Monday, April 30, 2018

Warning - Face Based Content Moves Vertically in Revit

Anyone who develops MEP models in Revit knows that only face-based content works due to the limitations of working within the context of linked architectural and structural models. However, I find a lot of people do not know about a subtle issue that causes things like receptacles to move vertically at some point during the project.


Read on to learn more...
Notice the three receptacles pointed out in the iamge above. They are also shown in the plan view below. Well, on a side note, two of them are shown. Because two are aligned vertically, you cannot see the lower one. The electrical content LHB developed, and sold by CTC Express Tools, has a really nice way to deal with this. Check out this previous post for more:




When a face-based family is placed, it can have a default offset relative to the floor (based on the current plan view) as shown in  the image below.

This same face-based content will maintain its position relative to the floor if the wall is adjusted, as shown in the next image, with one big exception!

When the face-based family is placed on a linked wall, which is all the time for MEP, the content moves relative to the bottom of the wall as shown in the image below! This is very bad.

To be clear, the content is originally placed correctly, relative to the floor, regardless of the current bottom of wall position. However, if that bottom of wall position is adjusted (by the architect or structural) after the fact, then the face-based content (receptacles, data, thermostats, etc.) all move.

I see this happen when the exterior walls are tilt up precast and the consulting structural engineer realizes that, in northern Minnesota, where I live, frost is five feet deep mid-winter, so footings are often six feet deep. Thus, moving the footings and bottom of precast walls down sometime mid-project will cause all face-based MEP families (any FB families, really) to move as well. This can also happen if step footings are added along a sloped grade.

Another example is a new, or existing, building with various floor elevations at the same level. For example, at Level 1 a third of the plan is three steps lower to align with grade or another adjacent building.

This is something everyone, Architects, Interiors, Structural and MEP need to be aware of to prevent unwanted mistakes to be introduced into the project. In this case, communication is key! Because clash detection will likely not help here.

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7 comments:

  1. Change in location is something that can be picked up through QC and the use of a model compare add-in (Metamorphosis), Navisworks model compare or BIM 360 model version compare.

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  2. Thanks for sharing, Saji. Your point is valid!

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  3. Great information.
    Do you have any ideas why a face base receptacles would move sideways along a wall and still be hosted?

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    1. It can happen when the wall extents are adjusted. One end may have been trimmed, or extended. Even doing something like adjusting the sketch associated with the wall can do this, particularly if the sketch includes (even temporarily) lines that extend beyond the "ends" of the wall.

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    2. Thanks for sharing metis. I had tried several of those things before replying and could not get a FB family to move. But clearly there are many things that could come into play. Maybe if those types of changes happen in a linked model?

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    3. In theory it should be more stable in a linked model, but it might not be. It's easy to forget that Revit has a coordinate system, and that there is an xyz origin point for each element, which then interacts with other elements. Usually the location of an object is contained within its "physical" extents, but sometimes it's outside of those bounds due to editing, or intentional error correction or management (I often build families that have reference planes that don't "exist" because they let me define relationships within the family more efficiently, Revit at a system level seems to do similar things)
      When you have something related to a linked model Revit assigns things positions within your model as associated with an element ID in the link. It's unclear how much of the position of that element Revit pulls from the linked model - I suspect it looks at limited portions, maybe only the element ID, object origin and intended host face and sees if that lines up with the host point and face in the model.

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  4. No, I cannot think of any reason. Perhaps they are being selected accidentally in another view and moved? If you figure it out, let me know what it was.

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