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Autodesk AutoCAD and Autodesk Revit

CAD and BIM Productivity Study

Autodesk AutoCAD and Autodesk Revit—CAD and BIM Productivity Study I 2


Nearly 30 years after Autodesk® first released AutoCAD® software, many architects are still successfully using the lines, arcs, and circles of CAD to represent building objects. AutoCAD is used by thousands of architects and engineers every day on projects of varying complexity and continues to be a popular format for creating and sharing construction documents. At the same time, though, the expansion of Building Information Modeling (BIM) in building design and construction is unrelenting, and firms large and small are exploring BIM workflows, using Autodesk® Revit® software.

Building Information Modeling (BIM) is more than software—it is a process that begins with the creation of an intelligent 3D model to help capture, explore, and maintain planning, design, construction and operations data. The information in the model remains more accurate, accessible, and actionable throughout the lifecycle of the project and can be used for simulation, analysis, collaboration and com-munication in order to better inform decision making for building and infrastructure projects. Accordingly, transitioning to a BIM process is more than a soft-ware upgrade—moving to BIM, whether for a project or across a practice represents a change in business process that can be transformational.

Implementing BIM across a firm starts with vision and leadership, but it is ultimately driven and successfully carried out through effort on the “shop floor” by the individuals who will apply BIM in their day-to-day execution of projects. This study examines just one component of the move to BIM—the experience of the architect in creating a completely coordinated set of construction documents. This study provides details on Revit® design tools and processes and quantifies the productivity gains they provide over traditional AutoCAD drafting techniques when it comes to designing and documenting an actual building project.

About this study The CAD and BIM Productivity Study was conducted by independent contractor David Cohn in June 2014. The subject of this study is the re-creation of ten sheets of an actual set of construction documents that were used for for a two-story addition to a hospital. The original drawings for the hospital were created in 1979 using traditional board drafting. In this study, those drawings were re-created using both Autodesk® AutoCAD® 2015 and Autodesk® Revit® 2015 software. The study addresses only the pro-duction of the construction documents and did not include the actual building design component. Results therefore focus solely on the productivity difference between using Revit and AutoCAD to produce construction documents.

The study was comprised of ten tasks that represent typical operations faced by architects during the creation of a set of construction documents. The benchmark of the study was the time required to complete each task with AutoCAD 2015 and Autodesk Revit 2015.

Summary of resultsAlthough the time required to set up office standards and produce the initial floor plan drawings was approximately the same using Revit or AutoCAD, Revit quickly proved to be a more productive environment. While the user would have to spend hours to create each drawing anew in AutoCAD, additional floor plan, elevation, section and sched-ule views were generated in Revit in minutes. As the project progressed, changes to any aspect of the building in Autodesk Revit immediately propagated through all of the documents whereas when working in AutoCAD, even a minor design change necessitat-ed manual changes to multiple individual drawings.

While Autodesk Revit automatically managed the coordination of each change, changes to the drawings in AutoCAD required manual coordination to prevent documentation errors.

Introduction



10 Tasks1 Floor Plans

Creation of fully dimensioned architectural floor plans for the first and second floors of the building 6

2 Elevations Creation of all exterior building elevations 10

3 Reflected Ceiling PlansCreation of reflected ceiling plans for the first and second floors of the building 12

4 Building Sections Creation of cross sections through the entire building 13

5 Construction DocumentsCreation of the ten sheets of construction documents and placement of the various drawings onto those sheets 14

6Large Scale Details Creation of a selection of five detail views, including an enlarged floor plan view, a section through a typical stair, and large scale details showing typical wall conditions at the floor and ceiling 16

SchedulesCreation of complete room finish and door schedules 187Project ModificationModification of drawings necessitated by late changes in the design of the building 208Coordination and Publishing Coordination and publishing of the ten sheets of construction documents 229RenderingsProduction of high-resolution renderings showing the exterior of the building and the interior of a typical patient room 23

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Productivity Autodesk Revit 2015 vs. AutoCAD 2015

27hr: 43 min



The CAD and BIM study consisted of the re-creation in both programs of ten sheets of construction documents that had originally been produced using traditional board drafting. The building used as the basis for this study is an actual two-story hospital addition built in 1979. The study was broken down into ten discrete tasks:

1. Creation of fully dimensioned architectural floor plans for the first and second floors of the building

2. Creation of all exterior building elevations

3. Creation of reflected ceiling plans for the first and second floors of the building

4. Creation of cross sections through the entire building

5. Creation of the ten sheets of construction documents and placement of the various drawings onto those sheets

6. Creation of a selection of five detail views, including an enlarged floor plan view, a section through a typical stair, a typical wall section, and large scale details showing typical wall conditions at the floor and ceiling

7. Creation of complete room finish and door schedules

8. Modification of drawings necessitated by late changes in the design of the building

9. Coordination and publishing of the ten sheets of construction documents

10. Production of high-resolution renderings showing the exterior of the building and the interior of a typical patient room

Each task was timed using both AutoCAD 2015 and Autodesk Revit 2015.

