SketchUp is designed around flat faces and straight lines. That's not a flaw — it's what makes it so fast for most architectural work. But the moment a client wants a curved canopy, a flowing ramp, a barrel vault roof, or anything that bends through space, you hit a wall. The native Arc and Circle tools produce faceted approximations. Push/Pull extrudes them flat. Sandbox works for terrain but not for architectural surfaces. Curviloft — Fredo6's free extension — is the tool that fills this gap. This guide covers all three of its core tools, walks through a real-world canopy exercise, and shows you the mistakes that waste an hour before you even realize what went wrong.
SketchUp represents all geometry as triangles and quads — there are no true mathematical curves in the file format. When you draw an arc, SketchUp approximates it with line segments. When you push/pull that arc, you get a faceted cylinder, not a smooth one. More importantly, Push/Pull only works in one direction perpendicular to a face. It cannot follow a path through space, cannot connect two differently-shaped profiles, and cannot skin a frame of intersecting curves.
Best for: Recognizing the limits before you spend three hours fighting the wrong tool.
For rectilinear shapes, SketchUp's native toolkit is unbeatable. For anything that curves in more than one axis simultaneously — a saddle roof, a tensile membrane, a curved facade panel — you need a surface generation plugin. Curviloft is the most accessible and widely adopted option in the SketchUp ecosystem, and it has been maintained by Fredo6 (one of the most prolific SketchUp extension developers) for over a decade.
Curviloft does not work alone. It requires LibFredo6, a shared library that powers most of Fredo6's extensions. If you install Curviloft but skip LibFredo6, the menu entry appears but nothing happens when you click it — a confusing failure mode.
Open SketchUp → Extension Manager (Window menu on Windows, SketchUp menu on Mac).
Click "Install Extension" and install LibFredo6 first. Get it from SketchUcation or the SketchUp Extension Warehouse.
Install Curviloft from the same source. Both are free.
Quit SketchUp and relaunch. This step is not optional — the extensions will not initialize correctly until SketchUp restarts.
After relaunch, find Curviloft at: Tools → Fredo6 Collection → Curviloft.
Pro tip: If you already have other Fredo6 extensions (FredoScale, FredoCorner, JointPushPull), you likely already have LibFredo6. Check the Extension Manager's "Installed" list before downloading duplicates.
After installation, Curviloft adds a toolbar with three icons representing its three tools. You can also access them through the menu. Either way, understanding what each tool is for matters more than knowing where to click.
Loft by Spline is Curviloft's flagship tool. It generates a smooth surface that passes through two or more open or closed contours — profiles drawn at different positions or orientations in space.
Draw your first profile (e.g., a rectangle at one end of a curved corridor).
Draw your second profile (e.g., a circle or different rectangle at the other end).
Activate Loft by Spline. Click on the edges of each profile in sequence. A preview surface appears between them.
Press Enter to confirm. Curviloft generates the connecting skin.
The "spline" in the name refers to how Curviloft interpolates the surface between profiles — it uses a smooth mathematical curve rather than a linear interpolation, so the transition does not crease in the middle the way a simple ruled surface would.
Best for: Transitions between different cross-sections — a square column transitioning to a circular capital, a barrel vault connecting to a flat parapet, a curved corridor with varying width.
Watch out for: Profile orientation. If your two profiles are not consistently oriented, Curviloft will twist the surface. If the preview looks like a Möbius strip, undo, redraw one profile in the opposite winding direction, and try again.
You can loft through more than two profiles. Add a third or fourth intermediate profile to control how the surface bends along its length. This is how you model an S-curved roof beam or a twisting staircase soffit.
Where Loft by Spline connects profiles at arbitrary positions, Loft along Path takes a single profile and sweeps it along a defined path curve — similar to SketchUp's Follow Me tool, but with far more control over how the profile is oriented as it travels.
Draw your profile perpendicular to the intended direction of travel.
Draw the path: an arc, a series of connected line segments, or any open curve.
Activate Loft along Path. Select the profile, then the path.
Curviloft previews the swept surface. Options let you control whether the profile stays upright, rotates to follow the path tangent, or scales along the way.
Best for: Curved beams, arched window frames, helical staircases, swimming pool coping — any situation where you need a consistent cross-section to follow a non-straight path.
