Construction documentation and overall detailing tolerances

[x1v1x]

Hello,
I wanted to get some opinions on what people are doing for best practices in regards to CD's and dimensioning details and Revit architecture 2010.

Just as a 2x4 is not really 2"x4" there are dimension tolerances that get screwy. Can anyone tell me what they do and what level of detail they show in their CD package?

Now that we are entering into the CD phase of the job we are starting to lock in dimensions. The questions is that while doing external dimensions you don’t want to show the fine tolerance on the dimensions such as an external wall being 7-5/8” it would come across as 8”. where does that 3/8" go? What is the standard way of addressing these issues In the drawings and where do the dimensions get added and how do we control what is being shown.

Thanks in advance.

[Mike Sealander]

There are a lot of answers depending on your intention. People doing CNC work have tolerances in the thousandths of the inch. I like to build to within a 1/16". However, my wall thicknesses are always the accurate wall thickness of the assembly, so that if a material has a stated industry thickness of 7/16" inch, I don't round that number up or down. Likewise with 3/32" materials, I would accept a dimension with 1/32" precision. There are time when this may seem silly, like when two walls are to be separated by a 20-foot gap. We all know that most of the time dimensioning a 20-foot clear dimension to the 1/32" seems weird. However, I would accept that strangeness over intentionally losing accuracy for the sake of producing a round number dimension.

[patricks]

We model with real dimension thicknesses of building materials, and dimension to the face of core (stud or block) for exterior walls, to the centerline of interior stud walls, and to one side of interior block walls. This almost always eliminates all fractions on my floor plans, while still maintaining true thicknesses of elements.

One of the few exceptions is when an interior wall needs to align to the interior side of an exterior wall, such as with a corridor going to an recessed exterior exit door. Then there will usually be some fractional dimensions. But for us the exterior wall core face location usually takes preference (no fractional dimensions) and the interior wall falls wherever it falls to align with the inside face of that exterior wall.

[cliff collins]

An important best practice for Revit ( or any cad program, as well ) :

Set units tolerance to 1/256" at the onset of the project, BEFORE modeling anything.

Then place model components to even increments of feet, inches, and 1/8" fractions.

Now, when the Structural engineer gets the Arch. model and links it, and places his dimensions, with his tolerance also at 1/256", you will not get the imfamous
12' - 7 29/128" odd fractions showing up everywhere.

Lessons learned long ago, the hard way!

cheers......

[Paul Monsef]

Lessons learned long ago, the hard way!
cheers......
I remember my first drafting job in '97; it was a small SF residence. I received a call one day from the concrete contractor; asking me why my internal dimension strings were +/- 2" more than my overall dimension.

Sloppy drafting? Maybe. But I remembered that when I started working on 200'+ wide buildings four years later.