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:
For the same scenario, if Project A’s reference Type is set to Overlay, then when Project B gets linked into Project C, only Project B gets linked in and Project A gets ignored. See diagram:
From a structural perspective, this is important if you are working with an Architects model who may have a lot of Linked models (such as Site models, repeating floor plans etc.) If the Reference Type of those Links are set to overlay (in the Architects model) then they won’t show up in your structural model.
Similarly, If you are sending your Structural model back to the architect to be linked into their model, you might want to set their Linked models reference type to Overlay so it doesn’t get re-linked as well.
It can be a bit tricky to come to grips with what Attachment and Overlay mean in Reference Types. Hopefully this post has helped you understand the difference between Attachment vs Overlay in Revit.
If you have any questions, or have other tips then please leave a comment below!
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