The Study in Detail



When creating a set of construction documents, most architects begin with the floor plans. Before starting this working using a CAD program, however, one must develop the styles and symbols that will be used throughout the project. For example, the hospital required a number of objects (such as walls, doors, windows, columns, and beams) as well as symbols (such as tags used to identify doors and rooms).

In AutoCAD, all of these objects and symbols had to be manually created using lines and arcs to represent the doors, windows, and beams. These were then saved as blocks. In many instances, a single dynamic block was created that could then be updated to represent different sizes of the same object (such as doors of different widths) or to store different views of the same object (such as top, front, and side views). Elements such as room identification tags were created as blocks with embedded attributes.

Later, when these blocks were inserted into the drawings, data such as room name and room num-ber could be entered and stored as part of the block instance so that the data could subsequently be extracted and used to create the necessary schedules. Whenever possible, custom components and even hatch patterns were placed on tool palettes so that they could later be added to drawings by simply drag-ging and dropping them into the design.

While most objects and symbols had to be created from scratch in AutoCAD, Revit comes with a library of thousands of predefined parametric components or families. These can simply be loaded and used as is or may be easily customized to better reflect the unique requirements of the hospital project.

Once the styles and symbols had been developed, the actual creation of the floor plan drawings could begin. The hospital consists of two main floors of approximately 14,500 square feet each plus a partial basement level of 10,000 square feet, and a 7,000 square foot single-story wing. The structure is cast-in-place concrete. Exterior walls are brick veneer on steel studs. Interior walls are primarily gypsum wall-board on steel studs.

Figure 1. A typical plan view of a door symbol defined in AutoCAD 2015 as a dynamic block. The block also includes attributes to additional data that can subsequently be extracted to create a door schedule.

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Floor Plans

Figure 2. To create custom wall types in Autodesk Revit, the user can begin with existing components and easily modify them as needed, or create new families from scratch.



Task 1 – Floor Plans

Floor Plans in AutoCADWhen working in AutoCAD, one typically draws objects in two-dimensions, essentially duplicating on the computer what an architect or engineer former-ly drew by hand. In AutoCAD, a base drawing was initially created showing the structural grid and the existing buildings. These were saved as external references so that they could be easily reused in multiple drawings.

The hospital floor plan was then created using simple line entities to represent the walls. Working in 2D helped save some time, since only the line work that would actually appear on the construction docu-ments needed to be drawn. But since AutoCAD has no way of recognizing that a particular line represent-ed a wall or a window, it is up to the user to create entities on the proper layer or using the proper line style in order to differentiate the purpose of each line. In addition, line work representing walls must be cleaned up manually. For example, when two walls intersect, the user must manually trim the line work at the intersection. When a door or window is inserted into a wall, the user must first draw the jambs, then trim the line work to create the opening, and finally insert the door or window.

Since the typical two-bed patient rooms consisted of a standard core that included individual toilet rooms and closets, these were drawn one time, saved as a group, and then copied to create each pair of rooms. This helped save significant time and illustrates the power of using a CAD program versus manual drafting. After drawing the main portion of the first floor, that line work was copied and used as the basis for creating much of the second floor plan drawing, again helping to save a significant amount of time compared to manual drafting.

Figure 3. A considerable amount of time was saved by first drawing a typical two-bed patient room in plan view and then copying it to create pairs of rooms.

Floor Plans in Autodesk RevitBecause Autodesk Revit is software for Building Information Modeling, architects actually model the building in three dimensions. The components in Revit software’s extensive library are 3D representa-tions of actual building components. For example, when you draw a wall, the software creates the wall in 3D, extending from the floor level upwards to a specified height. Similarly, when you insert a door into a wall, the resulting door appears in the plan view, but is also a more accurate representation of the door within the context of the 3D building model.

Revit software’s library includes several wall families that could be used without any modification to represent the hospital’s interior walls.

But since the exterior walls included both the brick veneer and an exposed concrete spandrel beam, this component had to be created as a custom wall family. Similarly, the horizontal sliding windows with integral air-handling units also required the creation of a custom window family. Both of these unique objects required additional time to create in Autodesk Revit before they could be added to the building model. But modeling them as parametric 3D objects, helped to save time later in the project when these objects would also appear in the building sections, elevations, and details.




To create the floor plans in Autodesk Revit, a single typical two-bed patient room was modeled and mirrored, and then the pair of rooms simply copied to create all of the remaining two-bed patient rooms. The second floor was then created by copying much of the first floor to the second level and then making the necessary modifications. As work progressed, controlling parametric dimensions were added and locked so that the walls and various family compon-ents would remain properly placed. Unlike AutoCAD, Autodesk Revit works with objects representing intelligent building components that understand their purpose and behave accordingly. For example, when two walls intersect, the software cleans up the line work automatically. When you insert a door or window into a wall, Revit automatically creates the

necessary opening and cleans up the line work.As a result, it took considerably less time to create the walls in Autodesk Revit than to simply draw the line work geometry in AutoCAD.

