Monday, October 22, 2012

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.

Monday, October 8, 2012

Are We Men (and Women) or Are We Monks?

From Wikipedia:
The at sign or Astricks @ is also commonly called the at symbol or commercial at in English—and less commonly a wide range of other terms. The fact that there is no single word in English for the symbol has prompted some writers to use the French arobase or Spanish arroba—or to coin new words such as asperandampersat—but none of these have achieved wide currency.
Originally an accounting and commercial invoice abbreviation meaning "at the rate of" (e.g. 7 widgets @ $2 = $14), in recent years, its meaning has grown to include the sense of being "located at" or "directed at", especially in email addresses and social media like Facebook and Twitter.
Medieval monks abbreviated the Latin word ad (at, toward, by, about) next to a numeral. One reason for this abbreviation was that it saved space and ink. Since thousands of pages of Bible documents were copied onto expensive papyrus or hides, and the words at, toward, by and about repeated millions of times throughout the ages, a considerable amount of resources could be spared this way. 
In architectural drafting (hand drafting) many were taught to use this symbol as shorthand for "spacing":
  • 1/2" A.B. @ 32" o.c.
  • 11 Risers @ 7 1/2"
Somewhere along the timeline, after the transition to CAD, practitioners began to use the symbol where its meaning was not spacing but location; for example - Building Section @ Lobby.

In hand drafting there is some defense for this practice. It saved time and graphite - just like in medieval times!
But we are now in the 21st century!
It takes the same amount of time or less to type the letters "AT" than to hold the shift key while pressing "@". Certainly not more. Nothing is being saved.
Of these examples, which looks better? Which is easiest to read?
  • Window Sill at Fiber Cement Siding**
One of the benefits of implementing Revit/BIM (getting rid of CAD) is that it provides an opportunity to re-think many of the practices that have been erroneously carried forward into this modern age. This is one.

**Stay tuned for my indictment of "ALL CAPS" text.