Families – Planes

This is the first on a series of posts about Revit families so I’ll take a moment to describe where I’m coming from when I write these. I am going to take for granted that the reader knows how to create families and how to use them in Revit. The reason for this is that Revit comes with some rather nice family tutorials and I don’t want to cover that ground again. Instead I’m going to go over some quick points that I have noticed many beginner tutorials don’t cover.


There are 2 kinds of references in Revit families: Planes and Lines.

The Difference

There is a huge difference between the two and the difference is this: to Revit Planes are infinite in length while Lines have a start and end point. So what? Well it makes a difference if your trying to create a family that has a variable angle (rotation) to part of it. Say a north arrow that also shows a project north at some variable angle off true north. If you attach your project north line-work to an infinite line and then rotate that line what point does it rotate around? Revit needs to know the centre point of the angle that is changing in order for a consistent result to happen. Since a Reference Plane is infinite in length, the centre point can be anywhere along the plane. The result is the plane will rotate but the project north arrow will appear to move away from the true north arrow but never the same way twice.

There are other differences but this is the big one.


Reference planes are the skeleton that give the family it’s form, while labelled dimensions are the muscles that move it. Everything else should be attached to the skeleton.

When you select a plane there are 3 important properties you can edit in the Properties Pallete:

  • Name – this property is for making editing the family easier. When you name a reference plane, the name will appear in the pull down list when you are specifying a new work plane.
  • Is reference – this property will affect how the family is dimensioned IN A PROJECT. If this is set to “Not a Reference”, the plane will not be able to be dimensioned to. It will be completely invisible when loaded into a project. “Strong” and “Weak” references indicate which plane will be shown by Revit first. To dimension to a weak reference you will have to tab to it. Strong references will always be highlighted first. Any other value here (and you don’t need to use just the ones given) are for maintaining dimensions when switching to a different family. For example, if you have all your windows dimensioned to the “Center (Left/Right)” plane and you change from one window type to another, Revit will re-attach the dimension. If there is no “Center (Left/Right)” plane in the new window type the dimension will be deleted.
  • Defines Origin – you need to specify 3 planes with the property. Where these 3 planes intersect will align with the mouse cursor when placing the family in a project.

There is also the Wall Closure and Scope Box properties. Wall Closure specifies where the wall will wrap in a door or window family. I never use this property since I use drafting views when detailing jamb or sills. I’m not sure why scope box is there you can’t create scope boxes in the family editor.

Here are some more tips to make sure your families are stable and flex properly:

  • always lock geometry to reference planes, labelled dimensions should always connect to planes not geometry.
  • when constraining ref planes with EQ, create the ref planes at equal distances.
  • when drawing ref planes the left side is always positive. The name always appears at the end point.

That’s it for this week. In the next few posts I’ll cover reference lines, controls, nested families and auto-dimensions.

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Revit and Building Information Modeling