AEC Tech News #142
20 Apr, 2005 By: Michael DakanMore About Text Height
Cadalyst Newsline readers debate which size should be standard for construction drawingsCadalyst'sNewsline weekly e-mail newsletter recently played host to a debate about the proper height for text in CAD drawings for construction. A Newsline reader requested feedback on the topic, and a few dozen others replied. (Those responses are posted on Cadalyst's AEC Web site.)
A strong consensus emerged that supported a standard text height of 3/32" for use in general notes and annotation. I can concur with 3/32" as a very workable and readable height for most purposes, and although I doubt if I can add much to the thoughtful discussion and ideas expressed by the many respondents, I would like to summarize the discussion for the benefit of my AEC Tech News readers.
All discussions presumed some kind of printed output as the final deliverable. That is still the norm in today's AEC world and will undoubtedly be the case for the foreseeable future. As much as we might like to think that 3D modeling and BIM (building information modeling) electronic files will change this situation soon, those ideas have not yet gained common use in AEC.
Output Devices
Respondents generally didn't discuss which output devices they are using, but of course this can make a tremendous difference in plot quality, especially if the plotter doesn't have sufficiently high resolution for the required tasks. You need at least 600dpi resolution, especially if you are producing half-size scaled plots or smaller. Most contemporary output devices such as inkjet plotters and laser printers are capable of 600dpi. A few respondents complained about reduced-scale drawings containing indistinct lines and muddy text, so perhaps some people are using inadequate, lower-resolution plot devices.
Respondents discussed producing reduced-scale drawings for various purposes, and of course this affects text readability. Most everyone agreed that 3/32" text maintains good legibility when plotted at half-size and even smaller. A few respondents talked about reducing E-size drawings (30" x 42") to 8 1/2" x 11" and thought that 3/32" text was pretty small and maybe not very readable at that level of reduction — which I think should be expected. If you are commonly producing reductions such as full floor plan drawings reduced to 8 1/2" x 11", you probably need to standardize on 1/8" full-size text height, perhaps even 5/32".
Faxing
A couple of respondents talked about producing 8 1/2" x 11" drawings for the purpose of faxing. Faxing presents an especially difficult problem for drawing legibility. A standard office fax machine typically transmits and receives at 150dpi resolution at best, so it's very difficult to maintain good legibility. Instead, I would suggest e-mailing an Adobe Acrobat PDF file plot output. (For more information about digital publishing, read the feature on 2D CAD publishing, coming in the May issue of Cadalyst magazine.)
Line-Weight Scaling
Surprisingly, no one mentioned line-weight scaling for reduced output. I think it is essential to use this feature for producing reduced-scale output drawings, so line weights are reduced according to the reduction factor of the drawing output. In AutoCAD, for example, line-weight scaling can be enabled through the Page Setup Manager dialog box, in the Plot Scale area. A toggle check box enables this feature, but is only available when plotting from a Page Setup, not from model space. Several Newsline respondents who complained of heavy lines and blocky text in reduced-scale drawings obviously aren't using this feature, or perhaps are using CAD software that doesn't offer it.
National CAD Standards
Also surprisingly, only a couple of respondents mentioned the U.S. National CAD Standard as a resource for information regarding recommended text height. Or maybe this shouldn't be surprising, given the perceived irrelevance of NCS to most CAD users. The NCS should be the definitive source for such information if it were functioning as a real national standard for AEC — but it obviously isn't.
I discussed NCS in detail in the February 3 and February 17 editions of AEC Tech News. The U.S. National CAD Standard Web site is at http://www.nationalcadstandard.org.
Summing Up
Text height remains one of those subjective, debatable areas that is a topic of much wasted time and energy and ultimately leaves everyone to determine their own approaches. Much of what each user decides depends on how CAD drawings are used, the standard font used for annotation, whether or not reduced full-size output is commonly needed and so on. In this context, perhaps there is no definitive standard to go by, but rather only a consensus regarding what seems to work adequately for most users.
The important thing to keep in mind is the ultimate goal of clean, legible drawings that clearly and unambiguously convey design intent. Using 3/32" text height seems to be a good standard height for starters. Then adjust as needed to suit your specific needs and end uses.
