System Computed Height - what determines this?

[dbaldacchino]

Hi all,

Typically we leave the default setting for Room and Area settings to "At System Computed Height". This sets the "cut plane" for area calculations at some value, which is typically offset 0'-0" from the level. Or at least that's what it has done until today.....

I'm looking at a project where the system computed height is now 4'-0" above the levels. How does Revit determine this? The reason we discovered the issue was because we had a series of openings in the walls, set at 2'-6" above the level and the rooms kept "flowing" through. I kept raising the Bottom Offset until finally, at 4'-1", the rooms started behaving like I'd expect them. I also tried grouping the area in question and save it out to a file, but when opening this file, the system computed height went back to 0'-0", which indicates there's something in the project causing this. Once we set the Room and Area settings to "At Specified Height" of 0'-0", the rooms started recognizing their bounds and the areas calculated correctly. I've never had to change this manually before. Anyone run across this?

We also tried auditing the central file, resolved all warnings in the project pertaining to overlapping walls, room separation lines and rooms, but the issue remained.

[lev.lipkin]

System Computed Height : by default, is 4’ above the base level of the room. Suppose the room area includes a room separation line joined to a room-bounding wall that is lower than 4’ above the base level. In this case, the System Computed Height defaults to 0 (zero) to bound rooms by joined lower walls for that level. Hope this helps.

[dbaldacchino]

Thanks for the speedy reply Lev.

Unfortunately I cannot correlate what you're saying to an example. The System Computed Height (SCH) seems to be 0'-0" by default and then some other factor causes it to change to 4'-0". Take a look at this example....I have an opening at 1" base offset, Rooms don't flow through. Even without that low wall and separation line like you suggested, the SCH stays at 0'-0".

Now go to the little wall's properties and set it to 2'-1" instead of 2'-0" (it has a 2'-0" base offset too)....now the SCH seems to change to 4'-0". You can verify this by hanging the base offset of the opening to 4'-1" and the spaces don't flow through anymore.

[abarrette]

Do you have any sloping walls in the space... it might be an automatic detection of that surface. If I build a rectangular room with a canted wall built to meet the bottom of a vertical wall removing the canted wall increases the square footage. leads me to believe there is some sort of area justification (per BOMA?) happening there.

[dbaldacchino]

This doesn't really have to do with that....I'm talking about Revit's "assumed cut plane" to determine which are the bounding walls. In the posted example, there are no canted walls...it's just a simple example to illustrate that the SCH is coming in by default at 0'-0" and not at 4'-0". Also, in the actual project file, we have no walls that extend below Level 1 (no negative base offsets). I'm wondering if there's some other wall up on another higher level that is causing the SCH to be changed to 4'-0".

[lev.lipkin]

You are right: if room-bounding wall intersects 4' height in elevation and is not present at 0' height (above level), system computed height will be reset to 4' to account for wall.

Rule which I mentioned above (room separation joined to low wall) is applied only if there is no such wall (intersecting 4' elevation line and not 0' elevation line above level).

[dbaldacchino]

Thanks for the correction, I think I understand now. So in this project where the SCH has been set to 4' high, there's probably a wall on level 1 that has a base offset to some value greater than 0. When this happens, as soon as the top passes the 4' elevation from that level, the SCH changes to 4'. That's why in my posted example, as soon as I made the wall 2'-1"with a 2' offset (the room sep. line is not even required to demonstrate this), it caused the error since the top was at 4'-1". Similarly, a 10' wall will cause the SCH to change to 4'-0" as soon as you give it any offset, even as little as 1/128".

I guess we could just force the bounding height to be always 0' by not leaving it up to Revit to decide. We might make this change to our templates. Thanks again for looking into this!