Dimensions not adding up

[Anonymous]

I run into this from time to time. I've also run into it in other CADD/BIM software. Anyone know what can cause this?

[Brad Elliott]

I'll be a little contrary. I set the accuracy to 1/32 working unit and dimension rounding to 1/8. Between working in angles and making revisions I find trying to keep all accuracies to 1/64 a time consuming folly. I also find 1/64 too hard to rationalize in my head. What does 37/64 round to?

The model is not the product, the building is so I want an accurately dimensioned building as efficiently as possible. I also try to work in 1" intervals so if I see fractions appearing I know to check them. I am also a believer in the time honored tradition of breaking the chain at the least relevant location.

[Da3dalus]

Just to add to the cacophony... I'm in the school that says my job is to create instructions for the contractor to use in constructing the building that I've designed. The model is not the building. I always have a very tight budget to complete these drawings. Therefore, rounding, "+/-" and nudging are necessary to create a clean, readable set of instructions in a reasonable amount of time.

Virtually no contractor is capable of comprehending anything smaller than 1/8", and when you're laying out foundation forms or walls, 1/2" (or 10mm) is generally the best precision you'll get. Look at industry tolerances. Most building materials aren't even accurate to a greater degree. 5/8" gypsum board is +/- 1/32", especially in humid regions; the 3 5/8" steel stud flanges clearly bend +/- 1/4" (sometimes I wonder if some architects have ever held a steel stud, much less built a wall). Add drywall compound (2x1/8") and paint (2x20 mils or about 3/64"), and that wall composite that you're spending valuable time to dimension correctly at 4 7/8" thick can never really be built that size... it's always over 5". Using wood? Good luck getting even close to that!

Using dimensions like 12'-4 37/64" just makes you look like you don't know what your doing. The contractor (who may have a 6th grade education) is either going to inaccurately round it off, or dismiss the dimensions altogether as ramblings of a madman, and build what they think is right. And I haven't even mentioned buildings that are out-of-square, warped, bowed, racked, or seismically shifted. This applies to new AND existing structures. Try specifying the need for 1/64" accuracy in your specs... be sure to point it out at pre-bid... and you will notice that your cost just went up 400%.

I know that the right thing is to adjust all of the objects in your model to be placed in a vertex within a reasonable grid. However, sometimes we divide things by 3 or 5 or some other prime, or we draw a circle, and that's blown away. Do you Teamwork with another architect, perhaps a less-precise designer (who's probably the one really making the money for the firm)? Then you've seen space plans get shifted around by free-hand increments in the 11th hour before a deadline. The right thing is to fix them all, but, quite frankly, there isn't enough money, time, or people who care.

All this precision doesn't add any value, and certainly doesn't put food on the table, or keep the doors open. Architects are being marginalized more every day by contractors, fabricators, and developers. I feel like we're racing to our own extinction having conversations like this. We need tools that make us faster, more free, more profitable. I don't want to be a digital janitor or BIM babysitter. I want to do what needs to be done to get it built. Just round the darn dimension and go home and hug your kids!

[Anonymous]

Da3dalus wrote:
Just to add to the cacophony... I'm in the school that says my job is to create instructions for the contractor to use in constructing the building that I've designed. The model is not the building. I always have a very tight budget to complete these drawings. Therefore, rounding, "+/-" and nudging are necessary to create a clean, readable set of instructions in a reasonable amount of time.

Virtually no contractor is capable of comprehending anything smaller than 1/8", and when you're laying out foundation forms or walls, 1/2" (or 10mm) is generally the best precision you'll get. Look at industry tolerances. Most building materials aren't even accurate to a greater degree. 5/8" gypsum board is +/- 1/32", especially in humid regions; the 3 5/8" steel stud flanges clearly bend +/- 1/4" (sometimes I wonder if some architects have ever held a steel stud, much less built a wall). Add drywall compound (2x1/8") and paint (2x20 mils or about 3/64"), and that wall composite that you're spending valuable time to dimension correctly at 4 7/8" thick can never really be built that size... it's always over 5". Using wood? Good luck getting even close to that!

Using dimensions like 12'-4 37/64" just makes you look like you don't know what your doing. The contractor (who may have a 6th grade education) is either going to inaccurately round it off, or dismiss the dimensions altogether as ramblings of a madman, and build what they think is right. And I haven't even mentioned buildings that are out-of-square, warped, bowed, racked, or seismically shifted. This applies to new AND existing structures. Try specifying the need for 1/64" accuracy in your specs... be sure to point it out at pre-bid... and you will notice that your cost just went up 400%.

I know that the right thing is to adjust all of the objects in your model to be placed in a vertex within a reasonable grid. However, sometimes we divide things by 3 or 5 or some other prime, or we draw a circle, and that's blown away. Do you Teamwork with another architect, perhaps a less-precise designer (who's probably the one really making the money for the firm)? Then you've seen space plans get shifted around by free-hand increments in the 11th hour before a deadline. The right thing is to fix them all, but, quite frankly, there isn't enough money, time, or people who care.

All this precision doesn't add any value, and certainly doesn't put food on the table, or keep the doors open. Architects are being marginalized more every day by contractors, fabricators, and developers. I feel like we're racing to our own extinction having conversations like this. We need tools that make us faster, more free, more profitable. I don't want to be a digital janitor or BIM babysitter. I want to do what needs to be done to get it built. Just round the darn dimension and go home and hug your kids!

At 35yrs of being an articulate and somewhat pedantic, (but realistic) design/build contractor....I say: RIGHT ON!