Forums >> General Discussion >> Revit Project Management >> Needed, Opinions on CMU wall widths

Rehler

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Good morning All,

We are having a bit of a war in my office considering the proper way to model cmu block walls in Revit.  I believe that everything should be modelled accurately, ie a 6" cmu block wall is given a width of 5 5/8".  Others in the office want to implement Autocad "fudges" to create even dimension everywhere by giving the 6" cmu block wall a width of 6".  I would prefer to model everything accurately and then create the model intelligently to keep fractional dimensions to a minimum, but would like others opinions who have created projects with cmu block walls.

Thanks in advance for your time and opinions!

Randy Ehler

Austin, tX

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WWHub

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We too have had this discussion in our office.  While I agree that you should draw accurately in Revit, CMU has some special conditions.  CMU is really a nominal sized product and is coursed to include the joints.  In addition, CMU has a lot of tolerance associated with it.  For those reasons, CMU has allways be drawn and dimensioned to its nominal sizes.

Think about it... If you have a 10' x 10' block building, do you really dimension it as 9'-11 5/8" square and expect it to be built to that dimension.  Rediculous!  The mason lays it out 10'x10' and the joints are what they are to achieve that.  If we have to dimensio to only one side of the joint, what happens to intersecting walls?  Which side of the wall to you dimension to?

This is not a CAD/Revit issue.  This is a construction industry standard.  CMU is always dimensioned nominally and as such, it should be modeled the same way.

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teafoe5

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I agree that things should be modeled as accurately as possible however there are a lot of people that feel " an 8" cmu should be drawn 8".  I think that with Revits capabilities accuracy should be the main objective.  You could always dimensions to center of walls.

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CDWdavid

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I agree with WWHub, and like to add following reasons.

1. The revit does not show the grout joints, the CMU pattern is using 16" x 8".

2. The most important thing is how do you create your families for CMU construction. If all your door and window families are following masonry module, i.e. 8"x16", then you should use it accordingly.

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WWHub

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teafoe - What is important here?  You want to dimension to the center of the wall then what does the mason do in the field?  Move .5 X 7 5/8" off that for the wall face?  If you are going to model accurately then you better model each block with some twisted on each layer.  Block walls are not flat!!!!

I am a big proponent of model it like it is built but you need to document the project in a meaningful way that can be built.  Masonry is not steel, it is not drywall and it isn't even wood studs.  It is a very unique material that has a traditional dimensioning standard and that standard has always been nominal dimension only!  This is even more importan with brick which because of firing can be even less precise.

Keep your precise unit dimensions for details but model dimension it nominally in all views except special details.

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Rehler

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WWHUB, I completely agree with your example of the 10' x 10' building example, and I too would make the outside corner to corner length 10'.  Our issue is much more to do with paralell interior walls that happen to be constructed of cmu block.  The parallel cmu block walls have metal studs walls running perpendicularly between them, so there is no block module to be concerned with.  My stance is to model the walls the accurate width, then determine early which side of the wall is to be the dimensioned side, and then layout the remaining walls from there in order to obtain even dimensions. 

I realize it's a matter of opinion, and will vary from office to office, I was just hoping to get as many opinions as possible to make the right decision for our office standards.

Thanks again to you all!

Randy Ehler

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teafoe5

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WWHub.. You are absolutly correct.  I guess I wasn't that clear in my responce.  I agree with the fact that in plan the walls should be drawn in at 8" if it is an 8" CMU wall.  The centerline answer was just an option if they went that route which I have seen done before however I feel as you stated "Keep your precise unit dimensions for details but model dimension it nominally in all views except special details."  With Revits ability to be so precice it is hard to stick with industy "standards" for drafting in some aspects but as you said WWHub "what is more important here"  and I agree with you. 

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West1977

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I'm of the opinion that you model to the best of your ability with the most accuarate sizes.  I hate getting plans where cmu is 8" instead of true width.  It's just something that will always be talked about and debated though.  I could care less if there are fractions in the dimensions if that's the closest to the way it's going to be built.  it reall depends on the size of the building though also.  A 10'X10' square like WWHub said would be simple as he suggested, they are going to lay it out as a 10x10.  However if you are doing a large 15 story hotel, I would model it precise as possible because over a long run of 150' or so, that extra will add up.  Our firm is currently redrawing a complete set of plans for a contractor to build from considering the firm that designed the hotel in Atlanta used all whole dimensions like idiots.  ie...interior walls were called out as 5" instead of 4-7/8", that adds up over a long run of dimensions and things can get realy whacky when the building starts.  Just my two cents, I will never be convinced modeling to nominal sizes is a good practice.  I also realize that there is a split over which way people want it done and I think there always will be.

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WWHub

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Masonry is completely different than wood stud walls.  Nominal dimensions for masonry has always been used for plan dimensions.  Stud walls should always be just dimensioned to one side or the other or if you have to dimension to both sides, then you include the actual stud dimension.  Masonry does not really lay up "true" like studs do (especially metal).  Each masonry piece may be laid slightly twisted so the real wall thickness is nevr the "true" unit thickness.  If you have a composite wall, then model the masonry correct from the outside of the wall.

If you follow the above, every building will be true and there will be no growth due to dimensioning.

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