Can you accurately schedule wall lenghts?

[torpedorrr]

I was doing the schedule tutorials, and did some testing (see attached image). It seems Revit gives me the correct area and volume for the walls (they are 1 m tall) but their lenght is off by half a wall´s width. I suppose it has to do with measuring wall centre lines, but is there a way to get correct wall lenghts?

Thanks

[Teresa.Martin]

Dear Augi Member;
I am getting the correct wall lengths on my schedule, but I believe you might be actually talking about the length of a wall as it turns the corner?
Revit typically uses the centerline of the wall, or center of core (structure) for linear length.
I believe that is how it is doing the calculation.
Best regards,
Teresa Martin
Ideate Inc

[jeff.95551]

It seems the algorhythms they use are fairly simple. I think it is important to keep this in context, however: the numbers that come out of Revit are still far more accurate and have a higher tolerance than anything that a contractor is going to derive from the drawings. If we were using Revit to design the next Boeing Jumbojet, I'd be worried, but as a contractor, I can use these numbers with much more confidence than anything I can take off of them. In your example, you had 5% too much wall, but in a typical example, the intersections are a much smaller percentage. If you are within 2% on your areas, you will still have much more confidence than a builder has in his takeoffs - when I'm doing it the old fashioned way, I measure long, round up, then add some additional (between 3 and 10 percent) depending on the size of the project and my confidence in the drawings. With jobsite waste, inefficiencies, errors, etc., I usually end up very close. It would be great if Revit knew exactly, but until construction changes radically in its efficiency and production, it won't make any difference at all in the field.

[narlee]

Excellent perspective, Jeff.

Geof.

[torpedorrr]

I hadn´t thought about it that way, but you are right. Thanks for your insight, Jeff.

[DoTheBIM]

To answer the original question, No it is not possible to get accurate lengths in Revit through standard scheduling. Something may be possible through the API, but I haven't got into that yet to find out.

Agreed that Jeff's perspective is one way to look at it and only one way. Unfortunately for us (the company I work for), Jeff's perspective seems to have been the majority in the beginning stages of Revit development. It probably still is the the majority. While concrete and steel work it might be the norm to use centerlines for things.... using dimensional lumber it is not. I'm sure the factory is well aware of this, (or at least a 3rd party anyway) and someone is currently working on a solution. Anyway my point is that Jeff's perspective is entirely valid from an estimating point of view, but when looking at it from a prefabricated point of view, Revit just doesn't cut it... at least not in whole, you will need another program to get the job done efficiently.

[jeff.95551]

DotheBIM is right - if we ever get to a manufacturing model in construction, Revit will need to tighten up it's systems. I'd like to see it go there, but I've been in the business long enough that I'm not holding my breath. In my opinion, dimensional lumber is far more difficult to schedule - especially to do lumber takeoffs. If that is your goal, then you probably need to draw every 2x4, king stud, cripple, header, etc. If you are doing prefab and you're going to build 100 of the same wall, it's worth it. For one building, you're wasting your time - the framers won't even look at the drawings. They know how to frame a wall - and if they don't, your drawings aren't going to save them.

I think it also is worth thinking about the qualities of the materials you are trying to schedule. For drywall, area is a good measure. For stud walls, area doesn't help much. Length is more useful, and the extra 5% that the example wall is off probably is offset by the extra studs that are in the corner for nailers.

[aaronrumple]

DotheBIM is right - if we ever get to a manufacturing model in construction, Revit will need to tighten up it's systems....
We're there already. We just don't have the tools. I'm on my second panelized project (115,000 sf/4 stories.) For this project I'll be passing the model to the subs as we are not only the design portion of the project, but also the build. Our panel sub will just have to redraw everything for shops in AutoCAD.

[jeff.95551]

Don't a lot of those guys already have pretty sophisiticated routines in Autocad to layout the studs and setup the cut lists? Pulling the model from 3-d into Autocad for processing seems to me a pretty efficient way to go. We don't need all that information in the BIM - my files are huge already. What kind of project is it?

[aaronrumple]

Don't a lot of those guys already have pretty sophisiticated routines in Autocad to layout the studs and setup the cut lists? Pulling the model from 3-d into Autocad for processing seems to me a pretty efficient way to go. We don't need all that information in the BIM - my files are huge already. What kind of project is it?
Simple drafting routines, yes. Fancy cut lists? Not this company.
The point is that these walls will be drawn 3 times by 3 different companies. I'll draw them, structural will draw them (AutoCAD) for shear wall design. Then the panel company will draw them. Then I have to check them Then structural has to check them. On the least project, the Revit drawings proved to be the most accurate. Given the tight construction schedule, it would save a good 2 weeks if the Revit model were used for the panels. The project is student housing.

[DoTheBIM]

I'm in the same boat as Aaron. We're already there and have been for a long time. We've been doing panels for years, but only detail specialized walls (i.e. walls with sloped plates). We also want Revit to drive the design... as we are getting automated equipment that requires all panels be detailed. We are working on a solution to do so.