That's a tough one. When this happens, there is no level to select in the drop-down? Or you select the level, but you see absolutely nothing? Or not what you were expecting?

If it's more like the latter, I've found some elements in an underlay can obscure what should be visible. For instance, there are times I've selected a 2nd floor as an underlay, and elements of the roof (above the 2nd floor) obscure the 2nd floor. Keep in mind that you can hide elements of an underlay. So in that instance, I'd attempt to select the roof element that is obscuring the other elements and hide it with a graphic override.

Thanks for reply
Its the latter. I went and had a play in the job where this was happening and there was nothing obscuring the underlay. What I did do was changed the View Range Top level and offset then changed it back again and it all came good with the effected underlay now working. Was almost like a Refresh. I will wait till it happens again to see if Refresh trick works again.

Good to know. So in that instance, it sounds purely like a Revit bug? I know it's a drag, but if it's reproducible, you might consider filing a support request to let them know about it.

View range has a HUGE impact on underlays. Most people arent aware (so even if it was just a fluke, keep this as an fyi): An object will NOT show up in an underlay, if its entents also occur in the views View range. For instance: Draw a wall on the first floor. Then put a floor on the second floor, and GO to the second floor plan. You cant see the wall, right? The floor blocks it. Now, turn the underlay on, and youll see the wall. NOW, adjust the view range of the second floor plan, so it goes ALL THE WAY DOWN TO THE FIRST FLOOR. The wall will come out of the underlay... But you still cant see it. The floor still blocks it from the view on the second floor, but the underlay eliminated it, because it knows it "should" show on the plan itself.

As always, this is golden. But I'm not sure I got it yet, can you clarify this sentence? Thanks.

Post edited. It was a typo. What i meant was: Model a wall on the first floor. Then model a floor on Level 2. Then go to the Second Floor Plan, and (obviously) you wont see the wall. Then follow the above...

Thanks. Seems obvious what you meant now that I see it, LOL.

Resurrecting this thread as it seems relevant to my current problem. I'm trying to wrap my head around underlays and view depths. I have a project I'm working on where the information that is being displayed is, well, a bit random. So to try and figure things out in my head I've created a very basic project to see if I can recreate the issue. I have attached the file for reference - its in RVT 2012.

Okay, so what's the problem? Well, if I underlay the floor below any floor it seems to be fine but if I try to say underlay level 2 under level 1 it doesn't work. Using a matrix to show the what works and what doesn't I get the following;

The view range settings are the same for all levels and are the default settings.

Can anyone explain to me why I'm seeing these odd results? Essentially I want to be able to use any level as an underlay on any other level. Currently the only level that behaves in that way is Level 3.

I've tried making changes to the view range but it doesn't seem to make any difference.

Any help pointers greatly appreciated.

Cheers

Keith.

Hide the Floors to see the underlay(s)

Keith,

I was recently battling this and looked at your file. I'm surprise no one has responded. The Revit help file (for 2014) description for View Properties of Underlay is written like this:

"Halftone/Underlay