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Revit: Everything that MEP Contractors, Engineers and Detailers should know

AutoCAD for drafting and creating basic geometry, and Revit for creating geometry enriched with real-life information, supporting the ‘i’ in BIM

Published: 19/03/2019

Country: United States

Revit and AutoCAD, both are the star products of Autodesk and popular CAD platforms across the construction industry. AutoCAD is extensively used for creating basic geometry, whereas Revit is leveraged for creating geometry enriched with real-life information for supporting the “I” in BIM.

AutoCAD and Revit, if compared, have several differences, and may be that is the reason why organizations use both of them for different purposes. For years together, Revit has been the design platform of choice for architects and engineers. But, though Revit has a very rich history in architecture; increasing number of MEP contractors, engineers and detailers have swiftly moved to the platform in last few years.

Let’s understand the reasons why Revit is different from AutoCAD, is it really better, and how does it support changing workflows in construction?

Revit stability to work side-by side

We all know that evolving needs of end users, the urge to become cost effective and attaining process efficiency is actively changing the game of construction. To attain all these, it has become more than mandatory for architects, engineers and contractors to work side by side. Revit prominently offers the kind of stability required for this pattern of working.

Revit is developed especially to manage graphically intense 3D models. 

Revit Model

A single Revit model can contain minutest architecture, engineering, MEP detailing, schedules, spool and fabrication information. Upon further development/change in the model; existing spools, schedules and everything else gets automatically updated by Revit without requiring user intervention. 

AutoCAD was developed as 2D line drawings software.

AutoCAD File

A single AutoCAD file may contain details of ductwork on a 2D background in wireframe, whereas material schedules and spools would be available in a separate file altogether. So the slightest change in the drawing, would lead to mandatory remaking of schedules and spools. AutoCAD does not give any notification about a spool or schedule being outdated.

Nothing wrong, if we say that Revit offers far more stability to handle humongous 3D models and also facilitates ever evolving workflow of construction projects.

Revit work-sharing 

Shrinking deadlines and compressing budgets have changed the linear processes that started with architect completing the design to pass it on to the engineering team, and the resultant output is then handed over to the contractor to begin the construction.

But this no more is the reality in this age of shrinking budgets and project timelines. Today, what architects, engineers and contractors desire of is their involvement in the project at the earliest possible point. As in on a project site, you can find a duct contractor installing ducts while the piping contractor is installing pipes at the same time. An ideal scenario is where different contractors are allowed to work together in the same model, which calls for work-sharing.

Revit offers the work-sharing function which empowers users to open and work in the same model at the same time, through a local network or even via the cloud. It propels a situation where on one hand where architects are completing the overall design of the building, the engineers can kick start designing the MEP systems for some of the floors, and contractors start detailing the mechanical room.

Floor Information Modeling to Building Information Modeling

BIM (Building Information Modeling) contains functional components that provide data/information not only about the size; but also the capabilities of these functional components upon getting connected as a system. Revit lends itself for BIM. Revit platform looks at building elements as parts of a complete building including views of floors and systems, permits, prefab and functional sheets, different rooms, and schedules with materials and equipment.

Floor Information management is the maximum that can be expected out of AutoCAD. Usually AutoCAD projects consist of multiple DWG files. They display a complete floor of MEP overlaying a 2D architectural or structural background. MEP systems are just a collection of blocks and not connected systems, and MEP components do not interact with 2D background or any other parts of the building without current DWG. None of the DWG files connect with other DWG files in AutoCAD, so in case a riser is moved, all floor drawings will have to be opened to be edited.

Revit inter-connectivity adds functionality to design

The model and system concept, are it seems the reason why architects and engineers are so much inclined towards Revit as the platform of choice. A Revit model, even when functional, keeps analyzing loads and flows on a system. It also offers routing and sizing options. Revit is popular for its interconnectivity, which further add the functionality to the design; which is not possible while using AutoCAD.

Enlisted are some of the rules that need to be played by in order to reap these benefits:

• Revit does not look at “pieces”, instead looks at “connected systems”, making it mandatory for MEP systems to have a inception and an end point; i.e., ventilations systems with AHU and a VAV.

• Revit includes a lot of information for creating a linked functional system including size, flow and power requirements.

• Upon connecting two objects in Revit, maintaining connectivity between them while they are moved around or re-sized is taken care by Revit.

• Concepts of walls, floors, ceilings and many such more are clear to Revit, i.e., floor based components such as a pump is always seated on the floor. It means when the floor moves – the pump moves as well. Grills and diffusers will automatically move when the ceiling grid is moved. 

Multiple, user-definable, views and schedules of a single entity that are connected is also one of the main contributors to the popularity of Revit. Displaying a VAV unit from a ventilation system in multiple views, spool sheets and also as part of an equipment schedule is convenient. Talking about changing the properties of VAV, such as manufacturers can be done through the graphical or the schedule view. Whether the properties are changed or not; the entire model is updated accordingly and Revit will maintain the system connectivity.

Revit: The single model environment

Usually, construction projects incept in form of Revit models by architects and site planners. Then AutoCAD DWG ‘backgrounds’ from the Revit model are handed over to MEP contractors. But this process has several disadvantages, including

• Time and efforts required to annotate and document the Revit ‘Views” in order to make the created DWG files, useful. This is followed with the efforts that are to be put in by the engineers to communicate information to help contractors redraw what the engineer has already modeled.

• Working in AutoCAD requires opening, editing and closing multiple DWG files for a project, which are not connected and unaware of changes made in the file. However, organizing, naming and keeping files connected are a convenience when working in Revit. It allows a single model of the entire building to be opened. To an extent that Revit allows mechanical equipment and plumbing fixtures to be connected not only on each floor, but to the risers and other floors as well.

• Chances are very thin that the model is finished by the time MEP contractors start their work. Upon project progression, additional DWG revisions are introduced which inevitably require MEP contractors to compare “before” and “after” DWG files to identify the changes made.

• DWG files are not information intelligent to be imported as functional Revit objects. Don’t forget that Revit models can be pulled down to be DWG files, but DWG files cannot be smartened to become Revit models. 

All these challenges put together call for a single model environment, which can contain architecture, engineering and MEP components. Revit offers a single model environment. It means just like various disciplines contribute to the design and construction of a single construction project, similarly Revit provides a single platform which meets all the various requirements of various stakeholders across the construction project lifecycle.

With the model progressing ahead, structural and MEP engineers also have the liberty to add their expertise and knowledge to the same existing model. They can utilize Revit’s in-built design, engineering and analysis capabilities, and does not require converting or exchanging any DWG files as required information is managed through a single Revit model.

Should we compare both of them?

Both of them are used extensively by architects, engineers, and contractors for generating or tracking construction documents. Apart from the differences mentioned above, there are a lot of same features too, known by different names, which AutoCAD and Revit share. Blocks in AutoCAD are families in Revit, whereas Layers are Systems in Revit. Ideally they serve the same purpose, but while depending on entirely different concepts and workflows.

Hi-Tech CADD Services is your trusted BIM partner; supporting the design requirements for contractors, architects, engineers and MEP consultants through BIM solutions across USA, UK, Europe and Australia.

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