Figure 4. Autodesk Revit works with objects that represent actual architectural components, so the typical two-bed patient room created in plan view is actually modeled more accurately in 3D.

Comparing this task in AutoCAD versus RevitBecause every component of a building must be modeled in 3D, Revit requires more time up-front than AutoCAD does. For example, while they were not required for the floorplan task, the actual floor and roof slabs had to be created in Revit so that they would appear later in building sections. Sim-ilarly, although the basement floor plan would not be included among the drawings being re-created for the study, a portion of the basement level had to be modeled in Revit so that it would appear later in the resulting building sections. The surrounding terrain also needed to be modeled so that when building elevations and sections were generated later they would show the proper topography.

Similarly, stairs and ramps had to be modeled in 3D for these same reasons; they could not simply be drawn in 2D. While modeling these additional ele-ments was accomplished more quickly using the tools in Autodesk Revit, their creation added time to the floor plan task that was not necessary when creating the two-dimensional floor plans using AutoCAD.

After creating the floor plans in both AutoCAD and Autodesk Revit, dimensions, annotations, and tags were added. Thanks to the parametric dimensions already used to control the location of objects in the building model, many of the dimensions were already present in Revit and could simply be con-verted into permanent dimensions. Since Revit is purpose-built for architecture and understands how architectural drawings are typically dimensioned, the dimensioning tools make it easier to add any additional dimensions that may be required. By comparison, since AutoCAD is designed to be a general purpose drafting program, additional effort was required to create appropriate dimension styles and to then add the necessary dimensions to the AutoCAD floor plans.

It took 21.5 hours to complete the two floor plans using AutoCAD, compared to 20.8 hours to com-plete the same first and second floor plans using Autodesk Revit. These results are detailed in the following table.




Subtasks CAD BIM

Create structural grid and place columns 1.5 1.0

Create outlines of existing buildings 0.25 0.5

Create custom windows and doors 1.0 3.0

Create custom wall types n/a 0.8

Create first floor 11.75 10.5

Create custom tags 0.5 n/a

Add dimensions and tags to first floor 2.5 0.35

Create second floor plan 2.25 1.25

Add dimensions and tags to second floor 1.75 0.15

Add floor and roof slabs n/a 1.25

Create basement level n/a 0.5

Model topography n/a 1.0

Model stairs and ramps n/a 0.5

TOTAL TIME: 21.5 20.8

Figure 5. The second floor plan, as created using Autodesk Revit.

Task 1 – Floor Plans: Time (in hours) required to create first and second floor plans.



Elevations depict the exterior of a building when viewed straight on. This task comprised the creation of the four primary building elevations—north, south, east, and west—as well as additional partial eleva-tions showing the western-most end of the hospi-tal. In order to more accurately show the building, several of these elevations also showed cross-sections through portions of the building.

Elevations in AutoCADSince the AutoCAD building plan existed as only a two-dimensional drawing, lines were projected from the floor plan in order to create the elevations, a technique typically used in manual drafting. After projecting the geometry, each elevation had to be completed manually by first creating blocks to repre-sent the windows and then adding those 2D windows to the elevation. Hatch patterns were also added to indicate the brick walls and concrete spandrel beams. Each time a unique block or hatch pattern was created, it was added to a custom tool palette so that it could be reused by simple drag-and-drop techniques. A considerable amount of time was saved by custom- izing AutoCAD’s tool palette in this way.

Elevations in Autodesk RevitIn Autodesk Revit an elevation is just another way of viewing the building model. Revit generates eleva-tions automatically as you create floor plan views. And since the Revit building component definitions include information about the types of materials used, the resulting elevations automatically depict the proper materials. So there was no need to add hatch patterns to the elevations to represent the brick and concrete. Those materials were properly shown automatically.

Revit also provides specific callout tools for sections, interior/exterior elevations, and details. These callout tools automatically create associated views from the three-dimensional building model. So the only step needed to create the additional partial elevations was to place the necessary callout into the model.

Figure 6. Lines are projected from floor plans in order to create 2D elevations in AutoCAD. Hatch patterns, labels, and callouts must then be added manually.

Elevations

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Task 2 – Elevations

Subtasks CAD BIM

Project geometry from floor plans 0.75 n/a

Create 2D blocks of window elevations 0.5 n/a

Complete elevations 5.5 0.03


Comparing this task in AutoCAD versus RevitAt this stage the productivity advantage of Autodesk Revit became apparent. It took 6.75 hours to create the building elevations using AutoCAD, whereas Revit had already created the four primary elevations

automatically and the additional partial elevations took just minutes to create. These results are detailed in the following table.

Task 2 – Elevations: Time (in hours) required to create the four primary elevations and a partial west elevation.



Reflected ceiling plans show the arrangement of ceiling grids and the locations of light fixtures and other ceiling-mounted components.

