Reality & Illusion

In the West (and I assume throughout the U.S. and elsewhere), where wood frame construction is dominant, these standards apply:

Standard length for 9 foot (nominal) studs is 104 5/8" or 8'-8 5/8". With top and bottom plates added, the standard plate height should be 109 1/8" or 9'-1 1/8". This allows for approximately a 9 foot clear interior ceiling height, depending on the finish.

For engineered joists, the actual size of the TJI-12 is 11 7/8", while the TJI-14 is actually 14".

Using these values, the top of 3/4" plywood sheeting will be 10'-1 3/4" for the TJI-12 system; and 10'-3 7/8" for the TJI-14 system. Roof plate heights for the two systems and 19'-2 7/8" and 19'-5" respectively.

In CAD, where accuracy is often pushed aside for expediency (because it's so inefficient?) these values have been "leveled off" to 9'-1", 10'-2", and 19'-3".

Also in CAD, reference values from finish floor are rarely given. The plate to sub-floor dimension is also excluded. The logic (?) being that at the start of the job, the floor assembly depth is unknown, and CAD must be protected from the demand for changes, where it is extremely inefficient.

When modeling with Revit, the best practice is to use actual values whenever they are known. There are no "unknowns" in a Revit model. The model is a record of all the information gathered about the building being designed. What better place to record those decisions accurately than in a Building Information Model?

Practitioners who wish to see no "differences" between CAD and Revit may set the dimension tolerance "to the nearest inch" and exclude the values from the level annotations.

There is no substitute for accuracy. 
When using Revit, do not attempt to substitute an illusion for reality.

Revit Work-Sharing File Protocol

Recently I attended a user group meeting that included a presentation on Revit Work Sharing and Worksets. Eventually three different users spoke about their procedures regarding central and local files, and all of them were different from mine.

Revit Worksharing was introduced in version 4 (2002?) and represented the first true multi-user BIM environment. With this innovation, all objects in the model were assigned to a collection; the "workset", which was required to be checked out by a single user. Conflicts still arose when an objects in different Worksets interacted with each other. These limitations eventually led to the development in version 6 (2004) of "element level borrowing", which lessened the need for Worksets, except on larger projects.

When Worksharing is activated, the single user file is automatically converted to a central file. Copies of the new central file are automatically designated as "local' files which must be periodically synchronized with the Central.

When this feature was initially implemented, all file management was manual. It was not unusual for inexperienced users to accidentally open the central file; one solution was to include the word 'central' in the file name, as a reminder.

Another common problem was the failure to save local changes back to the main file, locking other users out. This led to the so-called "best practice" of creating a new local file every day or even with each new work session. These protocols were originally all manual, and some users created external programs to automate the process.

Starting with version 2010 enhancements were added to make central and local file management more transparent. The Recent Files start-up window and the Recent Documents panel make it easy for users to select the correct file.



Now when users browse to a central file in Revit, the default result is automatic creation of a new local, in the location specified in Revit options dialog. The Revit user name is automatically appended to the central file name, which identifies it as a local file.

Some CAD users have developed the habit of browsing to a file and "double-clicking" it in Windows Explorer (which is fine for single user files). When users open a Revit central file by this method, or any other, they will soon receive a warning to save their work into a new local file.

As with CAD, when using Revit there is no reason maintain some strange attachment to procedures that have become obsolete. The Zen of Revit means developing a sense of "what Revit wants" and following it.

“Core Only” Walls in Revit

Before the advent of CAD, on construction drawings walls were represented by two lines - which everyone understood to represent the wall’s entire thickness. The actual wall assembly was defined by details. The construction layers and finish materials of walls were always shown in larger scale views.

Then as now the standard for dimensions was to reference the face or edge or the core construction, because it must be placed first in the field.  General notes disclaimed “All dimensions are to face of structure unless noted otherwise”. When more specific direction was required, the letters ‘FOS’ or ‘FOW’ were placed next to the dimension line to denote the reference.

At one-eighth inch scale the size of a six inch wall is 1/16”, which is about as fine as can be drafted with pencil on vellum. In manual drafting, at smaller scales the same wall would be drawn thicker, by necessity. The level of detail was variable, depending on the scale of the drawing.

With CAD came the ability to add more detail and precision to drawings. Unfortunately, CAD did not have the human ability to automatically adapt drawing detail level to drawing scale, and management of this information by drawing layers (over hundreds of individual files) although possible, was eventually abandoned because it was impossible to maintain.

So it was all or nothing, and the practice of representing only the structural core of walls, and excluding finishes, evolved into the defacto standard for CAD.

The transition from manual production to CAD did not really resolve its problems; it simply exchanged old limitations for new ones. This compromise is one example of how the limitations of CAD were first accepted and are still perceived as obstacles to overcome in the transition from CAD to BIM.


