A question on construction drawings: Dimensioning
I wanted to put this question out to the group re: construction documents / plans that you often times have to work from that are provided by an outside designer or architect. I’m a former general contractor / builder who used to do designing as well as building. I am now getting back into the business but as of now only as a designer. The question I had is about dimensioning, and what do you find that works best for you.
When I was a builder and I had to work from plans from an outside source for new construction work, I always liked to have the dimensions on the drawings be ‘face of stud’ (F.O.S.). I’m wondering if others here feel the same way. I liked F.O.S. for new construction and any part of a remodel where there was essentially new work. (By this I mean a remodel where there was an obvious area where there was new construction such as an addition). Obviously F.O.S. doesn’t really make sense for existing buildings…usually. But, the reason why I always found F.O.S. more straightforward and ‘builder friendly’ is that it made it easier for laying out framing. There was no need to have to subtract or add finishes, etc. etc. The arithmetic was straightforward, and it showed that the designer or architect had already figured out any clearance issues with regards to finished surfaces beforehand. In other words, unless the designer was totally incompetent, it was already ‘baked in the cake’ so to speak. So, just wondering if anyone here had any strong opinions either way with regards to how drawings are dimensioned. Thanks for any feedback. -jonR
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Most plans I work off of make the framer (usually me) determine how to layout out walls in the field. Example, we know by code that hallways have to be 36” min wide by code. Plans most often show 36” wide dimension for hallway with 4” walls (not 4 1/2”, 4 3/4” and so on). If the framer snaps lines at 36” w/ drywall you will be 1” smaller than what code allows. I believe most of the software have default settings of 4”, so that’s probably the reason architects often indicate a 4” wall. For me designing to finish vs frame is better. A lot of my work can get complicated at times. Often my walls have different fire ratings from one another, so require multiple layers of drywall vs one. Also, finishes can get a bit complex at times, so have to take into account all the allowances for that, better done in the field by the people actually doing the building. If you are designing simple production type housing with minimal finishes and assumed 1/2” drywall on all surfaces I can see F.O.S. dimensioning being beneficial as the framers used for those projects tend to not have as much knowledge of code concerns and finish procedures. On custom homes and commercial projects things are a bit more complicated.
Thanks for the feedback. First off, the software (various CAD programs) does not default to 4". That imprecision is the result of architects, designers not really caring. I've asked a few about that and you usually get some sort of vague answer or shoulder shrugs, like it's not big deal. I think you misunderstood some of my questions, which is completely reasonable since they could be taken a few different ways. First off, I'm defining the process, of 'laying out walls' as just the stuff that a builder does in the field with regards to making cut lists and marking up plates, etc. etc. I was not defining that as figuring out tolerances such as stair width clearance and clearance around toilets, etc. and all sorts of other code compliance situations. And adding in the thickness of finishes. I was putting that in the realm of what the *designer* should be doing. So, if a designer produces drawings that are dimensioned FOS, all the figuring about finished surfaces should be 'baked into the cake'...by the designer. And if that's done properly, drawing stud walls with the correct width and dimensioning them FOS should still meet code compliance, if the builder follows the FOS plans verbatim. So, for example, if you are handed a drawing that is dimensioned FOS, and the stairway width is 37" and the wall finish is 1/2 drywall, then the designer has done their job assuming you were shooting for 36". So, I guess the way I laid this out (no pun intended), it sort of leads to FOS as a preferred method. I guess I was wondering how valuable that would be to a builder...other builders besides me. I found that valuable and consistent....was wondering if I'm making too big a deal of this or whether others had the same attitude.
It would be very much appreciated to provide FOS measurements and an experienced person like you I could trust for factoring allowances etc. Unfortunately most (not all) designers I’ve worked with do not understand how to build something, so I’ve been forced to figure it out on my own as I know they do not factor these things. That’s interesting that 4”, 6”, 8” walls are not default settings for software. I assumed they were as my software’s default setting is 4”, but I use very basic software as I only design for my work.
I'm with you. Face of stud to face of stud. Or maybe even say face of framing to face of framing. If you are in the business, you should know the code about critical finish dimensions such as hallways etc. and dimension accordingly.
Also, I don't like center to center dimensions. Even when showing the roof framing layout. It's easier for me to do the calculations with my calculator than for the framer to do it on the job. That's my two cents. FWIW
I hate it when designer/arch. considers wall etc. to be 2",4",6" etc. It only works for them. Not the framers. A dimension should not be a + or - thing but exact.
Thanks for your input. Yeah, it sorta drives me crazy when a 2x6 stud wall (just the framing) is shown as 6"...same with 2x4 walls. Btw, I have no problem with 'center to center' because it is still compatible functionally and conceptually with a FOS approach to dimensioning. And sometimes when the drawings are developed, the exact window rough opening is not known. So, when that R.O. info is known, (hopefully before framing starts :-) ), the dimensioning will still be relevant. Here's another method that I've seen involving FOS, and it is sort of elegant in that it shows attention to detail. You draw the walls at full thickness, (framing with all finish materials), BUT you still dimension FOS. So....when doing this, the extension lines of your dimensions will hit the wall accordingly. In other words, for 1/2" drywall, the extension line will be 'in' 1/2" from the end of wall/corner, etc. What it communicates is this: The dimensions are FOS, but the walls are drawn with an accurate width as per the specifications. I know that programs such as Revit have the settings that will allow you to do this.