Reflected Ceiling Plans in AutoCADThe floor plan drawing was reused to complete this task in AutoCAD. Layers on which elements such as doors and plumbing fixtures, which are not visible in the ceiling plan, sit were frozen, and new layers were created on which the ceiling grid and light fixtures would be created. A user-defined hatch pattern was created to represent the 2x4 ceiling tile pattern needed for the hospital. The perimeter of each room was manually outlined using polylines and then the ceiling pattern added to each room as a hatch pattern. AutoCAD’s grip editing capability made it relatively easy to adjust the position of the ceiling grid pattern in each room.

Once the line work representing the ceiling tiles was in place, a dynamic block was then created to repre-sent the light fixtures. This block was added to the custom tool palette so that light fixtures could be added to the ceiling plan using drag-and-drop.

Reflected Ceiling Plans in RevitIn Autodesk Revit, the ceiling plan is another auto-matically created view. A ceiling tool enables the appropriate ceiling to be added to each room by simply clicking inside the room. Once the ceilings were in place, light fixture components were loaded from Revit’s library of pre-defined families and placed in their proper position within the ceiling grid.

Subtasks CAD BIM

Draw first floor ceiling plan 1.25 0.65

Add light fixtures to first floor ceiling plan 0.5 0.75

Draw second floor ceiling plan 1.0 0.35

Add light fixtures to second floor ceiling plan 0.25 0.25

TOTAL TIME: 3.0 2.0

Comparing this task in AutoCAD versus RevitOnce again, the intelligent nature of Autodesk Revit resulted in significant time savings. This task took three hours to complete in AutoCAD versus only 2 hours in Autodesk Revit, a 50 percent productivity improvement. These results are detailed in the following table.

Reflected Ceiling Plans

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Task 3 – Reflected Ceiling Plans: Time (in hours) required to create the reflected ceiling plans.



Building sections show a view through a building, aiding in understanding the design of a building and are a significant part of construction docu-ments. While several of the elevations created in task 2 showed partial sections through the building, two major cross-section views through the entire building were required: one through the length of the building looking toward the north and one through the width of the building looking toward the west. The later section also extended through the entire single-story wing of the hospital.

Building Sections in AutoCADCreating the building sections in AutoCAD involved methods similar to those used to create the buil-ding elevations. First, lines were projected from the floor plan and used as the basis to manually draw all of the two-dimensional line work representing the building section.

Building Sections in RevitIn Autodesk Revit, building sections are created automatically by simply placing a building section callout into one of the existing views. Sections are just another parametric view of the underlying building model.

Figure 7. Building sections are created automatically in Autodesk Revit by simply placing the appropriate section callout and indicating the direction of the view. If the building model is subsequently modified, the section automatically updates to reflect those changes.

Comparing this task in AutoCAD versus RevitThis task took just minutes to complete using Autodesk Revit versus nearly four hours using AutoCAD, a productivity improvement of 365 percent.

Subtasks CAD BIM

Create building section looking north 1.75 0.05

Create building section looking west 2.0 0.05


Building Sections

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Task 4 – Building Sections: Time (in hours) required to create the building sections.



In both AutoCAD and Autodesk Revit objects are created at full-size. In the case of the hospital, that meant that the plans, elevations, and building section drawings depicted a building more than 250-feet long and 200-feet wide. Similarly, in Revit the building was modeled in 3D at its actual size.

With many of the basic plan, elevation, and building sections complete, the project had progressed to the point that one could begin to create the individual sheets that would comprise the set of construction documents. In order to create the construction doc-uments, however, the drawings or building model must be scaled down and placed onto a computer-ized representation of the sheets of paper comprising the construction documents at a manageable size.

Construction Documents in AutoCADAutoCAD’s sheet set capability is designed specifically for creating a set of documents comprised of multiple drawings. Once the individual sheets were created, complete with a border and titleblock, the individual drawing files could be dragged and dropped onto those sheets, creating paper space viewports. This enables the drawings to be placed onto the appro-priate sheets at an appropriate scale.

Construction Documents in Revit The method of creating construction documents in Autodesk Revit is quite similar. In Revit, a titleblock family determines the sheet size, border, and titleb-lock. Multiple sheets are then quickly created based on this family. Then, the various floor plans, eleva-tions, and section views can be dragged and dropped onto the appropriate sheet.

Figure 8. Because the AutoCAD drawings of the hospital were drawn in 2D, adding a perspective view of the hospital building to the cover sheet required the creation of a simple 3D model of the building mass onto which 2D elevations were then mapped to create the appearance of a 3D model.

Construction Documents

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Task 5 – Construction Documents

Subtasks CAD BIM

Create a sheet set 1.25 n/a

Create cover sheet including perspective view 1.25 0.15

Create sheets and place floor plans and ceiling plans 0.85 0.4

Create sheets for elevations and sections and place those views 1.0 0.2

Create empty sheets for later addition of details and schedules 0.15 0.15

TOTAL TIME: 4.5 0.9

Comparing this task in AutoCAD versus Revit There was one interesting twist to the creation of the construction documents, however. The original hospital drawings included a cover sheet that in turn included a perspective view of the hospital. Since the building was created only in two- dimensions in AutoCAD, in order to include this perspective view, a 3D simple wireframe outline of the building was created in AutoCAD and then the individual 2D elevation views were inserted as blocks onto the simple 3D model as appliqués, thus creating the appearance of a 3D model. This additional process added more than an hour to this task in AutoCAD.