Among the unintended side effects of this practice, with CAD room and building areas are often calculated by tracing a polyline around the perimeter of a space, not at its finish but at the wall core. Cabinetry and casework is often depicted as if the wall finish does not exist. These errors are not significant, but should hardly be defended when a better solution is presented.

Those familiar with its early history know that Revit was designed specifically to resolve the problems inherent in CAD. Revit allows dimensions to be referenced to structural elements, while also displaying the full thickness of the wall, finish to finish. Revit  also allows walls to be depicted with only two lines (coarse view) with unlimited options for color, fill pattern, and lines weight.

In Revit room areas are automatically calculated, with boundaries established at the user's preference. 

In addition, Revit area plans automatically apply rule-based algorithms for its calculations.


My advice to Revit users is to resist all temptation to use Revit to emulate the limitations found in CAD. Allow what is clearly obsolete to stay in the past where in belongs.

What About Revit?

Note:
In preparing material for this blog I rediscovered this 'manifesto' from the recent past...
(Scroll to the end for the date).

Building Information Modeling for TCF

Architects have relied upon drawings to mediate design and construction since the earliest organized buildings. The abstract language of plan, section, elevation and detail has evolved into a consistent, global standard for conveying design intent to engineers, builders, and owners. So why change now?

However comfortable they may be, the current processes are beginning to prove inadequate in the face of the increasing complexity of projects. Although architects, designers, and consultants have been using computer aided methods for nearly twenty years, the building construction industry still has not realized the productivity benefits experienced by other enterprises that have adopted automated design and production. A recent study by the National Institute of Standards and Technology reported that the lack of integration among the various components of the construction industry costs the United States capital facility industry $15.8 billion per year.   

Revit is more than a modeling program; it is a parametric building information modeling system, the next generation of CAD software. This new tool serves the entire process from design and documentation through procurement, construction and building operation and maintenance. The parametric building modeling technology upon which Revit is built eliminates the most common sources of errors by maintaining a fully-coordinated representation of the building at all times, while accessing that information through the language of plan, section and elevation. 

Revit was designed to overcome the shortcomings inherent in the standard two-dimensional CAD construction project documentation process. In the Autodesk Revit building model, every drawing sheet, every 2D and 3D view, and every schedule is a direct presentation of information from the same underlying building database.





Some of the benefits of this system include: 

• Three-dimensional building modeling for design visualization, rendering and walk-through animation. Models may be exported to other programs for high-end, photo-realistic, imaging. 
• Plan, section, and elevation drawings are automatically generated from the building information model. In Revit, it is impossible for the various drawings in a construction document set to not be in agreement. 
• Changed information is instantaneously and automatically updated throughout the building model and construction documents. 
• Annotations, dimensions, and text use True-type, not vector, fonts, and are automatically re-sized if the scale of a drawing is changed. 
• The location of sections, elevations, and details is automatically referenced and automatically updated when drawing and sheet numbers change. 
• Door, window, and finish schedules are automatically generated from model data. Changes made in schedules are reflected in the construction drawings. 
• Revit is extremely accurate. Building components are defined by their actual dimensions. Construction of a building model in Revit allows the resolution of conditions and conflicts which otherwise would not be discovered until they are encountered during construction. 
• Model data may be exported through ODBC for use with cost-estimating and construction management programs. 

Our Conclusions

The impact of modern technology has finally reached the building construction industry. With better planning, construction predictability will increase while cost and cycle time will decrease. Companies that perform additional planning will benefit from additional fees and reduced risk. Ultimately, the economic beneficiary of better planning is the building owner.

As building owners demand more efficiency and better integration of information, AEC businesses must adapt or find themselves facing obsolescence.

With each successive project for TCF, we expect to add more capability to our building information models, and more value to the services we provide to our client.

A. Jay Holland
Little Diversified Architectural Consulting

January 9, 2006

We've Always Done It This Way!

AutoCAD Version 1.0 was released in 1982. It was one of several desktop 'CADD' applications to evolve from the earlier mainframe and minicomputer CAD systems. See Marian Bozdoc's detailed history of CAD.

In the days of the IBM PC-AT, it was a very common practice to purchase a single copy of the software, to be installed on several computers. AutoCAD became the "defacto standard" by virtue of its availability.
  
Now it's thirty years later and we're approaching the time when the majority of CAD practitioners have never put together a set of documents "by hand". We've always done it this way!

That's not a bad thing. It simply shows how much progress has been made. Over time, the 'best practices' for using CAD evolved into an industry standard and were proliferated throughout the profession.

Many current CAD practitioners may not be aware of how and why these methods evolved, which knowledge is essential when evaluating the need for change. I intend to bring these situations to Light here.

So far I am categorizing these anecdotes as "Strange But True".