BIM, With a Side of 2D (1-2-3 Revit Tutorial)

Revit and AutoCAD can work together to support today's architectural workflows. Here's how.

For more than a quarter of a century, AutoCAD software has been one of the favorite CAD packages of designers around the world. Given its popularity, most building teams using building information modeling (BIM) are also using AutoCAD in some fashion. This month’s “1-2-3 Revit” examines various ways that AutoCAD is being used on BIM projects.

About AutoCAD
AutoCAD was introduced by Autodesk in 1982. Unlike most other CAD packages at the time, AutoCAD was PC-based -- therefore much more affordable and easier to use than its rivals. As a result, it gained widespread popularity for documentation, drafting, and also for design work.

AutoCAD software lets users document and communicate ideas clearly and efficiently. And it lets users customize and configure the software to meet their specific needs, or users can select from thousands of third-party add-ons and applications.

The software program -- currently in its 23rd release -- is one of the most commonly used applications within the building industry, translating into an abundance of both AutoCAD-trained designers and AutoCAD-based designs. The native file format of AutoCAD (DWG) has become a popular means of sharing CAD data and there are said to be at least two billion drawings that exist in DWG format. With numbers like that, it’s not a surprise that even the most sophisticated BIM teams also use AutoCAD -- especially during the documentation process.

Using AutoCAD in a BIM Workflow
Here are some common reasons that BIM teams incorporate AutoCAD software into their process:

• For drawing production on an active project, allowing organizations to take advantage of existing CAD drafting staff or contractors who have AutoCAD experience.
• For the reuse of AutoCAD-based drawing libraries and legacy data, such as standard details.
• For making minor changes to drawings from an archived Revit project (when it’s easier to just change a few drawings in AutoCAD).
• For final documentation delivery at the end of a project. Many firms will convert and deliver documentation sets in AutoCAD format, to meet contract requirements and/or to accommodate partners or clients who are using AutoCAD.

The most common use of AutoCAD by a BIM team is for drawing production. Building design models created with BIM software such as Revit Architecture are exported and xref’d into AutoCAD for detailing. In this manner, the details created using AutoCAD are still based on the highly accurate Revit design model. Once the AutoCAD drawings are complete, they are imported back into the Revit-based software to keep the project drawing set centralized and coordinated. Linking the AutoCAD details to Revit ensures that if the AutoCAD details change, the Revit documentation set is updated. This mixed-mode drawing production strategy is particularly useful for the portions of the Revit-based design that are fixed -- minimizing the chances of having to manually update AutoCAD-based details.

Many firms also use AutoCAD early in the conceptual design phase and then import the resulting 2D sketches or 3D models into Revit as the basis for further design. In fact, the use of AutoCAD for conceptual design is a growing trend, as AutoCAD is a good tool to use when the building form is still emerging and you need to play with design ideas in a general “prebuilding” way.

Typical Revit/AutoCAD workflow
Below are the basic steps for using both Revit Architecture and AutoCAD on a project. Similar workflows and steps can be used for Revit Structure and Revit MEP.

Conceptual design

• Create a conceptual design (in 2D or 3D) in AutoCAD.

• Import the AutoCAD file into Revit Architecture and use that geometry as the starting point for your design in Revit.

Production documentation

• Use Revit Architecture to design the building.
• Set up documentation sheets for the project in Revit Architecture and begin detailing the building.
• Determine what details to reuse from your existing AutoCAD library and/or what sheets will be worked on in AutoCAD. Once that’s determined, create the underlying detail views in Revit Architecture.

• Export selected Revit Architecture views or sheets to DWG format for AutoCAD users.
• Text, annotations, and other detail elements are then added in AutoCAD, but they’re based on the referenced DWG files that were exported from Revit Architecture – that is, the original building information model geometry.

• When finished, the AutoCAD drawings are linked back into the appropriate Revit views. Revit maintains a live data link to AutoCAD drawings via the File Link Manager, which can be used to manage and update the referenced AutoCAD files.

Revit and AutoCAD in Action
Kobi Karp Architecture and Interior Design (KKAID) has participated in the completion of more than $10 billion in commercial, residential, and mixed-use properties around the world since its founding in 1988. Headquartered in Miami, the firm has the expertise to take projects from site planning through project build-out. The firm’s entire design staff (65 in total) uses the AutoCAD Revit Architecture Suite.

An AutoCAD user since 1996, KKAID chose Revit as its BIM platform in part based on the software’s interoperability with AutoCAD, and users rely on AutoCAD to support their documentation process. “On a typical project, we use AutoCAD for approximately 10-20% of our drafting,” reports Christian Berthin, director at KKAID. “And for very large projects, that percentage goes up.”

For example, one of the firm’s recent projects was the 10-tower, 5 million ft² residential complex for Etihad Airways in Abu Dhabi. The 4,700 residential unit complex will provide housing for Etihad Airways. “This project had over 1,000 drawings, and we relied heavily on AutoCAD for construction documentation,” explains Berthin. The firm used Revit Architecture for its design. The Revit model was used for visualizations, to create plans and sections, and to produce drawings of complicated sections such as stairs. “Then we used AutoCAD for much of the detailing,” says Berthin. “AutoCAD is an industry leader and we couldn’t have done this job without both Revit and AutoCAD.”

Summary
The combination of the Revit platform and AutoCAD represents a pragmatic, production-proven solution for design and documentation. The interoperability between the Revit platform and AutoCAD enables firms to take advantage of the abundance of AutoCAD-based data and AutoCAD-trained staff -- and still realize the benefits of BIM.