But since the building was actually modeled in 3D in Autodesk Revit, creating a perspective view that could then be added to the cover sheet required little more than using Revit’s camera tool to create a perspective view. That view was then placed onto the cover sheet using drag-and-drop, just like any other view. This additional operation added just a few minutes to this task in Revit.

The completion of this entire task—creating ten sheets to accommodate the various views and placing onto the sheets those views that had already been completed—took 4.5 hours in AutoCAD compared to less than 1 hour in Autodesk Revit, a difference in productivity of 80 percent.

Task 5 – Construction Documents: Time (in hours) required to create the ten sheets of construction documents.



Architectural construction documents often include many sheets consisting of drawings showing specific construction conditions, such as the junction between walls and floors, at larger scales.

Rather than re-create the more than 15 individual sheets of details that comprised the original hand-drawn construction details for the hospital, the study included a single sheet containing five details representative of the types of large scale drawings that would normally be created: an enlarged plan view of a typical two-bed patient room, a large scale cross-section through the primary exit stair tower, section through a typical wall, and large scale details of that wall showing the specific conditions at the floor and ceiling.

Large Scale Details in AutoCADUsing AutoCAD to create the enlarged floor plan of a typical two-bed patient room required little more than to place a view of the first floor plan on to an appropriate sheet in the sheet set, adjust the size and scale so that only the two-bed patient room was visible, and then adjust the layer visibility so that only the necessary information would be visible. But in AutoCAD all of the other details needed to be created from scratch. Once again, this process began by projecting lines from the floor plan. Creating the section through the stair tower was particularly time consuming, since each component had to be created manually in AutoCAD. Similarly, each dimension had to be placed manually. To label components, indi-vidual leaders had to be placed and then each note manually typed. These individual drawings were then added to the sheet within the sheet set.

Large Scale Details in RevitIn Autodesk Revit, creating the enlarged plan of the typical two-bed patient room required simply placing a callout onto the floor plan. Similarly, the section through the stair was created by simply placing a section callout through the stair on the floor plan. The typical wall section was created the same way. In each case, adding the callout caused Revit to auto-matically create the appropriate view. It was then a simple matter to drag-and-drop these views onto the appropriate sheet.

To create the large scale details of the concrete spandrel beam at the floor and ceiling, additional callouts were added to the wall section. Again, this caused Revit to automatically create these enlarged detail views. Additional detailing was quickly added using Revit’s detail component library and draft-ing tools. In addition, Revit’s keynoting capabilities enabled many annotations to be added without any typing, since the software could automatically recognize many of the building components shown in the detail views.

Large Scale Details

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Task 6 – Large Scale Details

Figure 9. In Autodesk Revit, typical wall sections, enlarged plan views, and even details can be created as just another view of the underlying parametric building model, by simply adding an appropriate callout to an existing view. Revit also includes a robust set of drafting functions and an extensive detail library, making it easy to create additional custom.

Comparing this task in AutoCAD versus RevitIt took a fraction of the time to complete this task using Autodesk Revit compared to AutoCAD—one hour compared to 4.5 hours—a productivity improvement of more than 75 percent. And since this task represen-ted just a single sheet of what would normally be many sheets of large scale details, in an actual project, the time savings could be even more significant.

Subtasks CAD BIM

Create enlarged plan view 0.25 0.15

Create section through stair 2.5 0.45

Create typical wall section 0.75 0.15

Create details of concrete spandrel beam at floor and ceiling 0.75 0.25


Task 6 – Large Scale Details: Time (in hours) required to create a single sheet containing five typical large scale details.



Construction documents are about more than just drawings. Schedules are used to enumerate elements of a project that cannot be depicted graphically. For example, a door schedule is a list of all of the doors in the project, with specific information about the door size and type as well as information about the fire rating, hardware, and other data that cannot be represented by the door in its graphic form. Similarly, a room finish schedule is a list of all of the rooms in the project along with specifics about the material applied to the floor, walls, and ceiling of each room.

Because the information conveyed in schedules often changes as the project evolves, it is important to create them in such a way that they can be updated after any changes are made to the plans. For example, if a door size is changed, the resulting schedule needs to update to reflect the change.

Schedules in AutoCADIn order to create a schedule in AutoCAD, attribute data is typically associated with blocks that are inserted into the drawing.

For example, the label added to each room in the floor plans included attributes that stored the data specifying the finishes applied to the floor, walls, and ceiling of each room. That data could then be extracted directly to a table within AutoCAD and the table placed onto a sheet. Similarly, the dynamic blocks representing the doors included attribute data that stored information about the fire rating, material, and hardware associated with each door. The actual dimensions of each door, however, was derived directly from the properties of the dynamic door block itself. So if the size of the size of the door changed, that value also changed automatically.

