easy to do manually but it would be nice to be able to do it generatively. Make groups of the joists and the cutting plane. intersect the faces. Copy the resulting faces into each joist and erase the extra faces. I can post an example if you are in need. Here it is with tension rod pulling it all together for framing.skp (665.9 KB)


hi there
I thank all of you for your replies.
I did not really specify what I am doing. I am retired and use SU for play only and was watching ‘this old house’ and they created a hip roof
so I was wondering if I could draw that in SU
what I really am after if what you called 2x8 hp joist the one which carries the rafters which get shorter as you go down
if I use a regular rafter and turn it by its z-axis for 45 degrees I comes out of the rood plane

what are the steps you use to draw that one so to meets the top beam and the bottom plate and still stays within the roof plane?

and I don’t have to buy an extension (I am not going to build it and I don’t nmake money by doing it)



My method would actually be to draw a 2x8 board component and rotate it to the hip angle, place it at the corner then position vertically so the edges are the plane of the tops of the common rafters.

The common rafters pitch is described (in inches) X/12 where “X” is the vertical dimension that comes in 12" horizontal. The hip rafter is X/17, so if you simply rotate a common rafter it is too steep for the hip.

If the common or nominal roof pitch is say 5/12 the hip will be 5/17.

To illustrate you can align the hip by placing common rafters out each side of the corner --starting same distance from the corner, each side. the interections will give the angle of the hip. Or you can use the protractor to create a guide at your hip pitch. A simple shape of the roof also gives an edge with the hip pitch.

The hip birdsmouth is also adjusted (hip rafter moved vertically) so that the line of the hip is in the plane of the two sides.

FYI the roof pitch can be entered using the protractor or the rotate tools by typing "X:12"

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