Attachment vs Overlay when Linking Revit Files

Once you link a Revit or IFC model into your project, you have the option to change the Reference Type to either Overlay or Attachment. What the heck does that mean? If you select one or the other it makes no visible change to your model so it’s easy to ignore. But the Reference Type is actually very important if your Host Revit model gets linked into another model. Your chosen reference type will then determine how that link behaves in the new model. In this blog post, I will explain the difference between Attachment vs Overlay!

Attachment vs Overlay in Revit

So, choosing the reference type of a link determines how Revit will regard that link when your host model is linked into another model.

For example, lets say we are working in Project B and we Link in Project A. If Project A’s reference Type is set to Attachment, when we Link Project B into Project C, Projects B and A will be visible. Basically, Project A will get attached or nested into Project B. See diagram:

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