That said, in AutoCAD, the creation of schedules is a one-way process. In order to reflect a change, the dynamic block or attribute data must be updated in the floor plan and then AutoCAD’s Attribute Extraction wizard must be run a second time, creating a new table to replace the one previously created.

Figure 10. The Attribute Extraction wizard in AutoCAD enables users to extract attribute and dynamic block properties directly to a table, making it quite easy to create schedules based on data stored within the drawings.

Schedules

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Task 7 – Schedules

Schedules in RevitIn Revit, a schedule is simply a text-based view of a building information model. Using Revit’s schedule tool, it was a simple matter to create the door schedule and room finish schedule based on tags that were automatically added when doors and rooms were placed while originally creating the floor plans. Those schedules could then be dragged-and-dropped onto the appropriate sheets.

But in Revit, since schedules are just another type of view, they are bi-directional. Changes made within a schedule affect the other views. For example,

changing the size of a door within the door schedule causes that door to update in the floor plan and all other views as well. Revit also enables the creation of key schedules. For example, the hospital has many patient rooms and the finishes of each patient room are the same.

Rather than having to define the finishes separately for each patient room, a room type category can be defined within the context of a key schedule. All patient rooms can then quickly be assigned the same finish by simply applying that room type key to each patient room.

Subtasks CAD BIM

Create door schedule 0.75 0.25

Create room finish schedule 0.25 0.25

TOTAL TIME: 1.0 0.5

Comparing this task in AutoCAD versus RevitAlthough the ability to extract dynamic block properties and attribute data to automatically create a table in AutoCAD is a tremendous time saver compared to other methods of creating schedules that had been used in the past, it still paled in comparison to the tools in Revit. It took an hour to complete this task in AutoCAD compared to just 30 minutes in Revit, a 100 percent productivity improvement.

Task 7 – Schedules: Time (in hours) required to create the door and room finish schedules.



In the real world of building design, changes are unavoidable. In the case of the actual hospital project, in 1979, as work on the original construction docu-ments neared completion, the design team discov-ered that the location of one of the existing buildings to which the new addition would connect had been recorded incorrectly and the drawings created there-fore included that error. Although the discrepancy was less than 18 inches, the error resulted in exten-sive rework to portions of the plan, and all of that rework had to be done by hand with a pencil and eraser.

Had the original hospital project been done using any CAD system, much of the time needed to erase and redraw line work could have been avoided by simply moving objects that had already been drawn.

To reflect the types of changes that often occur in typical architectural projects, this task was included to provide a series of both minor and major edits, to see how CAD and BIM handled change. These tasks involved moving doors and walls as well as changing several rooms from four-bed to two-bed patient rooms. These modifications resulted in changes that would need to be reflected in both the first and second floor plans and reflected ceiling plans, the building elevations and sections, and in the door and room finish schedules.

Project Modifications in AutoCADSince AutoCAD objects contain no intelligence, even a small change, such as moving the location of a door or changing the size of a window, required a considerable amount of manual rework. For instance, moving a wall a few feet required adjoining lines to be redrawn. And when a block representing a door was removed from one section of a wall and added to another, the original opening had to be healed to close the original location of the door and then a new opening created in order to place the door at its new location.

Each reflected ceiling plan also had to be manually edited to reflect the changes required to correct the building alignment error. In AutoCAD, changes that affected the building elevations and sections were even more problematic. Since the elevations and sections were each created manually using simple line work, each change required manual rework of these drawings as well. After all of the changes were made, the door and room finish schedules also had to be replaced with new tables generated by re-running the Attribute Extraction wizard. Lastly, because several of the patient room types changed, and these changes were reflected in the size and spacing of windows visible in the perspective view that had been placed on the cover sheet, the perspective view in AutoCAD also had to be manually updated.

Project Modifications

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Task 8 – Project Modifications

Figure 12. Since Revit models actual building objects, when the user moves a door, the opening automatically heals itself at the old location and creates a new opening at the new door location.

Project Modifications in RevitIn Autodesk Revit, objects maintain their relation-ships and design changes propagate through the entire building model. For example, when a door was removed from one location and placed in a new loc-ation, the old opening automatically healed itself and simply placing the door at its new location caused a new opening to be created automatically.

Similarly, since the reflected ceiling plans, elevations, and building sections are all simply different views of the same building information model, a change made in any view is immediately and automatically reflected in all other views. In fact, changes can be made in whichever view is most convenient. For example, if a window is moved in a plan view, the change imme-diately appears in the elevation view as well. But the window could also be moved in the elevation view and that change immediately reflected in the plan

view as well. As a result, any information that gets changed anywhere is effectively changed everywhere throughout the model. This capability even extends to schedules. When a patient room was changed from a four-bed room to a two-bed room, the room name could be easily changed in the schedule and that change immediately was reflected in the floor plan view.

