How to Create a Corner Mullion in Revit
Seven steps in Revit, or one sentence in Mira.
Do it with MiraDelete the two mullions where the curtain walls meet, click Architecture tab › Build panel › Mullion and pick an L, V, Trapezoid or Quad corner type. Click the corner grid line to place it. For your own size, duplicate a type.
Or, just ask Mira, a free add-in, to list the curtain wall corners still missing one.
How to do it in Revit
Step 1: Choose the corner shape
Revit has four corner mullion types. With L, the panels meet the ends of the two legs, and with V, their sides; a Trapezoid has a center width, and a Quad two depths that make a square, a rectangle or a kite (Autodesk Help: About Corner Mullion Types).
Step 2: Make a type at your size
Select a corner mullion, or start the Mullion tool and pick one, then click Edit Type in the Properties palette, click Duplicate and name the type for its size. For L and V types, set Leg 1, Leg 2 and Thickness; for a Quad, Depth 1 and Depth 2 (Autodesk Help: Mullion Type Properties: L and V Corners).
Step 3: Clear the corner
In a 3D or plan view, select the mullions at the two wall ends that meet and delete them. Mullions that come from the curtain wall's type can be pinned, so unpin them first.
Step 4: Place the corner mullion
Click Architecture tab › Build panel › Mullion and pick your corner type in the Type Selector. On the Modify | Place Mullion tab, choose Grid Line to run the full height, then click the grid line at the corner (Autodesk Help: Place a Mullion on a Curtain Grid).
Step 5: Check it in plan
Look at the corner in a plan view at Fine detail. If the mullion sits off the glass line, change Offset in its type: a corner mullion's offset is measured relative to the panels.
Step 6: Swap a corner later
To change one corner, select its mullion and pick another corner type in the Type Selector. A change in Edit Type changes every corner of that type in the project.
Step 7: Use a profile for any other shape
Corner types can't take a profile, because Profile isn't available for corner mullions. For a shape none of the four can make, build a mullion profile family, set it as Profile under Construction in a rectangular mullion type, and place that type on the border grid line at the end of one wall (Autodesk Help: About Mullion Profiles).
What to watch for
Corner mullions are system types. They're part of Revit's system mullion family, not .rfa files, so you can't load one from a folder. New ones come from duplicating a type, the same way as wall types, and keeping them in your template gives every project the same ones.
Some settings skip corners. Angle, Position and Profile aren't available for corner mullions, so their shape comes only from the leg, depth and thickness values.
Horizontal mullions miter on their own. When two curtain walls with horizontal mullions join, Revit miters those mullions at the join, so only the vertical corner needs a corner mullion.
Profiles can have holes. Since Revit 2025, mullion profiles can have more than one loop, such as a hollow tube section. To build the profile family itself, start from how to create a family.
Corner types drift between projects. Each project ends up with its own L corner at slightly different leg sizes, and a corner missed on one elevation shows up only in a rendering or a review. Keeping the curtain wall and mullion types your firm builds with in the template, as firm standards, means each project starts with the right corner.
Or, just ask Mira to do it.
Mira is an AI thinking partner for Revit that automates the work you repeat and builds tools your team needs.
- Type this in Mira
List the curtain wall corners in this model that don't have a corner mullion yet.
Mira only reads the model for this one. It lists each place where two curtain walls meet without a corner mullion, with the level and what sits there now, and changes nothing. It may write a small tool to find the corners, which asks Allow first.
How do I add a corner mullion in Revit?
What are the corner mullion types in Revit?
How do I make a custom corner mullion in Revit?
Why can't I change the profile of a corner mullion?
Can I load a corner mullion family in Revit?
Related Revit how-tos
- How to Create a Family in RevitClick File tab › New › Family, pick a template such as Generic Model, and set Family Category and Parameters. Draw reference planes, label their dimensions as parameters, lock geometry to them, add sizes in Family Types, then save and Load into Project. Or, just describe a simple family and Mira builds it and places it in your model.
- How to Create and Change Wall Types in RevitSelect a wall, click Edit Type, then Duplicate, and name the new type. Click Edit next to Structure to set each layer's function, material and thickness. To change walls to the new type, select them and pick it in the Type Selector. Or, just ask Mira, a free add-in, to swap every wall of one type to another on a level.
- How to Edit a Family in RevitSelect a placed instance and click Edit Family, or right-click the family in the Project Browser and choose Edit. Make the change, then click Load into Project and choose whether to overwrite the existing version. Or, just ask Mira, a free add-in, to make a size change and say if it needs the Family Editor.
- How to Load a Family in RevitClick Insert tab › Load from Library panel › Load Family, browse to the .rfa file and click Open. Select several files to load them together. To update a family that's already in the project, right-click it in the Project Browser and choose Reload. Or, just ask Mira, a free add-in, to load the families in a folder you pick.
- How to Use Formulas in Revit Family ParametersIn the Family Editor, click Create tab › Properties panel › Family Types. In the Formula column next to a parameter, type an expression with exact parameter names, such as Width + 2". Click Apply to check. Formulas take arithmetic, if(), rounding and trig. Or, just ask Mira, a free add-in, to set formulas on parameters the family already has.
- How to Create and Use Type Catalogs in RevitA type catalog is a .txt file with the same name and folder as the family's .rfa. Its first row declares parameters as Name##type##units; each row after it is a type. On load, Revit lists the types so you pick only the ones you need. Or, just ask Mira, a free add-in, to add a type to a catalog.
Try it yourself.
Or bring it to the firm.
The download is free and takes a minute. The firm conversation is where your standards, your library, and your rollout get built. Start wherever makes sense.