Comprehensive Guide to Creating Roofs by Extrusion in Revit

Creating roofs in Revit using the extrusion method offers architects and designers greater flexibility for unique architectural designs. This article explores the process of modeling roofs by extrusion in Revit, explaining its significance, step-by-step guidance, and best practices to optimize your workflow. Understanding this technique is crucial for professionals who need to customize roof shapes beyond standard options within Revit.

What Is Roof by Extrusion in Revit?

Revit offers multiple methods for roof creation, one being roof by extrusion. Unlike footprint roofs that rely on planar boundaries drawn on levels, extrusion roofs are generated by sweeping a profile along a path. This method is ideal when designers need to create non-rectangular, sloped, or curved roof shapes that do not easily conform to standard roof forms.

The extrusion technique allows complete control of both the roofing profile and the path it follows, enabling intricate roof designs typical in contemporary architecture. Because the profile is sketched separately from the path, this method offers high customization for complex residential, commercial, or institutional projects.

Advantages of Using Roof by Extrusion

• Flexibility in Design: Enables creation of custom roof cross-sections for distinctive architectural styles.
• Precision Control: Both profile shape and extrusion path can be precisely adjusted to meet design specifications.
• Adaptable Geometry: Useful for modeling curved, sloped, or non-standard roof forms that footprint roofs cannot achieve.
• Integration with Other Elements: Allows joining complex roofs with curtain walls, facades, or structural components seamlessly.
• Parametric Modifications: Profile and path changes automatically update the roof geometry, enhancing design iteration efficiency.

Step-by-Step Guide to Creating a Roof by Extrusion

1. Set Up Reference Planes and Levels

Start by creating appropriate reference planes or levels to guide the extrusion path. This ensures the roof extrusion is positioned accurately in the 3D model. It is common practice to align these with existing building grids or elevations.

2. Access Roof by Extrusion Tool

Navigate to Architecture > Roof > Roof by Extrusion. Select the desired work plane (typically a vertical or sloped reference plane) on which you will sketch the profile.

3. Sketch the Roof Profile

Draw the 2D profile shape of the roof cross-section. This profile represents what the roof will look like in a cut through the extrusion. Precision in this step is essential—include slopes, thickness, and any architectural details needed.

4. Define the Extrusion Path

After finishing the profile, select the extrusion path which will dictate the shape and direction in 3D. You can create straight or curved paths using existing reference planes or model lines in Revit. Adjust the length and slope to customize the roof accordingly.

5. Adjust Roof Parameters

Once the extrusion is generated, fine-tune parameters such as offsets, materials, and joins. Use the roof properties panel to change these attributes and control the roof’s physical appearance and behavior.

6. Validate and Integrate the Roof

Inspect the roof in 3D views and section views to confirm accuracy. Integrate with walls and other components by using join tools or modifying walls to accept the new roof geometry for a seamless model.

Practical Tips for Effective Roof Extrusion Modeling

• Use Reference Planes Extensively: Maintain clarity and control by drawing your extrusion path on explicit reference planes.
• Keep Profiles Simple: Overly complicated profiles can slow model performance; opt for simplified yet representative shapes.
• Employ Work Plane Management: Assign profiles and paths to appropriate work planes to avoid confusion and errors.
• Regularly Check Intersections: Roofs by extrusion can intersect walls and other elements awkwardly without proper joining.
• Utilize Preview Mode: Preview the extrusion as you develop it to catch mistakes early on.

Common Challenges When Using Roof by Extrusion and How to Overcome Them

Misaligned Profiles and Paths

One frequent issue is extrusion profiles not aligning correctly with paths, causing unexpected roof shapes. To prevent this, carefully place both profile and path on coordinated planes and use snapping features.

Performance Slowdowns

Complex extrusions can impact Revit’s performance. Minimize profile complexity, and avoid excessive use of high-resolution curves.

Visibility and Display Issues

Sometimes roof extrusions don’t display properly in views. Ensure correct view range settings and that the extrusion elements are not inadvertently hidden or filtered.

Joining Problems with Other Elements

To fix gaps or overlaps where roofs meet walls or other roofs, use Revit’s join geometry tools and manually adjust elements to enhance model precision.

Advanced Techniques with Roof by Extrusion

Creating Curved or Sinuous Roofs

By defining curved extrusion paths using splines or arcs, designers can generate smooth, flowing roof forms that enhance contemporary architectural aesthetics.

Combining Multiple Extrusions

Complex roofs can be built by combining several roof extrusions with different profiles or paths, allowing segmented yet harmonized roof systems.

Using Family Roofs by Extrusion

For even more flexibility, roof extrusions can be embedded within families, giving parametric control over roof shape in project templates or repeated elements.

Comparison: Roof by Extrusion versus Roof by Footprint