Comparing this task in AutoCAD versus RevitThis task provided one of the most dramatic illustrations of the benefits of using Autodesk Revit to model the building in three-dimensions rather than using AutoCAD to draw the various views of the building in 2D. While the more than 2 hours it required to make the changes in AutoCAD was much faster than the several days it required to modify the original hand-drafted hospital drawings back in 1979, it was still 80 percent slower than the 30 minutes it required to make the same changes using Autodesk Revit.

Subtasks CAD BIM

Modify floor plans 1.0 0.3

Modify reflected ceiling plans 0.5 0.2

Modify building elevations 0.15 n/a

Modify building sections 0.1 n/a

Modify schedules 0.1 n/a

Update perspective view 0.5 n/a


Task 8 – Project Modifications: Time (in hours) required to make the modifications required to update the drawings after discovering the building alignment error.



Project coordination is often a very time consuming process. Architects must make sure that the draw-ings are complete, that all callouts correctly refer to the proper drawings on the correct sheets, and that all the necessary information is provided. Then, the drawings must be sent out for reproduction. If a detail, a sheet, or even an important notation is inadvertently omitted, the project can be delayed.

In the productivity study, this task involved reviewing the sheets, making minor modifications to several of the drawings, adding additional callouts for various elevations, sections, and detail views, and linking them to the appropriate views on individual sheets.

Coordination and Publishing in AutoCADIn AutoCAD, this task was aided by sheet set tools that enable all of the sheets to be published in a sin-gle step. Those sheets could be printed or published

as industry-standard PDF files, or as DWFTM (Design Web Format) files. DWF is a format developed by Autodesk as a medium for architects, engineers, and other design professionals to help them quickly capture and more securely distribute rich design data anywhere it is needed. Anyone can view and print DWF files using free* viewing tools provided by Autodesk.

* Free Autodesk software licenses and/or cloud-based services are subject to acceptance of and compliance with the terms and conditions of the license agreement or terms of service, as applicable, that accompany such software or cloud-based services.

Coordination and Publishing in RevitSimilar tools in Autodesk Revit also enable all of the sheets to be printed or published in a single step. Again, those sheets could be published as a DWF file, but Revit does not include the ability to publish directly to PDF. However, if a PDF printer is already installed, Revit can print to a PDF file.

Comparing this task in AutoCAD versus RevitWhile both programs include tools that make it easier to coordinate and publish sets of construction documents, Revit again held a distinct edge because its tools are purpose-built for construction documents whereas those in AutoCAD are more general in nature and therefore need to be customized to reflect stand-ard architectural practices. It took more than an hour to add callouts, make other corrections, and publish the ten sheets of drawings using AutoCAD, whereas it took just 12 minutes to accomplish the same task in Revit, a productivity improvement of 525 percent.

Subtasks CAD BIM

Add callouts and make other corrections and additions to the drawings 1.0 .01

Publish the construction document set 0.25 .01


Coordination and Publishing

9

Task 9 – Coordination and Publishing: Time (in hours) required to coordinate and publish the set construction documents.



The final task in the productivity study required the creation of two near photo-realistic renderings, one of the exterior of the hospital and one of the interior of a typical two-bed patient room. While renderings of the proposed hospital addition were created by an architectural rendering service when the project was commissioned in 1979, the rendering capabilities in both AutoCAD and Autodesk Revit make it feasible for anyone to produce high-resolution photo-realistic renderings.

Creating the Renderings in AutoCADSince all of the drawings of the hospital with the exception of the perspective view on the cover sheet where created in AutoCAD as two-dimensional draw-ings (and the way in which that perspective view was created did not enable it to be used as the basis for producing a rendering), a three-dimensional model of the hospital had to first be created in AutoCAD before a rendering could be produced.

Rather than model the entire building in 3D in AutoCAD, however, only the portions of the building that would appear in the resulting renderings were created. For the exterior rendering, portions of the exterior walls were modeled in 3D by first starting with the two-dimensional floor plan view, drawing closed polylines, and then extruding those polylines as solids. Similar methods were used to model the concrete spandrel beams and windows. The louvers below the windows were created by sketching the two-dimensional louver profile and then sweeping that profile along a linear path. Since most of the windows are identical, once one window was mod-

eled in 3D, it was relatively easy to copy that one instance to create the remaining windows. Materials were then added from AutoCAD’s extensive material library and applied to the various building compo-nents to represent realistic brick, concrete, glass, and other building components. AutoCAD’s geographic location tools were then used to so that the building could be more realistically lit by simulated sunlight. Fi-nally, a view was created by using AutoCAD’s camera tool to place a camera into the model. The properties of that view were then adjusted so to represent how the building would look when photographed using a 30mm lens. The resulting rendering, produced at Presentation quality at a resolution of 2048x1536, was a fairly accurate representation of the hospital, but had a different viewpoint been required, addi-tional modeling would have been needed.

Similar methods were used to create the rendering of the interior of a typical patient room. Three- dimensional geometry representing the walls was first created by drawing closed polylines over a portion of the floor plan. Those polylines were extruded to create solids. Other solids were created and subtrac-ted from the walls to create openings for the doors and windows. Then other solids were modeled to represent the doors and windows that filled those openings. Solids also had to be created to represent the floor and ceiling.

