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Monday, 7 January 2019

Weird Railing Stuff - part 15 - Railing Lateral Offsets

I started out writing about the 'Handrail Hand Clearance' property of Railings in Revit - then I realised that it would involve analysing all of the related lateral offset properties associated with Railings and each different component.  It turns out to be a real "dog's breakfast", with at least six different ways to offset railing components, with minimal consistency between them all.  So I decided to document that first before looking at how it all affects 'Hand Clearance'.
Colour coded railing sub-elements
The above view of a railing is colour coded to help distinguish each sub-element; it is set at an oblique angle so that offsets are clear to see in the following examples with exaggerated offsets of 500mm.

A Dog's Breakfast

Railing Sketch line.

When a railing is placed automatically on a stair, it has a sketch line, that is typically on the edge of the run/landing.  All railing lateral offsets relate back to this sketch line location.

1.  Offset From Path


This is an instance property, which is applied to the whole railing and all its sub-elements.  
It represents a notional centreline of the railing, offset laterally (sideways) from the railing sketch line, which is placed on the edge of stair runs and landings by default.


Unfortunately there is a built-in system default value of 25.4mm, which is one inch.  The logic to this is obscure - it only works if your top rail happens to be 50.8mm (two inches), and where the face of the top rail needs to align exactly with the edge of the run/landing.  Why is this so bad?
  • This never, ever works in the metric world (all but two countries in the world) - even if we have a 50mm top rail there is still an 0.8mm discrepancy every time; Occasionally it might suit a situation in the imperial world, as described above;
  • This never works when the stair abuts a wall (metric or imperial) - see what happens to supports later on.

This default value is infuriating - as you have to correct every single stair railing after placement.  In my opinion it should be a default that we can control in some way (either a 'last placed' setting or in the Revit.ini file);  alternatively it should be a Type property rather than instance.  Please vote here on Revit Ideas if you agree with me - if this blog has helped you out, then please help me out by voting.

2.  Old-Style horizontal rails


The old Type Property dialog box for horizontal rail structure has a separate 'Offset' property for each rail element.  This does not used the word 'lateral' anywhere on the dialog box, so you have to guess which of the three possible directions it will offset (x, y or z), as well as which is positive or negative.

3. Baluster Placement (Individual Balusters)


The Baluster Placement dialog has a separate 'Offset' property for each baluster element.  This does not used the word 'lateral' on the dialog box, so you have to guess that it is a lateral offset property - although there are also Base and Top offsets, so it is easier to identify.


Warning:  This individual Baluster Offset property goes in the reverse direction to most other offsets:  A positive value pushes the baluster outside the stair, while a negative value goes in towards the stair - this is inconsistent with most other railing offsets.

4.   Post Placements

Railing posts are similar to Balusters (with the same reverse direction offset)

5.  Baluster Offset (and Top/Handrail)

Back in the Railing Type Property dialog box, there is another property called 'Baluster Offset' - another guessing game ensues.

This can give very unpredictable results.  It will laterally offset all of the balusters by the same amount;  it does not affect the horizontal rail structure.  With the old style railings, it was confusing enough because the individual Offset goes one way, and the overall baluster offset goes the other way. However, with the new style railings* it is almost incomprehensible :
  • The balusters will all be offset laterally by the same amount.  Unless . . . .
  • If an individual baluster offset value has been applied, it is cumulative, so the individual is added to the master baluster offset property (bearing in mind that a positive value for one may cancel out a negative value in the other).
  • Old style horizontal rails will not be affected (they get left behind).
  • New style 'Top Rails' will be offset.
  • New style 'Handrails' will be offset.


The net result of all this is that the Baluster Offset property may work as a Type control offset for the whole railing, provided that you don't have any old style mid rails - in that case you have to offset each of those in the Rail Structure dialog box.

* New style railings were introduced from Revit 2013 onwards, but old style railings were not automatically upgraded - only if you've swapped to the new style railings!  You may still have old-style railings in your projects.

5A.  Rest

Are you still following all this?   If not, (or you have a headache) just have a rest or lie down for a few minutes, before moving on to the next one.  I can't say it gets any better . . .
Deconstructed Railing

6.  Handrail

New style railing Types have handrail properties - these include "Lateral Offset" for each handrail, which are greyed out. 

The Lateral Offsets are calculated by the system, depending on the Handrail type properties.  This represents the offset of the Handrail centreline from the notional Railing centreline (which is in turn affected by the "Offset from Path" property . . .)
Refer to Rail Hand Clearance Property for how this is calculated.

If you change the 'Hand Clearance' property it will move the centreline location of the Handrail relative to the overall Railing.
  • This has to be done in the Handrail Type properties dialog box, not in the Railing properties.

7.  Right Handrail

The above example assumes a handrail is set to 'Left' Position.  If it is set to 'Right', the whole handrail is mirrored and offsets outside the stair.

8.  Top Rail

Top Rails also have a 'Hand Clearance' property, but unlike Handrails, this is not displayed as a Lateral Offset in the Railing Type properties.


The Hand Clearance property of of the Top Rail most assuredly does affect its Lateral Offset - so it would be mighty useful to have that property displayed, even if you want the Lateral Offset to be set to zero most of the time.

Why oh why is it missing?


One possible reason it is missing might be that the offset direction is the opposite to Handrails - a positive Hand Clearance on a Top Rail would give a negative Lateral Offset.

9.  Sketch Offsets

I would not be surprised if there are other Offset properties that I have missed.
There is at least one more way to move Railings, aside from playing with the properties:
  • Edit the stair sketch and 'Offset' the sketch lines from their original location.
  • I would not recommend doing this on stairs without good reason, as it would make the properties even more confusing.
  • If the sketch lines go outside the run or landing (laterally), you would most likely encounter hosting and height problems - so that is not advisable.


If you are confused by all this, it is hardly surprising.  I will try to shed some light on how to manage these offset properties in future blog posts. . . . .


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