After the contract, arguably the most important document on a project is now the BEP (BIM Execution Plan) setting out who does what, when and how throughout the project across all parties.

What does ‘specific’ actually mean ? For many UK building contracts for building services the contractor must meet the performance characteristics set out in the specification and data. He is entitled to choose any piece of plant or equipment so long as it meets the performance and the space. Is that specific ? As a designer specifying, I believe the data is specific, but the geometry, the piece of plant and therefore the actual object in the model, is generic. Should that be LOD 200 or 300? Many are the debates that we’ve had in the office and with our collaborators.

Can we address this without reinventing LOD, perhaps with a dual way to specify? Should we be stating an LOD for data and a separate LOD for geometry? This would better define what can be relied upon, and would enable BEPs to show progression in model development between RIBA stages 2 and 3 for any systems where the Contractor makes the final choice, such as facades. Eg Stage 2: LOD 200 for geometry and data. Stage 3: LOD 200 for geometry, but LOD 300 for data, clarifying the performance characteristics are now specific but the actual item not chosen.

There are many guides on LOD; the one most often referred to is from BIMForum, giving examples for separate elements. However this further confuses by bringing in LOD 350; not everybody agrees with its introduction or some of the system descriptions for different LODs. A quick search of the internet will give you many alternative guides and webpages dedicated to guiding you through the levels of LOD, but these are still only others’ interpretations.

I for one think we should stick to just the 5 definitions, but separate out the data from the geometry. The digital plan of work for PAS 1192 is under development but is not due to be completed until mid 2015. Will this pick up data and geometry as separate entities? Time will tell. Until then, we all need to be clear of our specifics, so we’re not committing to model more than we bargained for.

Kate Fletcher, Arup Associates                                                                                                                                                        Kate is an Associate and leads the Public Health team in Arup Associates. She has led the Public Health teams on wide range of projects that include a LEED Platinum Data Centre in Qatar, King Abdullah Sports City in Saudi Arabia and the multi-award winning Engineering and Computing Building at Coventry University. She has worked in London, Manchester and Mauritius offices for Arup before joining Arup Associates.She is an engineer at the heart of integrated design, pioneering virtual design at Arup Associates. She plays a key role in the leadership of BIM in the practice and BIM implementation across the UK in the wider Arup Group.Kate believes in challenging convention, seeking out new and alternative ways to design to create beautiful, efficient and sustainable buildings with a key emphasis on sustainable water strategies. She is a fellow of CIBSE and a LEED AP.