When BIM Is BIM: Comparing AutoCAD BIM and Revit BIM


This time of year drives me nuts, with all the political garbage going on. Candidates and parties play on your emotions and fears, rather than dealing with facts and real solutions. It’s no different in the software game—sometimes it’s hard to know what to use, and people get really emotional when it comes to changing their software tools. That fear of change can sometimes cloud your judgment, and cause you to keep falling back into bad habits instead of improving your work process and methods.

A dispute at work made me stop and think…how do I help someone overcome their fear, and understand why we have made the decisions we have about the software we use? The best way to resolve fear is fact—making the information as objective as possible. But opinions are still going to be there, so getting the right information should help you make the right decision.

It all came about in a debate started by one user who insisted that we should be using AutoCAD® MEP over Autodesk® Revit®. Before we get too far, our decision has already been made, but I don’t deal in absolutes. As a company, we made the decision a few years ago that Revit was going to be our preferred BIM platform. If the design team can come to agreement on using the same package across the board—the entire team—then I’m still a huge fan of AutoCAD® Architecture and AutoCAD MEP.

So I decided it was time to lay all of this on the table and highlight the main features of each package. I also want to list what I wish Revit had that compares to what AutoCAD Architecture/MEP includes, and what AutoCAD Architecture/MEP needs that’s already a feature in Revit. Hopefully this will help you make the best decision for your firm and clients.

The Bottom Line

Before we break this down, I’m going to put down one rule. No matter which option you select, the entire team—and I mean the architects, the structural engineers, and the MEP/Process engineers—better be using the same software.

If the project is being completed in Revit, the entire building design team should use Revit. They should also use the same release—if the project needs to be upgraded, then the entire team should go up. Don’t be afraid of updates and upgrades, but keep up with each other. It’s not that big of a deal anymore, and with Autodesk release updates on a more frequent basis, the old “wait three years” rule of AutoCAD upgrades is out the window.

If a project is being completed in AutoCAD as a BIM project, the entire team should use AutoCAD Architecture and AutoCAD MEP. The same rules apply for software version—they should also be on the same release. And if you’re going to compare apples to apples, you damn well better be using Project Navigator. Anything else is not a fair comparison. Remember that both platforms are forward compatible, not backwards. This is usually one of the biggest hurdles when different firms are involved in the design, but it has to be resolved.

One interjection for the process/oil and gas folks: you can include AutoCAD P&ID and Plant 3D in here as well. It’s not a big deal to bring in an AutoCAD Architecture structural model and/or MEP models. There’s a ton of similarities. Keep in mind that when you’re using the Plant packages, you are always tied to a SQL database and you MUST work in their project environment.

The same rules apply to the civil/site users. AutoCAD® Civil 3D® has its own document management system so it’s better to stay all in that platform. It’s pretty easy to convert Civil 3D files over into Revit sites, as well as to use them in an AutoCAD Architecture/MEP project. So it’s OK to leave them out of the equation for now. We’ll save all of this for a different story.

As far as cost difference, there really isn’t much difference here. With the suites and the upcoming Autodesk subscription/rental model, the cost difference is so minimal on the actual software, it’s a moot point. The same rule applies to the hardware—both software sets have the same requirements because you’re working in 3D model land. You need a real BIM machine, so don’t skimp here. Get as much RAM as you can, at least 16GB, and make sure you have fast network and Internet connections. Stay away from on-board video and get a good graphics card. The fastest hybrid/SSD hard drive is the way to go as well, but you’ll always need a lot of disk space now.

One item you can’t ignore—if a client requires you to use a specific BIM software, then use it. If they are requesting an older version (like the request for Revit 2010 or AutoCAD MEP 2012 we keep getting), that argument and requirement is out the window now, with the current maintenance and licensing rules. Don’t be afraid to educate your client on this—if they’re going to put the CAD/BIM requirement in, then they have to be able to keep up with the rules themselves.

Here’s something subjective—if a client requires AutoCAD, that is not an excuse not to use Revit or AutoCAD Architecture/MEP either. You should be using these tools because both are a VAST improvement over plain AutoCAD, especially in the work process and methods area. You can always dumb down a Revit model or AutoCAD MEP set of drawings. It’s actually gotten a lot easier, especially when comes to exporting to specific sets of layer and annotation standards.

The Commonality

This is the safe part. Both programs, for architectural, structural, and MEP users, have a lot in common. You should take comfort that all of these tasks and tools are what make the programs a better solution than 2D CAD, so you can’t go wrong.

3D Modeling

Both platforms generate 3D models, allowing for predefined objects and components. This includes walls, floors, roofs, and opening components such as doors, windows, and curtain walls. The models are then used to create “2D” plan, section, and elevation views. The work process is a little different, but the outcome is basically the same.

Figure 1: Revit model

Figure 2: AutoCAD Architectural model

Drafting – Details!

AutoCAD Architecture/MEP and Revit both include 2D detailing tools that allow you to draft over a model view and add clarity to the view. Right now, it’s not feasible to model every brick and block, add every nut and bolt, and detail a model down to a finite degree—if this were the case, then we’re just not getting paid enough to do that. The detailing tools do allow you to work from some automated drafting tools such as laying out brick coursing, indicating bolt locations, adding supports, and more. The focus of these tools is heavy in architecture and structure, but lighter on the MEP side. This is due to the amount of variation that can occur with the MEP components, but are a lot of commonly used components included in both packages.

