It has been very frustrating to me that ceiling and wall based MEP families do not attach to linked architectural models. This limitation has been dealt with somewhat in Revit MEP 2010 in that some families come now as face based such as swithches and receptacles, but the vast majority of availble families are still wall or ceiling based, so what do you do?
Last night I discovered the answer. Rather than painfully reconstructing the family in a new face based model, you can nest the ceiling or wall based family in a new face based model. You can load the old family into a model, and then using the Component command attache the ceiling based family to the face of the face based family.
There are a few drawbacks. MEP connections do not nest, so after you insert the ceiling based family into the face based family you will need to recreate the MEP connections, and define them properly. They will attach to faces in the nested family. If you want the new family to cut the face you will be attaching it to in the project, you will need to make a new Void extrusion, make sure it cuts only the face extrusion, and move it into place. Here are the steps:
1. Start a new Generic Face Based Family.
2. Under the Family Properties tab click on Category and Parameters. Change it to match what you need, such as Air Terminals, or Lighting Fixtures.
3. Load the ceiling or wall based family into the new face based family. This can be done by clicking on the Insert tab and using the Load Family command, by having the ceiling based family open and clicking on the Load into Project command and selecting the new face based family, or if you don't have any component families loaded, click on the Component command and when the dialog box comes up giving you the option to load a family choosing that and loading the ceiling based family.
4. Use the Component command and place the nested family. You can use either Place on Face or Place on Workplane. Using the Place on Workplane will make so that you can cut a void in the face extrustion any size, and don't need to worry about leaving a bit of face under the nest family.
5. Align the nested family origin with the reference planes in the new family.
6. If you want the family to cut a hole in the face that it will be attached to, create a void in the appropriate place in the face extrusion.
7. Set type parameters as needed such as Default Elevation, Manufacturer, Model, Omniclass, etc.
8. Set up type parameters to match parameters in the nested family, and link them to the parameters in the nested family.
9. If you need to add MEP connections, add them to match the connections in the nested family. You might need to have the nested family open for editing to be able to determine what they need to be
10. Save the new Face Based family, and test it in a project file to make sure it behaves like you expect. Make any needed adjustments.
It only takes 5 to 10 minutes to do this, and can save countless hours recreating families.