Technology: A BIM experience from the building finishes sector

John Butler of specialist contractor London Drywall sets out the status quo of Building Information Modelling (BIM) in the building finishes sector,  highlighting useful insights and notes of caution.

We often joke that the BIM experience can be compared to assembling flat-pack furniture without instructions: once you’ve sussed it out and built a few items of furniture correctly at the third or fourth attempt, it does eventually become easier!

There is still a common fallacy with company owners, directors and senior managers that BIM is purely a 3D design requirement and a  marketing badge to be promoted. In reality, it is more like this: the trade contractor’s designers have been left to write an O&M manual  populated with a full NBS specification for each design element at the outset of the design  process, combined with a fully managed,  accurate and developed 3D design on top.

Overall project costs related to BIM design are likely to be significantly higher than those for traditional 2D design, with multiples of 5 to 10 times normal costings being typical according to the level of detail required. Clients and financial managers don’t always expect to pay for the  level of the trade contractor’s resourcing required, and obtaining sufficient financial allowances in competitive tender aren’t always possible, putting additional pressure on trade contractors’ margins.

The industry-leading software, Autodesk’s Revit, is complex to learn and understand and doesn’t automatically link with other BIM software used in sectors such as M&E, where Autodesk’s CADduct, AutoCAD MEP and Navisworks are often used. These operate on a different level with very limited integration capability, especially for the much-heralded clash-detection capability.

To invest in the equipment,  training and staff engagement  required for in-house capability, you’re talking hundreds of  thousands – not tens of thousands – of pounds. And the timescale for full implementation from an existing in-house AutoCAD / Sketchup design capability to full 3D BIM provision has to be measured in years, not months.

Attendance by a trade contractor’s  competent BIM-savvy design manager is pretty much required at weekly design meetings over the life of the pre-construction and construction period, and not just in the early days that would be typical of traditional 2D design input.

The decision to outsource to an outside freelance BIM design agency is not  straightforward, incredibly expensive  (costing £1,000s per week) and only allows your company to gain, not manage or learn from, the knowledge process required for, and benefits deriving from, BIM.

Whether BIM design is outsourced or not, trade contractor’s in-house design management and reporting systems require an increased level of sophistication. There’s no obvious source of qualified, competent staff that can be brought in to a typical trade contractor’s design  department, and many graduate qualified designers and part-qualified architects with 3D / BIM capability don’t automatically consider trade contractors as their career choice, leaving the finishes sector as the lowest level in their career pecking order.

Issues with clients’ BIM managers and principal designers

Live BIM models used in commercial office  fit-out often suffer inaccuracies because  base-build models have been used without  as-built ‘cloud survey’ verification later on, which leads to the actual on-site building dimensions being different from the initial model developed at ‘shell and core’ stage. Revised solutions and modifications are then required at the critical construction stage.

Lead architects are not  always familiar with BIM  software, leaving this element to BIM technicians in their office, and their design details are often  developed in 2D CAD, not  necessarily then being developed into a 3D model to check they work  in practice.

Differing applied finishes such as wall tiling and skirting affect overall wall thicknesses, but need to be added as separate BIM layers, not  incorporated into the wall make-up. For example, door frame thicknesses and junction alignment where finishes are local rather than continuous and where wall type specifications vary.

Design management philosophy

M&E trades were the early BIM adopters – they’d been designing in 3D for a long time – followed by trade contractors with their own designed system-heavy components such as glazed partitioning.

Drywall manufacturers have been slow in  providing any system-usable BIM information other than LOD 200 wall type family make-ups with their own specification written into them, essentially approaching BIM from only a  marketing and branding exercise. For projects at LOD 400 and LOD 500, they’ve still not created full 3D model components for accurate detailing, so drywall contractors have had to create their own 3D components with no manufacturer verification of authenticity or accuracy.

Practical implementation

The BIM model is never static; it requires  constant monitoring for daily changes.

It’s the trade contractor’s responsibility to update their models in line with the constantly changing BIM manager’s local area model and master BIM model, and then to feed that updated information back to the client’s BIM manager on a weekly basis, while maintaining a full audit trail.

Delays in updating the master model with small changes are inevitable as solutions are often still worked out by hand sketches. Some other trade contractors only provide  indicative details due to their late  appointment, such as joinery, furniture and  AV, which impacts coordination of backing plywood locations within walls, door opening sizes and schedules.

BIM-related issues

Be careful of agreeing to offer BIM to any level of detail above LOD 300 as the complexity of information required to be produced is currently what I deem to be beyond the capability of  drywall contractors at this stage without  excessive costs being incurred.

Backwards saving of BIM models from Revit version 2016 to, say, Revit version 2014 is not possible, and if the master model is being maintained in Revit 2014 this poses issues with any model loaded as it requires a licensed version of Revit 2014 (and its functionality) to be maintained for that project, while other projects might be standardised on a later version, say Revit 2015, which is incompatible.

Despite the effort to fully populate the BIM model with all the specification information, this has so far not reduced the requirement to provide comprehensive hard copy and  electronic format O&M manuals, creating  duplication of effort.

Benefits of BIM

As the design and construction progresses and built drawings and models are developed, the likely costs to produce that information at a later stage reduce. And once the information is loaded into the BIM model, standardisation and automation of design activities such as wall tagging, quantification, and eventually costing will be much faster.

Provision of Revit and IFC models can substantially improve the dependability of information issued to manufacturers of off-site components and systems, for example for LGSF structural drywall panels.

BIM – the future

As alluded to in my opening analogy, the more exposure you have to BIM and its requirements, the more familiar and easy to understand it all becomes. As a sector, we’re getting there, but there are still issues to be aware of and challenges to overcome.

What do you think?

FIS would like to hear your thoughts on BIM. Email info@thefis.org