If your SketchUp model contained any geometry before the import, the imported CAD geometry is grouped automatically.
Make sure the CAD geometry is a single group.If the size is incorrect, the Tape Measure tool also enables you to scale the entire model so that the dimensions are correct. Choose an entity with a measurement you know and check its size with the Tape Measure tool ( ). Check the size of the imported CAD geometry.Here's a recommended workflow for getting an imported CAD file ready for modeling in SketchUp: For details about installing extensions, see Adding Extensions to SketchUp This extension can clean up terrain and CAD files for you by simplifying curves and closing gaps. If you need to use your CAD geometry, however, check out the Edge Tools 2 extension by user ThomThom. If you've imported a floor plan, for example, drawing over a floor plan to create a new model is easier than hunting and pecking to find and fix all those gaps.
Also, imported CAD geometry is likely full of gaps that need to be closed to create faces. When in doubt, re-creating the model with SketchUp's native drawing tools typically produces better and more consistent results than trying to manipulate the imported CAD geometry. Tip: Why use the CAD file as a reference? The main reason is because CAD geometry is often way too complicated to create a useful SketchUp model. Whether you've never worked with a CAD file imported into SketchUp before or have lots of experience importing CAD files, the tips and examples in the following sections can help you quickly start modeling with your file in SketchUp. Hunting down all these little gaps can be tedious - unless you know a few tricks explained in this article.
Therefore your doors and windows don't exist but there are openings in the walls where they would be. I find its quicker to just make an opening. Su does not like windows and doors although sometimes you can un-group, make them a solid addition and they work. Unfortunately the process is not a straight conversion.