Figure 3: Revit detail component family

Figure 4: AutoCAD Architecture detail component library

When it comes to equipment models and content, you can’t go wrong either way. Both programs have been around long enough that placeholder content is extensive, in all disciplines. This includes architectural wall construction types, piping libraries, distribution equipment, and more. They also allow for reduced detail level of a 3D model, while allowing a more detailed 2D view to be applied to all elevations of a view. But you can also just use a detailed 3D model and skip the 2D part altogether. In either program, you have tools that allow you to import detailed 3D models from vendors and outside sources and use them as a basis of design for your project.

View Display and Documentation

You can adjust the detail level in a view—from single line and conceptual visualization to fine levels of detail—using display configurations and detail levels in the programs. For example, a wall can be told to only show its outer boundary in a more coarse level of detail view, but then turn on the internal components and materials in a fine level of detail. They’re even smart enough to lighten themselves and reduce detail when used as a background for a MEP model. And in the MEP model, you can choose between single-line and double-line display of linear objects such as duct and pipe. This builds on the concept of creating a model and using it throughout the design process, as opposed to the older method of trashing conceptual drawings before moving into design development and documentation.                 

Figure 5: Revit fine detail view—brick/block wall         

Figure 6: AutoCAD Architecture—high-detail display configuration

In terms of documentation, both tools include tagging and label tools that extract information from the object and are used to identify the object. If the object properties change, the annotations update themselves. Automatic dimensioning is also available, and all annotation objects can resize themselves based on the view’s scale for the sheet.

Object Data

Both platforms include data fields in the form of property set definitions (AutoCAD) and parameters (Revit) that can be associated with the objects in a model. The data fields can include static values that are usually text-based entries, and automatic properties for an item’s dimensions and engineering design properties.

Figure 7: Revit duct with parameters

Figure 8: AutoCAD MEP duct with parameters

The data fields can be used to generate schedules, which are tables used as a report in a construction documentation set. While there are methods that allow a user to bring in external spreadsheets that have been the common form for these tables in the 2D world, this is one of the big work process changes that architects and engineers must overcome. In both cases, it’s better to begin by associating the data in the model, and then export the data out to a spreadsheet. The data can be imported back into the model as adjustments are made.

Figure 9: Revit light fixture schedule

Figure 10: AutoCAD MEP light fixture schedule

Design Calculations

Most of the calculations being performed in a spreadsheet now can most likely be performed in a model. But when you separate this information using the traditional method, you’re adding steps to your own workflow. It actually is better to start with the model and work outward, which means that engineers and architects, Heaven forbid, may have to actually open a model file and work in it. Oh, the horror… But again, this eliminates steps and is also where most communication breakdowns occur in a project.

For the calculations that have to be performed outside of a model, both tools allow for integration with external design applications. In some cases, you’re deriving a starting point from a model such as with an energy analysis for the model. In other cases, such as with the design of an HVAC system, you would perform the initial design outside of the model, but then add the results by building a model based on the results. Both applications include duct, pipe, and electrical sizing routines, which all still need some work. Autodesk is headed in the right direction here, but the workflow is still not conducive to start in the model.

Materials and Rendering

To get more out of the model, both platforms include material libraries for rendering. The materials can be applied from the highest level (such as the object system, the wall style, etc.) all the way down to an override to a specific element. Both tools allow export of the model to a rendering application (such as 3D Studio) or cloud-based rendering service. The idea here is to use the same model throughout the process, from conceptual design down to the construction documentation.  We’re seeing more companies include rendered 3D model views as part of their deliverable. This is great, since the documentation set is really about providing the clearest possible directions to the contractor and owner for how the structure and its components should be built.

Figure 11: Revit Material Browser

Figure 12: AutoCAD Architecture/MEP material definitions

Model Interoperability

There is some limited compatibility between the applications. AutoCAD BIM models can be exported using IFC tools, which allow the user to pre-assign Revit categories to objects. Specific drawing file property set definitions can also be associated with the geometry and read within the Revit model. But that’s as far as it goes. Items such as duct or pipe don’t convert to native Revit objects, so in reality, they’re just 3D objects with a little information associated.

Clash Detection

We continue to see the owners evolve in their expectations, and more of them no longer accept change orders for clashes and conflicts in the design. They’re aware that design tools include coordination and interference detection tools. Both AutoCAD Architecture/MEP and Revit include these tools out of the box, but designing from a model also allows both the designer and the contractor to use external applications such as BIM 360™ Glue®, Navisworks®, Solibri, and more to check for these errors.

Figure 13: Revit interference check

Figure 14: AutoCAD MEP interference detection

Regardless of the platform, all of these tools represent the evolution of design away from a 2D drafting mindset. The days of having to customize AutoCAD to draw lines faster and draft more efficiently can’t come close to matching the efficiency of the “do it once, use it many” modeling workflow. It also dramatically alters the roles of the traditional design firm. The professional has to be more engaged in the design process, but at the same time, the day of redline drafter is gone. The technician or designer has to understand basic design concepts and be capable of making design decisions without the professional’s engagement…but simply their approval.

Now That We Know This…What’s Next?

So here’s where I’ll break this up into parts. The next installment in the series is on the AutoCAD Architecture/MEP, Project Navigator platform. We’ll dive into the key features of the package, and what this program has that I wish Revit had. Following that, we’ll cover the key features of Revit, and what it has that I wish AutoCAD Architecture/MEP had.

Both packages do a great job when it comes to Building Information Modeling, and I don’t like having to play favorites. It’s important to make sure you know why you would select one of these tools, so take the time to review the facts first, and get what fits your design process—and client needs—the best.