Support for HVAC maintenence zone export


We are planning to support (HVAC)maintenence zone export. Maintenance zone is modeled to our objects and customers has asked us to export them to IFC. This is how we do it now (not released version). Please see MaintenanceZoneIFC4.ifc (14.1 KB)

  • IFC4 exported as IfcBuildingElementProxy/PROVISIONFORSPACE
  • can consist of multiple separate zones
  • transparency is set

This is how it shows up in most of the viewers:

There you can see clearly how zones now don’t have references to main part.

What is missing now is reference from zone(s) to part that owns maintenance zones. We are planning to have that reference with IfcGroup.

Open questions are:

  • Is IfcGroup right way to make such connection?
  • Is it worth of having zones separately or should we export one object’s all maintenance zones as one zone?
  • How should we export maintenance zones in IFC2x3 since it is lacking PROVISIONFORSPACE. We have to support also IFC2x3 (it is widely used). Could we just set ObjectType == PROVISIONFORSPACE?

I think main thing is to find out best way to model such zones so that collision checks in viewers could do their jobs.


MR 2020-03-18 > Please see a test how IfcGroup can be used AllInOneGroup.ifc
(24.0 KB). A pic how Solibri shows it:

There is other ways to group main part and zones also; we just have to find way that is most usable and convenient to receivers.

Kind regards,
Marko Ripatti

Have you considered adding a Clearance shape representation to your equipment object directly? That would forego the need to create 4 maintenance zones and group them. Also, Clearance representations are explicitly for the purpose so that collision checks can be performed.

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I think, it’s possible to use for maintenance purposes in IFC2x3TC2 BoundingBox and for IFC4.2 Clearance Geometry.

Thanks both! We will definitely take a look in that direction.

Hi @marko.ripatti, I agree with the other comments, look into clearance geometry, see e.g.

However best if you can check how others, like Solibri, etc. supports multiple shape representations - here 1 “body” representation and 1 “clearance” representation.


At the moment Solibri doesn’t support multiple representations, but we’re following this discussion with interest.


If it helps, from my findings, Revit does support import of multiple representations, but doesn’t distinguish which is which. Revit does not support export of multiple representations.

The BlenderBIM Add-on supports export of multiple representations, and also supports import of multiple representations, but the import currently doesn’t distinguish between them.

Good to know, thanks. We are operating with own IFC exporter that is used also in our AutoCAD based solution so in that sense it is all in our hands. I’ll get back when we have sorted out what it requires to support multiple presentation.

MR 2020-03-24> Now we have a sample how to use clearance geometry. In that sample we use bounding box but if we go that way bounding box will be replaced by any number of solids. Please see MaintenanceZoneIFC4_ver2.ifc (8.0 KB)

At least FZKViewer can show body + clearance representation:


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Looks good to me.

@Moult could you test how BlenderBIM Add-on reacts to MaintenanceZoneIFC4_ver2.ifc? To me it showed a real quick exit… maybe there is something wrong in our sample.

@trondholen could you also test same sample with DDS viewer. To me it seems that viewer did not like much that sample.

@marko.ripatti - tested, and I can replicate the problem :slight_smile: I believe it is a bug in IfcOpenShell causing the crash. The bug has been documented and I see that @aothms is already helping to fix it!

Glancing at the STEP source, though, it looks OK :slight_smile: I’ll keep you posted when the crash is fixed!

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@marko.ripatti bug has been fixed and will be available in the next release. See below:

Great! I hope we can get back soon with new maintenance zone test files.


Please find attached sample of switchboards with maintenance zones (as clearance geometry) ClearanceGeometry.ifc (16.4 KB) There is also transparency setting in those geometries but seems that at least FZKViewer does not react to transparency so it could be also that our model is not correct.
BIMCollab Zoom shows our clearance geometry presentation correctly (exist and transparency is there) but I don’t know if there is control over those zones (to show or not).

Basic question is if this is correct way to present maintenance zones (as clearance geometry) and obviously could viewers and model checkers utilize those zones.

@pasi.paasiala is there any demands/wishes of maintenance zones from your customers?

My guess is that transparency has the same behavior as color. Very much variables in various places.

We ended up to use Clearance geometry ( as Thomas suggested.

Seems that at least BIMCollab Zoom can show clearance representation as we now export it. FZKViewer also but could not find how to make it show transparency and color.

End user will have control over if clearance representation is exported or not so in that sense we expect no troubles using those even when we don’t have user agreement how to export clearance zones.

(IFC) Importers could use attached file for testing purposes. We can deliver more samples if needed.
M-zones.ifc (8.4 KB)

Our plan is to publish this (export) feature in next release at the later part of this year if community does not totally disagree how clearance zones export should be done.

All good input and valuable input for the members of BuildingSmart to put on their list for testing & certification !


  • color appearence
  • maintain of object transparency
  • minimum demands time importing

It’s crucial to explore different techniques and approaches when it comes to modeling maintenance zones. Finding the most practical and user-friendly solution will ultimately benefit both you and the recipients of your work.