Fibre Reinforced Facade Encyclopedia: Design and detailing
Parametric design is a method in which geometry is defined by rules and variables instead of being drawn directly, so that changing an input regenerates the model and everything derived from it. On a facade it is the workflow that converts a surface into panels, joints, fixings, setting out points and fabrication data, and it is what makes an envelope of several thousand non-repeating panels documentable at all.
A facade of 1,800 unique panels drawn by hand is 1,800 drawings. Defined parametrically it is one definition, one panel schedule and 1,800 automatically generated sheets, and a 50 mm change to the panel module becomes a re-run rather than a redraw.
At a glance
| Property | Typical value | Note |
|---|---|---|
| Common tools | Grasshopper for Rhino, Dynamo for Revit | Also Houdini and Generative Components |
| Primary output | Panel schedule, per-panel geometry, setting out coordinates | Feeds shop drawings and CNC formwork |
| Typical panel count | 200 to 5,000 panels per facade | Sculptural envelopes sit at the upper end |
| Mould reuse target | 5 to 20 pulls per mould | The single largest cost lever on a moulded facade |
| Geometry tolerance in model | plus or minus 1 to 3 mm | The model must be tighter than the fabrication tolerance |
| Geometry exchange | IGES, STEP, DXF, DWG, IFC | Format, units and origin agreed with the fabricator first |
| Option turnaround | Minutes per option once the definition is stable | Compared with days for a redrawn option |
| Panel weight feedback | 5 to 50 kg/m² depending on material | Drives crane class and bracket design directly |
What parametric actually means
A parametric model is a chain of dependencies. A base surface drives a subdivision, the subdivision drives panel outlines, the outlines drive joint centrelines, the joint centrelines drive fixing positions, and the fixing positions drive bracket schedules. Nothing in that chain is drawn twice. When the base surface moves, every downstream item updates, which is the whole point, and which is also the whole risk: an error near the top of the chain propagates into every panel without announcing itself.
It is not the same as building information modelling. A parametric definition generates geometry and data; a BIM model holds and coordinates them. Most facade teams use both, driving the geometry in Grasshopper or Dynamo and pushing the resolved panels into a federated model. See bim for what the model has to carry once the geometry is settled.
The facade workflow
- Surface definition: a clean, continuous NURBS surface, usually simplified from the architect’s concept model and agreed as the single geometric source.
- Panelisation: dividing the surface into panels using a quad grid, a triangulation, a strip pattern or a developable strip family.
- Rationalisation: reducing the number of genuinely unique panels, and flattening panels that are nearly planar.
- Joint and fixing logic: joint widths applied as offsets, fixing points placed by rule, bracket adjustment ranges checked against tolerance.
- Panel data: an ID, area, mass, curvature type, mould family, finish and lift sequence for every panel.
- Fabrication output: per-panel surfaces, mould geometry, setting out points and drawing sheets generated automatically.
The order matters. Panelising before the surface is agreed is the most common cause of rework, because a small change to the base geometry can change every panel outline and therefore every mould.
Rationalisation is where the money is
The cost of a moulded facade panel is roughly the cost of the mould divided by the number of pulls from it, plus the cost of the pull. Every extra reuse spreads a fixed cost further, so the job of the parametric definition is not to make interesting geometry but to find the repetitions inside interesting geometry. Grouping panels into families, snapping near-identical panels onto a common master, and accepting a slightly larger joint variation are all trades that can halve a mould count.
Practical levers include restricting the surface to developable strips, using planar quadrilateral meshes where the geometry allows, converting free curves to circular arcs of a limited radius set, and allowing a mould to be adjusted by inserts between pulls. See double curvature for the geometric reasons some of these work and some do not.
What the fabricator needs from the model
Fabrication does not consume a parametric definition. It consumes resolved geometry and a schedule. A fabricator needs a clean solid or surface per panel in an agreed format, a single project origin and orientation, units stated explicitly, and a panel numbering system that will survive being written on a crate in a shipping yard. Revit family geometry is rarely sufficient for a curved panel; NURBS surfaces exported as IGES or STEP usually are.
Limits and failure modes
A parametric definition is only as good as its assumptions, and it fails quietly. Tolerance is the usual omission: a definition built on the theoretical structural grid will produce panels that do not fit a frame built to plus or minus 20 mm, because the model was never given the survey. Authorship is the second: a definition that only one person can open is a project risk, so name the definition owner in the execution plan and keep the file readable.
The third failure is treating the model as a licence for unlimited variation. Every unique panel carries a mould, a drawing, a lift and an inspection. Variation that no one can see from the street is cost with no return, and the discipline of parametric work is deciding where the variation is worth paying for.
Standards and references
- ISO 19650-1 and ISO 19650-2 Organization and digitization of information about buildings, including information management using BIM
- ISO 16739-1 Industry Foundation Classes (IFC4) for model exchange
- ISO 10303 (STEP) and IGES for exchange of NURBS surface geometry
- NATSPEC National BIM Guide and NATSPEC BIM Reference Schedule
- GRCA Practical Design Guide for GRC (panel geometry and mould provisions)
- AS/NZS 1170.2 Structural design actions: wind actions, including wind tunnel testing for complex geometry
- AS 3610 Formwork for concrete, for mould surface classes derived from the model
Where this matters on a ShapeShift project
Spanda: A sculptural public artwork where the geometry was resolved as a rule-driven model before any mould was cut.
Related terms
Questions specifiers ask
Is parametric design the same as BIM?
No. A parametric definition generates geometry and data from rules; a BIM model holds, coordinates and hands over that information. Facade teams normally run both, driving geometry in Grasshopper or Dynamo and pushing resolved panels into the federated model.
Why does parametric design suit moulded composites?
Because the cost of a moulded panel is dominated by the mould, and a parametric model is the only practical way to count, group and minimise unique moulds across thousands of panels while keeping the architectural intent.
What software is used?
Grasshopper for Rhino and Dynamo for Revit are the two in general use on facade projects. Houdini and Generative Components appear on larger jobs. The tool matters far less than the discipline of the definition.
When should the geometry be frozen?
Before mould cutting. Mould making dominates the fabrication lead time, so a change to the base surface after moulds are released is a restart of the most expensive part of the package, not an amendment.
Does the fabricator work from the parametric model?
No. Fabrication uses resolved per-panel geometry in an agreed exchange format with a single project origin, stated units and a fixed panel numbering system. Agree all four before the definition is written.
Working up a rule-driven facade and want early advice on panelisation and mould reuse? We work from the geometry, not from a finished drawing set. Talk to our engineering team
Reviewed by Richard Halvorsen, General Manager, ShapeShift Technologies. Last updated September 2026.