Week #16 – Roof Modeling and Documentation
16-7. Connecting Roofs in ArchiCAD 15 and Later

ArchiCAD Training (Best Practices Lesson 16-7)

This 21 minute ArchiCAD training lesson explores the methods that may be used in ArchiCAD 15 and later versions to connect roofs to each other, focusing on adding a gable extension to a simple hip roof system.

In ArchiCAD 15 and later, connecting roofs has become much easier in many cases. In addition to the use of the multi-plane roof option, which simplifies creation and editing of roofs with a single plate height, the Connect command generally makes fast work of trimming walls and cleaning up roof elements to each other. However, there are some limitations in the multi-plane roof tool, so there are times when one may need to split up these roofs into single-plane roofs in order to get the highest quality and most flexible result.

After a basic rectangular building is drawn with a hip roof, a gable extension is created. To make this gable extension face the proper direction (ridge line going from the top of the screen to the bottom, rather than side to side), the new roof system is drawn temporarily elongated, then the pivot line polygon is adjusted using the pet palette. To connect this new roof system to the main roof, instead of using the Command-click or CTRL-click method, both roofs are selected and then right-clicked to activate the Connect > Trim Elements to Roof or Shell command. The same command is used to trim the walls to the roofs, instead of using the older Solid Element Operations command.

The gable extension is duplicated twice, each time with a different pivot line height. The roofs are easily cleaned up to each other using the Connect command.

When the gable extension has the same plate height as the main roof, the new roof components can actually be created by modifying the main roof pivot line to follow the bump out of the walls, using familiar pet palette editing commands for the pivot line polygon. The hip extension can be changed to a gable by using the Custom Plane Settings option for that edge of the pivot line.

This flexibility in terms of editing the pivot line polygon also makes easy work of moving the gable extension to line up with the hip end of the main roof.

There are some parts of the connection between roofs that can get tricky, as the choice of using pivot lines or contour lines for the Trimming Body can cause significantly different results, perhaps improving some parts of the model or plan drawing in some cases while compromising other parts of the design. Sometimes it may be necessary or desirable to break up a multi-plane roof into single plane roofs, and edit the roof contours manually or with the help of the traditional Command-click or CTRL-click methods.

Since the Command-click / CTRL-click method does not work with multi-plane roofs, a workaround is demonstrated that involves temporarily splitting up a multi-plane roof to create certain changes in the model, then undoing the split while retaining the changed parts on the clipboard for pasting into place moments later.

Please post your comments and questions below.


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ArchiCAD Training: Connecting Roofs in ArchiCAD 15 and Later

Let us know how you feel... (6 comments so far)

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  1. james Lingard
    11 years ago

    Hi Eric,

    I’m a student learning ArchiCAD. I have been having a problem with roofs, can you tell me if you deal with the following in any of your tutorials.

    I have a model of an existing building – from this I have created all the relevant plans, elevations etc.

    I would now like to make my proposal – this involves a new section of roof intersecting with the existing. The problem is that when I intersect the new roof it looks fine the in proposed model, but when I switch to my existing views it show the sectoin of roof missing where the intersection is taking place.

    I know its possible to control SEO relationships through use of the layer intersection priorities, but this doesn’t seem to work with roofs.

    Am I missing something here?



    • Eric Bobrow
      11 years ago

      James –

      Unfortunately, neither the Renovation filters nor Layer Intersection Priorities affect SEO or Connect operations. This means that if a particular element (such as your existing roof) is trimmed using SEO in either condition (existing or new) then it will show the trim in all views/conditions.

      The best workaround that I know of is to duplicate the element (for example, your existing roof) and designate the original one as Demo (so it will disappear when the renovation filter is set to New) and tag the copy as New (so it will only appear for the New filter). Then your SEO or Connect operations can focus on one condition (either the existing element that will be replaced, or the new one that shows the new condition) rather than affecting both views or conditions.

      This is not elegant, and it does not help in terms of Demolition Plans, but it does work to create clean models for both existing and new conditions.


      • james Lingard
        11 years ago

        Hi Eric,

        Thanks for getting back. Much appreciated that you would take the time to answer. I will go with the work around as you suggest, as you say not quite as neat as it might be but by far the best answer I have found.

        Many Thanks

  2. Albert Aeberhard
    12 years ago

    Hi Eric,
    I have found the setting I have missed. It is the trimming body I had set to contours
    It was best described in the next segment of the lesson.

  3. AlbertAeberhard
    12 years ago

    Hi Eric,
    As usual, your lesson has saved me a lot of time. (I used to split the roof as Christopher did)
    How ever, when a merge the roof after having raised the plate, the main roof is trimed to the edge of the eaves, not to the brickwork. Is it a setting I have missed?

  4. ChristopherEllis
    12 years ago


    Very good ! I have been struggling with this for a while. I usually split roofs to get them to connect. Now, I’ll do it the “right” way !

    I’d be interested to see how the shell tool or morph tools might be used for more fanciful roofs with curving profiles and perhaps as trim boards at the rakes.

    Chris Ellis, Cape Cod, USA