What is a Revit ʼPermanent Dimensionʼ?
Short Answer
A Revit permanent dimension is a model-based annotation created with the Aligned Dimension tool that stays associated with referenced elements as the design changes. It is the standard professional method for documenting controlled distances in plans, sections, and elevations. It only works reliably when the dimension references remain valid.
What You Need to Know Before
Warning: permanent dimensions in Revit can lose references if you dimension temporary geometry, weak references, or elements that are later replaced instead of edited. This often causes witness lines to detach or dimensions to display errors after model changes.
How to Create a Revit Permanent Dimension
Command: Aligned Dimension
Shortcut: DI
Quick Steps:
- On the Ribbon > Annotate tab > Dimension panel, click Aligned.
- Select the element references you want to dimension, such as wall faces, grids, or core faces.
- Click to place the dimension line, then use the Options Bar to set a real option such as Prefer: Wall centerlines / Wall faces / Core centerlines / Core faces.
Variables & Settings
Key Setting: Prefer option in the Options Bar
Expert Setting: This controls what Revit dimensions to on compound elements like walls. Using Core Faces or Core Centerlines is the most reliable choice for construction documentation because finish layers may change during design and break consistency.
Why it Fails
- Cause 1 (Geometry): The dimension is attached to non-persistent references, such as temporary faces or geometry that changes shape after edits.
- Cause 2 (Layers/Locks): Linked models, pinned elements, or edited wall layers can prevent stable dimension references or cause unexpected witness line behavior.
- Cause 3 (Command/Logic): The wrong reference preference was used, such as wall faces instead of core faces, so later wall type edits make the permanent dimension less dependable.
Quick Fix & Best Practice
- Quick Fix: Recreate the dimension with Aligned Dimension and set Prefer to Core Faces before selecting references.
- Manager’s Verdict: Use permanent dimensions for final documentation and controlled layout references, but avoid dimensioning unstable finish faces early in design development.
FAQ
What is the difference between temporary and permanent dimensions in Revit?
Temporary dimensions appear during selection and editing, while permanent dimensions are placed annotations used in documentation.
Can a Revit permanent dimension update automatically?
Yes, it updates when referenced model elements move, as long as the references remain valid.
Can you lock a permanent dimension in Revit?
Yes, you can lock a permanent dimension to constrain element positions when appropriate.
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