Watch out for: Very tight path curves relative to profile size. If the path radius is smaller than the profile width, the resulting surface will self-intersect. Increase the path radius or reduce the profile size before confirming.
A key difference from Follow Me: Loft along Path can scale the profile from one end to the other, producing a tapered swept surface — a common requirement for column pedestals, pergola beams that taper toward the eave, and structural fins.
Skinning fills an existing frame of edges with a smooth surface. The frame must consist of three or four sets of contiguous curves that form a closed boundary.
Build a 3D frame — four curved edges arranged to bound an opening in a facade, or the perimeter of a tensile canopy.
Activate Skinning. Click on each of the four boundary curves in order.
Curviloft fills the bounded region with a subdivided mesh that follows the curvature of the boundary edges.
Best for: Tensile membrane structures, curved glass panels with irregular boundaries, saddle roofs where all four edges are curves, organic forms like boat hulls or car body panels.
Watch out for: Boundaries that do not meet at corners. A gap as small as 0.01mm will block Skinning. Use Endpoint inference carefully, or weld the corners before skinning.
The resulting mesh from Skinning tends to be dense. After generating, select the surface and use Soften/Smooth Edges to adjust the visual smoothing without changing the geometry. For Lumion renders, this is usually enough. For BIM or fabrication export, reduce mesh density in Curviloft's options dialog before confirming.
This is the workflow most architects encounter Curviloft for the first time. A client wants a curved steel canopy — elliptical in plan, arching upward in the middle, resting on two end walls.
Draw the plan footprint: two parallel lines 6m apart, connected by elliptical arcs at each end.
Create the edge curves: draw the two long edges as arcs in elevation, rising 1.2m at the center from the wall attachment points to the crown.
Draw the end profiles: at each end wall, draw the cross-sectional profile matching the elliptical plan edge.
Activate Loft by Spline. Select the two end profiles. Check for twists in the preview surface.
Add intermediate profiles at the quarter-points of the span to guide surface curvature if needed.
Confirm and inspect. Orbit underneath and reverse any back-facing faces.
Make the canopy a component immediately — raw Curviloft surfaces stick to everything they touch.
Apply a metal material. The surface renders as a smooth shell in Lumion provided face normals are consistent.
Pro tip: Before sending to Lumion via LiveSync, purge unused materials and check the canopy component's face count in Entity Info. If it exceeds roughly 5,000 faces for a canopy this size, reduce Curviloft's segment count and regenerate.
The surface twists instead of flowing. Cause: profiles with inconsistent winding direction. Fix: undo, reverse one profile's winding direction, retry.
Curviloft says "no valid contours detected." Cause: the selected edges have a gap too small to see. Fix: check with the Measurements toolbar. A gap of 0.01mm will block Skinning. Snap endpoints carefully before running the tool.
The generated surface slows SketchUp. Cause: default segment count is too high. Fix: open Curviloft's parameter dialog before confirming and reduce segments per span to 6–8 for architectural use.
The surface doesn't meet the boundary curves. Cause: source edges in different groups or components. Fix: explode all source groups before running Curviloft, then immediately make the result a component.
Watch out for: Leaving Curviloft surfaces as raw geometry. Always wrap the result in a component immediately — hundreds of loose edges will merge with anything nearby.
Curviloft does not replace thinking about constructability. A canopy you model in 20 minutes might require significant rationalization before fabrication — curved glass panels need flat or single-curved geometry unless your budget includes cold-bent or frit-printed units. SketchUp will model anything; Curviloft will skin any frame. Whether that geometry is achievable in the real world is a separate question.
That said, for schematic design and client visualization, Curviloft is genuinely invaluable. It lets you explore form options that would take hours with native tools, present them in Lumion with realistic materials and lighting, and iterate quickly based on feedback. The three core tools — Loft by Spline, Loft along Path, and Skinning — cover the majority of curved-surface situations that arise in architectural practice.
Install it, restart SketchUp, and give yourself 30 minutes with a test model before you need it for a real project. The time-pressure situation is not the moment to learn that your profiles are wound the wrong way.
If you have been accepting flat approximations where your design calls for something more, Curviloft is the plugin that removes that constraint. Install LibFredo6 and Curviloft, learn the distinction between the three tools, and run through the canopy exercise above with a simple test model. Once the muscle memory is there, organic surfaces become a one-hour modeling session rather than a two-day workaround.
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