Again, materials were located in AutoCAD’s material library and applied to the floors, walls, doors, windows, and so on.

Renderings

10



Task 10 – Renderings

Creating the Renderings in RevitCreating the two renderings in Revit proved to be quite simple. Since the entire hospital was already modeled in 3D, creating the exterior and interior views involved nothing more than using Revit’s cam-era tool to place a camera at the desired locations outside the building and inside of a typical patient

room. There was no need to apply materials since the proper materials were already part of the definition of the various components comprising the building model. The exterior rendering was produced at the program’s High render quality, at a resolution of 2012x1080 pixels.

Figure 13. Before renderings could be created in AutoCAD, portions of the hospital had to be modeled in 3D. Although the interior rendering of the typical patient room is a fair approximation, the ceiling grid pat-tern is not accurate and the light fixtures were created by cutting holes in the solid representing the ceiling.

While the material applied to the ceiling accurately represented the 2x4 ceiling tiles, there was little way to control the position and alignment of the rendered ceiling grid. In addition, openings were created in the ceiling to represent the light fixtures and then AutoCAD light objects were added in order to illuminate the interior of the room. As a result, the rendering, again produced at Presentation quality at a resolution of 2048x1536, was a close approxima-tion of the actual room interior, but was not totally accurate. Had models of the light fixtures been made, the results might have proven more realistic, but ad-ditional modeling time would have been required.

Figure 14. The exterior rendering created in Revit was created by simply placing a camera at the desired location. Since the building and the surrounding terrain was already modeled in 3D, there was nothing else required in Revit other than to wait for the rendering to be completed.



Task 10 – Renderings

Figure 15. The interior rendering created in Revit also required no additional work other than to place a camera at the desired location inside the building model. The resulting rendering yielded a more realistic result than AutoCAD, with the ceiling tiles better positioned and light emanating from the ceiling mounted light fixtures.

Comparing this task in AutoCAD versus RevitThis task proved to be no contest. It took more than 2 hours to model enough of the building in 3D in AutoCAD in order to then create the two renderings, while in Revit, the 3D model already existed. Although AutoCAD was able to generate the resulting renderings on the local computer faster than Revit—6 minutes: 5 seconds versus 20 minutes: 47 seconds—those renderings were not as accurate or of as high a quality as those produced using Revit. It took more than 2 hours to complete this task using AutoCAD versus less than 1 hour using Revit, with all of the Revit time consisting of waiting for the computer to finish computing the rendering.

Subtasks CAD BIM

Model the exterior of the building prior to rendering 1.25 n/a

Render the exterior view at High or Presentation quality 0.04 0.06

Model the interior of the building prior to rendering 0.75 n/a

Render the interior view at High or Presentation quality 0.06 0.28


Similarly, there was no need to add lights to illumi-nate the interior of the patient room since the lights that had already been placed in the reflected ceiling plan represented real light fixtures. In the rendering, those light fixtures illuminate the interior of the room similar to as they would in the real world and the ceiling tiles are positioned more accurately in the resulting rendering. The interior rendering was produced in Revit at the program’s High render quality, at a resolution of 1669x1081.

Task 10 – Rendering: Time (in hours) required to complete an exterior and interior rendering.



It took more than 48 percent longer to create the identical set of construction documents and complete two renderings with AutoCAD software than with Autodesk Revit, which represents a productivity difference of more than 91 percent.

Productivity Comparison of AutoCAD 2015 and Autodesk Revit 2015: Time required to complete the entire project.

BIM CAD

TOTAL TIME: 26 h 22 min 50 h 27 min

In this task, the purpose-built tools for Building Infor-mation Modeling in Autodesk Revit enable a level of efficiency and productivity for architects, engineers, and other building design professionals that is better than the more general purpose CAD tools in AutoCAD. • Because it is a discipline-specific building modeling

and documentation system, the tools in Revit may be familiar.

• The parametric change engine automatically coordinates changes made anywhere within the building information model, helping to keep construction documentation up to date.

• Autodesk Revit can produce AutoCAD DWG files as final deliverables and can import existing AutoCAD drawings for use within Revit.

There are other aspects of Building Information Modeling that not considered within the scope of this study that help further enhance an architect or engi-neer’s productivity when modeling in Revit, such as:

• the ability to distribute and share work on a Revit project across a multi-discipline design team,

• to more quickly iterate and investigate multiple design options,

• to more easily handle project phasing, • to employ conduct analysis to better understand

the performance of various building systems. And since the entire Revit building information model is saved within a single Revit project file, file manage-ment issues are minimized compared to producing a project of this scope using AutoCAD.

Autodesk Revit is a smarter, more productive environment for all phases of design and construction documentation. From conceptual studies through the most detailed construction drawings and schedules, Revit provides a competitive advantage, delivers better coordination and higher-quality drawings and renderings, and can contribute to higher profitabil-ity for architects and the entire building design and construction team.

Conclusions


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