Floor based family attached to the BOTTOM of the floor

[LOESCH_PK]

Hey guys, I've got a strange problem. I wanted to make a floor based family, which parameters would all refer to the bottom face of that floor. It is a smoke exhaust window, and I would like it's placement height to be always the same (in reference to the bottom of the floor!). And using parameters to lock it to the bottom in the family editor initially looks like it does the job. It works when I change the floor type, but the moment I use the modify sub elements tool to modify the top of the floor the family "forgets" it was hosted to the bottom, and behaves like it's hosted to a level that equals the top - the default thickness ot the floor.

Any way to work this out? Changing the insertion point plane to a plane locked to the bottom of the floor, just puts the whole family on top of the floor. Attaching the parameters to the level in the family doesn't work either. A solution would be to make a family not hosted to the floor and just cutting it, but that is a bit counter-intuitive. 

[cbcarch]

Perhaps usw a Reference Plane at the bottom of the slab in the project to align the smoke window to?

Not "automatic"; may not be a big deal, depending on how many of these windows are in the job?

[LOESCH_PK]

Well for now I've used a family not hosted to floor, but to a level, and used parameters that reference to that level, so they are all at the same height. For the scale at the moment this is OK, just have to use 3 parameters, and make additional types if those windows are at a different height, and also add geometry and cut geometry with the floor. But it would be nice if it worked when hosted on the roofs.

[ToanDN]

You can use a face based family and pick the bottom of a floor or a roof to host the family.  Works best in 3D.

[LOESCH_PK]

Good idea. I'll try that.