Create Automatic Roofs in FreeCAD Arch

Generating a roof automatically in FreeCAD requires using the parametric Roof tool found in the BIM or Arch Workbench. By defining a closed base outline using a Draft wire or existing wall faces, FreeCAD can instantly calculate and generate standard roof geometry, such as hip or gable designs. This guide outlines the exact steps to create the base outline, generate the roof structure, and customize key parameters like slope angles, thickness, and overhangs.

Step 1: Switch to the BIM or Arch Workbench

  1. Open your model in FreeCAD.
  2. In the workbench dropdown menu, select BIM (or Arch in older FreeCAD versions).

Step 2: Create a Base Profile

The Roof tool requires a closed 2D shape (a planar face or closed wire) to determine the perimeter and layout of the roof:

  1. Switch to the top view (press 2 on the numeric keypad).
  2. Using the Draft Wire tool, draw a closed polygon representing the outer boundary of your building or walls. Ensure the wire is completely closed (press Close or snap to the first point).
  3. Alternatively, if you already have 3D walls, select the top horizontal face of the wall assembly.

Step 3: Run the Roof Generator

  1. In the tree view or 3D viewport, select the closed Draft wire or top wall face.
  2. Click the Roof tool icon in the toolbar (or navigate to 3D/BIM > Roof from the top menu).
  3. FreeCAD will automatically generate a default hip roof matching the shape of the selected footprint.

Step 4: Adjust Global Dimensions

To modify the overall geometry of the generated roof:

  1. Select the new Roof object in the Tree view.
  2. Go to the Property panel on the lower-left and select the Data tab.
  3. Edit the following basic properties:
    • Thickness: Sets the depth of the roof slab.
    • Overhang: Extends the roof eaves beyond the base wire perimeter.
    • Height: Adjusts the default elevation of the roof ridge.

Step 5: Customize Roof Profiles (Hip to Gable)

By default, FreeCAD creates a hip roof where all sides slope inward. To change specific sides to a vertical gable:

  1. Select the Roof object in the Tree view.
  2. In the Data tab, locate the Angles list property. This list contains an entry for each edge of your base polygon (e.g., [45.0, 45.0, 45.0, 45.0]).
  3. Click the ellipsis (...) next to Angles.
  4. Change the angle of the desired end faces from 45.0 to 90.0. A 90-degree angle creates a vertical gable wall instead of a sloped facet.
  5. Click OK to update the model.

Step 6: Generate Internal Structural Framing (Optional)

If you require a timber or steel rafter framework rather than a solid roof volume:

  1. Select the individual faces of your generated roof.
  2. Use the BIM Structure or Arch Frame tool to array framing elements across the roof planes.
  3. In the Property view of the frame, set the structural profile (e.g., standard lumber or I-beam) to build rafters automatically beneath the roof shell.