How do you mirror a floor plan in Revit?

To mirror a floor plan in Revit, you select the desired elements and then use one of the two primary mirror tools: Mirror - Pick Axis (MM) or Mirror - Draw Axis (DM). These tools allow you to reflect selected geometry across a defined mirror line, either creating a copy or moving the original elements.

Here's a breakdown of how to mirror a floor plan effectively:

Understanding Revit's Mirror Tools

Revit offers two distinct methods for mirroring, depending on whether you have an existing line to use as a reflection axis or if you need to create one.

Feature	Mirror - Pick Axis (MM)	Mirror - Draw Axis (DM)
Purpose	Uses an existing line (e.g., wall, grid, reference plane) as the mirror axis.	Allows you to draw a new line to act as the mirror axis.
Shortcut	MM	DM
Best For	Reflecting elements symmetrically across an established architectural feature.	Creating a custom mirror line for unique reflection requirements.

Step-by-Step: Mirroring Floor Plan Elements

The process begins with selecting the elements you wish to mirror.

Method 1: Mirror Using an Existing Line (Pick Axis - MM)

This method is ideal when you have an existing architectural element or datum that can serve as your line of symmetry.

Select Elements: In a floor plan view, select all the elements you want to mirror. You can do this by:
- Clicking individual elements while holding Ctrl.
- Dragging a selection window around the desired area.
- Using Ctrl+A to select all visible elements in the current view.
Activate Tool: Navigate to the Modify tab on the Ribbon, then in the Modify panel, click on the Mirror (Pick Axis) icon (often depicted as two triangles reflecting over a line) or type the keyboard shortcut MM.
Define Mirror Axis: Move your cursor over an existing line that you want to use as the mirror axis (e.g., a wall centerline, a grid line, a reference plane). Click on this line to define it as the reflection axis.
Confirm Action: The selected elements will immediately be mirrored across the chosen axis.

Method 2: Mirror by Drawing a New Line (Draw Axis - DM)

This method provides flexibility to define any arbitrary line as your mirror axis.

Select Elements: Just as with Method 1, select all the elements you intend to mirror. This could be a few walls, furniture, or the entire layout of a room or even a "whole project" if all relevant elements are selected.
Activate Tool: Go to the Modify tab, Modify panel, and click on the Mirror (Draw Axis) icon (usually showing two triangles reflecting over a dashed line) or type the keyboard shortcut DM.
Draw Mirror Axis: Your cursor will change to a pencil icon. Click two points in the drawing area to define your custom mirror line. The orientation of this line determines the direction of the mirror. For instance, to mirror elements from right to left, you would draw a vertical line. If you draw a horizontal line, elements will reflect vertically (e.g., top-to-bottom).
Confirm Action: Once the second point is clicked, the selected elements will be mirrored across the line you just drew.

Important Considerations When Mirroring

Copy Option: By default, when you use either mirror tool, Revit creates a copy of the selected elements, leaving the original elements in place. If you wish to move (mirror without copying) the original elements, you must uncheck the "Copy" option in the Options Bar located below the Ribbon before defining your mirror axis.
Direction of Reflection: The chosen mirror line acts as the plane of symmetry. Any element on one side of the line will be reflected to the exact corresponding position on the opposite side. Understanding this relationship helps in correctly positioning your mirror axis to achieve the desired "right to left" or "top to bottom" reflection.
Datum Elements: When mirroring, especially an entire floor plan, pay attention to datum elements like grids and levels. If they are selected, they will also be mirrored. Mirrored grids might require renaming or adjustments depending on your project standards.
Constraints and Associations: Mirrored elements might retain or break existing constraints and associations with other model elements. Always review warnings and check the integrity of the mirrored geometry.
Linked Models: If your "floor plan" includes linked Revit models, you cannot directly mirror the contents of the link using these tools. You would typically need to open the linked model and mirror its contents there, or mirror the linked instance itself, which reflects its entire geometry.

By understanding these tools and considerations, you can efficiently mirror parts of or entire floor plans in your Revit projects, saving significant time in design development.