Case Study – Cladding Subcontractor BIM

We recently completed the Innovation Centre at Infinity Park in Derby, with Main Contractor GF Tomlinson. Built for Derby City Council and been christened the ‘iHub’, the building will open this summer. It was a Level 2 BIM project with the main ‘Tier 2’ subcontractors required to model their packages for federation with the ‘Tier 1’ models. This case study looks at how Varla (UK) modelled the complex cladding and roofing package.

The iHub Derby. Cladding curves on plan and elevation

The building is curved on plan as well as on elevation, which meant this was going to be a challenge even for an experienced modelling team. Varla turned to Jon Sheridan of e-DNA who they’d worked with previously on Zaha Hadid’s Glasgow Transport Museum.

Varla previously worked with Zaha Hadid

Jon had a lot of experience modelling for cladding fabrication using Rhino with Grasshopper, but modelling as part of the BIM process was new. The first question the design team had to answer was what format could we all work with – the obvious answer was IFC. The great thing about IFC is that it can be federated not just in review software (e.g. Navisworks or BIMsight), but can also be loaded into authoring packages such as Revit, which the design team were using.

The Varla subcontract package had a number of elements that all needed to be modelled:

  • Insulated carrier panels (used instead of an SFS system)
  • Rainscreen support system (Lingrid)
  • Aluminium Rainscreen cladding
  • Stainless steel shingle cladding
  • Topdeck roofing system

Jon modelled each of these elements separately in Rhino and provided separate IFCs to the design team. The model was further split between areas of the building. This meant the large model size could be broken up into discrete chunks which could be loaded, and more crucially unloaded, separately.

The IFC models were provided to the design team in discrete chunks

To generate the geometry in Rhino, Jon used the Grasshopper visual scripting package. This allows you to great scripted definitions of the desired geometry which are then generated in Rhino. Parameters such as cladding module, depth, profile and 3 dimensional paths can all be defined within the script, and can be iterated as required. Dynamo for Revit works in a similar way, but Jon believes the nurbs features of Rhino are superior for this type of work.

Grasshopper for Rhino is a lot like Dynamo for Revit – visual scripting
Cladding modelled in Rhino with Grasshopper and exported to IFC

To then turn Rhino models into IFC for the design team, Jon used plug-ins available from Geometry Gym, a blog/company run by John Mirtschin. ‘GG’ can turn the Rhino geometry into a series of lightweight extrusions in IFC format, and also supports data added to the geometry.


Once the design team received the IFC cladding models, our preferred federation approach was to link the IFC files directly into Revit. Our process is more one of coordination than clash detection, and the automated clash tools of applications like Navisworks can be more of a hindrance than a help. Using the hundreds of saved views, sections, and section boxes already set up in Revit, we were able to check for alignment, clashes, errors and comment on module arrangement options very easily.

The size of the subcontract models means they couldn’t all be loaded at the same time, with current computing power, but this was a valuable exercise in getting subcontract design models into the BIM workflow processes.

You can find more example of Jon’s work in BIM, industrial design, automotive design and even yacht design, over at his website

The Employer’s Agent and Project Manager was Turner & Townsend
The client-side architect and author of the EIRs was Bond Bryan Architects

Franklin Ellis Architects, 2016



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The BIM guys at Franklin Ellis Architects

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