Datasheet

File Types and Families
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System and Hosted Families (.rfa)
As mentioned earlier, a Revit model is based on a compilation of items called
families. There are two types of families: system families and hosted families. A
system family can only be found within a Revit model and cannot be stored in a
separate location. A hosted family is inserted similar to a block (or cell) and is
stored in an external directory. The file extension for a hosted family is
.rfa.
System Families
System families are inherent to the current model and are not inserted in the
traditional sense. You can only modify a system family through its element prop-
erties within the model. The walls you’ve put in up to this point are system fami-
lies, for example. You did not have to insert a separate file in order to find the
wall type. The system families in a Revit Architecture model are as follows:
Walls
Floors
Roofs
Ceilings
Stairs
Ramps
Shafts
Rooms
Schedules/quantity takeoffs
Annotation items
Views
System families define your model. As you can see, the list pretty much cov-
ers most building elements. There are, however, plenty more components not
included within this list. These items, which can be loaded into your model, are
called hosted families.
Hosted Families
All other families in Revit Architecture hosted in some way by either a system
family or a level. For example, a wall sconce is a hosted family in that, when you
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