BILT Speaker

BILT Speaker
RevitCat - Revit Consultant

Saturday 17 April 2021

Cut with Voids When Loaded - 'Cuts Geometry' Postscript

Following my earlier blog post on Cut with Void When Loaded in Revit, I have discovered another subtle exception to the rule:

It does not work properly with the new Revit 2021 feature "Void Cuts in Family Geometry" that allows you to turn the 'cutting capability' voids on/off in a family.  NB. This is sometimes referred to as turning off Void visibility, which is misleading.

Void in Family Editor

Here is a workflow that demonstrates the confusing behaviour:

  • In the family editor, create a new Generic Model family
  • Tick the 'Cuts with Void When loaded' family property
  • Create a solid with two more intersecting solids
  • Change the two outside solids to voids 
  • The voids will not cut the solid - this is a deliberate technique to carefully control what cuts what
  • Use the 'Cut' command to cut one of the voids from the solid (only one)
  • Select the visible void and link its 'Cut Geometry' property to a parameter - say "Cut Rect"
  • Select the invisible void (that is cutting the solid)
  • link its 'Cut Geometry' property to another parameter - say "Cut Cylinder"
  • In theory, this should allow you to turn off 'cutting capability' of each void independently, once in the project - and hence whether they cut or not.

Test this in the Family Editor

  • With both voids 'cuttable', the cylinder cuts but the rectangular void does not (as expected) - this is because the rectangular void was never told to cut the solid, so it has no effect in the family

  • Turn off the 'cutting capability' of the cylinder - it no longer cuts the solid;  it actually becomes visible, which may seem contradictory - but that is typical Revit behaviour (voids not cutting anything show orange;  voids already cutting a solid disappear)

Switch the cutting properties around so the cylinder can cut but the rectangular cannot - visually it looks the same as having both properties ticked.

 Voids in the Project

From my earlier blog post on Cut with Void When Loaded in Revit, we know that in order for it to work in a project, the cutting void must be set to not actually cut anything in the family - as the rectangular void is set up.
  • Load the family into a project

  • Place the family onto an element that it intersect with
  • Both 'Cut Geometry' checkboxes ticked

  • Untick both checkboxes, so the cylinder void is no longer cutting the family solid (rectangular void does not cut it regardless)
  • Both voids are ghosted when the family is selected, or in pre-selection

  • Use the project 'Cut geometry' command with the host element and family
  • Both voids will cut the host element (neither void is cutting the family solid)

  • Tick the 'Cut Rect' checkbox -
    • The cylinder is not cutting the family solid, so it cuts the host element in the project (this may not be what you want, but it cannot be avoided!)
    • the rectangular void is not cutting the family void, so it cuts the host

  • Tick both boxes - only the rectangular void cuts the host (as it is not cutting the family solid)
    • The cylinder now cuts the family solid but not the host (and is no longer visibly ghosted)


  • If the void cuts a solid in the family, it cannot cut an element in the project using the 'Cuts with Void When loaded' family property
  • If the void cuts a solid in the family,the new (in v2021) 'Cut Geometry' property has the potential to work in a project
  • If the void does not cut a solid in the family, it can cut an element in the project using the 'Cuts with Void When loaded' family property - but only when you use the 'Cut' command in the project
  • If the void does not cut a solid in the family,the new (in v2021) 'Cut Geometry' property has absolutely no effect in the project

This probably makes sense if you think really hard about decisions the programmers had to make about what is possible and how it might work.

However, it is mighty confusing for the end user.

To make matters worse, we now have two entirely different 'Cut Geometry' functions in Revit:

  • 'Cut Geometry' property in the family - a checkbox
  • 'Cut Geometry' command:
    • in the family- where you actively select which elements cut each other
    • in the project - where you actively select which family cuts which element but the results depend on all kinds of things in the family (as described above).

All clear now?  Or still confused?

Thursday 1 April 2021

Rustic Railings in Revit

There has been a lot of talk over the years about just how hard the Revit stair and railing tools are to work with.

I decided to do an experiment - and see how long it took to build an actual stair and railing vs building the same thing in Revit.

I chose to build a rustic-style stair as it was outdoors in a wild garden setting.

Rustic Stair and Railing Hackathon

I thought I had better give Revit a fighting chance by not zeroing in on one of Revit's biggest railing weaknesses:  "Baluster Spacing"

  • So I decided not to include any balusters at all.  

Technical Details

  • The stairs were made from hand-hewn sandstone, with irregular shapes and slightly differing tread widths;  riser heights were near enough the same for each step.  Stones were carved to exact size and placed without mortar - exactly how the ancient Egyptians, Mayans, Aztecs et al worked their stone structures.
  • Railing was made from locally sourced Melaleuca timber - hand-cut on site:  Two posts and one 'Top Rail', all sourced from the same tree.  The top post and handrail were left to cure in the open for several weeks;  the lower post was cut and installed the next day.
  • The handrail was fixed to the posts with tuppenny nails.
  • Real stairs and railings were built without any drawings - I couldn't wait for those to be finished.
  • The virtual stairs/railings were created using the "New" stair tools (post Revit 2013) & the "Old" railing tools (circa v2 with minor improvements in v2013)

Finished Product

The finished stair and railing

Unfortunately I don't have an image from Revit, because it was created in a later version that I could not open with my current version of Revit.

The Stats

  • The real stair took approximately 18 months, done a few hours at a time at weekends.
  • The real handrail was build about a year later - it took approximately 2 months, again done at weekends.
  • The virtual stair took 5.5 years, including waiting time between Revit versions - hoping that problems encountered had been fixed in the next version.
  • The virtual railing is still unfinished, awaiting software improvements.

Problems Encountered

  • The lower railing post was obviously installed too quickly after cutting, as it started to sprout a few weeks later (inadequate curing time).
  • I really struggled with applying the virtual stair hand-cut stone materials to the treads, especially in 2D plans.
  • Without any balusters on the virtual railing, the 'Building Inspector' would not give approval to the railing.

The Winner

Hands down winner was the real stair/railing:

  • It was so much easier and quicker to build the real thing than attempting a virtual model.
  • It was very therapeutic working manually on the stone and timber at weekends after a hard week of Reviteering.
  • It was ever so slightly less therapeutic grappling with the virtual tools for stairs and railings in Revit.


1st April 2021 (Australia).