I know I put that CAD file in here somewhere

I know it's hard to believe, but we still use CAD files, shocking isn't it? Even though civil, landscape, and other consultants participate in the BIM process, they don't always work in Revit, therefore sometimes we link in dwg's from them. And that's OK. We're still in a transition stage in the industry and may be in this stage for a little while longer. In the meantime there are some nuances when it comes to linking and viewing dwg's in Revit.

Nested vs Direct Link

Of course you know you should always link dwg's instead of importing, but maybe you didn't know it's possible to view nested dwg's. Let me explain. If the architect links a dwg provided by civil, landscape, or even a furniture vendor into the architecture model, and then the architecture model is linked into a different Revit model, you have a nested dwg. Whomever the beneficiary of this linked model now has the ability to view the nested dwg without having to directly link the dwg into their model. Please be aware that if the architect links the dwg to the "Current View Only" option, the "Linked View" in the RVT Link Display Settings dialog will have to be set to that specific view.

The downside to Nested Links

The downside to nested links is you can't control the dwg layers as easily as a direct link. Direct linked dwg's allow you to query the object and either hide or delete layers from the Import Instance Query dialog. In a nested dwg scenario you can still control the layers, but you have to do it through the RVT Link Display Settings> Import Categories tab. In this scenario you can't query the lines so it helps to know the layers that make up the line work in the dwg. 

 In the end either method works. There are advantages and disadvantages to both. The next time you have to link a dwg into your model, decide as a team how you approach it. This potentially affects all team members regardless of discipline. Discussing this up front on a team level will yield a more consistent work flow which improves your process. 

Exporting to CAD

For the most part exporting is as easy as 1-2-3. However there are a few things you should be aware of before exporting. First of all you should make sure the Export Layers txt file is in order. Meaning if you haven't created one for you office, now's the time. It's not too difficult really, all you have to do is follow some basic rules. Revit uses a txt file to map categories and subcategories from Revit to layer names and color numbers in Acad. The format is as follows: Category (tab) Subcategory (tab) Layer name (tab) Color number (tab) Cut Layer name (tab) Cut color number. If there isn't a subcategory then you simply skip it. This is an image of the AIA export layers txt file that comes with Revit. You can always use this one to get started and just save as to create one specific to your office standards. Once you've created the txt file, all you have to do is map the file location in the import/export settings. You do this by clicking the file drop down menu and selecting Import/Export Layers Settings. From there choose the format; DWG/DXF, DGN... Once you choose you can load the txt file into your project and you'll be able to see the Category and Layer name along with the cooresponding Color ID Number. The cool thing about this txt file is you can save it on your network somewhere and path it to your Revit template so you'll never have to do this again.