Note: This topic is for Roombook users only. 
 Roombook supports working with external references (xrefs). 
-  The room quantity calculation for xrefs is performed in the parent drawing. 
-  Roombook recognizes the relevant objects within the xref block and calculates the quantities in the parent drawing. 
- Roombook fully supports working with the AutoCAD Architecture toolset Project Navigator which mainly uses xrefs mechanisms for composing plans. 
Important: External drawings must be closed, if the calculation is done in the parent drawing.