Gable Roof - "Cannot Join Roof" Plague

[BigPicture045]

I am trying to get the gable on the right to join to the main roof. The gable on the left joined fine. The roof location where it comes down on the existing roof needs to be about where it is.

This cannot join roof error has been plaguing me for years. Why is adding a basic gable so difficult for me? I've attached the Revit File.

[ToanDN]

Nothing attached but I guess you create the main roof using Pick Walls + Overhang so an eave of the gable is outside the actual footprint of the main roof.

[Lance.Coffey]

Thank you for the question @BigPicture045!

Searching online, I found this thread on a similar topic (not sure if that info helps), but without a copy of the Revit model to review it’s hard to say what combination of geometry is leading to the error.

Regarding attaching the file, it may have been too big to attach. One way to reduce the file size would be to use the following steps:

1. Create a local copy of the original model (so these changes won't affect the production file).
2. Select the affected roof elements.
3. Group the selected elements.
4. With the group instance selected use the Link command to convert the group to a link.
5. Check that the same error occurs in the link model.
6. Attach the newly created link.

[BigPicture045]

I didn't realize that the revit file was not attached earlier. I am trying to get this gable to attach to the roof. I have attached a similar roof in the revit file below:

[ToanDN · Accepted solution]

The dormer roof cannot have any part stick out below the main roof.  I would use a roof by extrusion so that I can control the extent of the dormer roof precisely then it joins to the main roof just fine.

Attached is the revised file with 2 options: one roof by extrusion and one roof by footprint.

[ToanDN]

I should have worded it better.  What I meant was: "if you draw a profile of the dormer roof at its front fascia, no part of the profile should stick below the main roof on the profile plane".

[BigPicture045]

To be clear for future readers:

The two gables below are the same. The front face of the gable (yellow outline) cannot protrude into the roof you are joining to.

The above CAN BE joined to the main roof. However if you lower the roof to where the front edge protrudes into the roof you are attempting to join you CANNOT join the roof:

I am glad to have know why this was happening to me. From my point of view this is a design flaw on Revit's software. Most of the time I need the front Gable face to be joined exactly to the main roof face. In order to achieve this the roof has to be manually finessed. 

For such a basic task, I think this should be reworked in Revit's Software.