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CAD Standards – Defining File Types

Defining the File Types that you will be discussing in your CAD Standard will help those who read it to know what you mean by each term. Without an explanation, they may think incorrectly about your terms or apply definitions that they have used elsewhere.

Example text from a CAD Standard:

There are five different types of files used to generate Construction Documents. These files, when used properly, will expedite the creation and modification of all drawings in the set.

XREF (Background) FILES

XREF files are the basis for all design work. They include the “model” representation of all construction elements in a project, including plan, elevation and section information that delineates what will be built. The general rule is that anything you see at the site after construction will be placed in this type of drawing. All XREF Files are drawn full scale in Model Space. No Paper Space entities exist in this file. Each discipline will create a Model file to contain the information needed for their working “design” drawings. XREF files will be directly referenced to Sheet files. XREF files are located in the XREF folder.


The Sheet file will be used to generate plots, one plot per Sheet file. Each Sheet file will represent only one contract drawing. There will be no multiple generations of plots from one Sheet file. For example, you cannot plot the Architectural Floor Plan and the Reflected Ceiling Plan from the same Sheet file. Sheet files will reference XREF Files and BORDER file.


The Border drawing is drawn full size in Model Space. It is Xrefed (overlay) into Paper Space on the Sheet Files at 0,0. The Border file will be located in the XREF folder. One for each building.

Additional files needed to create the Title Block or Cover Sheet will be located in the XREF folder.


Image files are raster images generated to be attached to CAD files for display. Images may be digital photos or other items needed as key-maps, job photos, etc.

Image files are placed into the Sheet folder and referenced only to Sheet files. They may also be referenced to Model files if needed for reference.


The Detail files contain all the standard details to be displayed on the detail sheets. Details, as with any building element drawn, shall be developed and drawn to full “real” scale in model space, however, the final representation of each detail is inserted as a Block in Paper Space on the Sheet file and scaled.

If you use any vertical products be sure to include definitions for those also, like Constructs, Views and Elements. Don’t assume that people understand the unique nature of each of these and what goes where.

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