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What is BIM and why do we use it for retrofit projects?

Updated: Nov 30, 2023

At Holt Architecture we've long been fervent advocates of the use of Building Information Modelling (BIM) and were among some of the earliest SME adopters in the UK.

Whilst BIM is often considered more suitable for large-scale and new-build projects we made an early decision to use BIM on all our projects. It's been challenging at times, but we have also seen great dividends, both in terms of the quality of our design and the accuracy of our work.

So, what exactly is it and why do we use BIM for retrofit projects?


What is BIM?

BIM, or Building Information Modelling, is a 3D digital representation of a building's physical and functional characteristics, providing a collaborative platform for architects, engineers, and construction professionals to plan, design, construct, and manage buildings more efficiently.

What’s the difference between BIM and CAD?

Most people are familiar with Computer Aided Design (CAD) as it is so universally adopted in the design and construction industry. BIM and CAD are both computer-based methods of creating and managing designs for construction projects,however, they have some key differences that make them suitable for different purposes and applications. Here are some of the main differences between BIM and CAD:

  • BIM stands for Building Information Modelling, while CAD stands for Computer-Aided Design.

  • BIM is a process of creating and managing information on a construction project across the project lifecycle, while CAD is mainly a tool for creating drawings and models of a design.

  • BIM models contain information about all the different components represented in a design, such as materials, equipment, dimensions, performance, and cost, while CAD models are mostly geometric representations of the design without much data attached.

  • BIM models are parametric, meaning that information can automatically update when changes are made to any part of the design, while CAD models are static, meaning that they must be manually modified when changes occur.

  • BIM models are 3D by default, while CAD models can be either 2D or 3D.

  • BIM enables better collaboration and communication among different stakeholders involved in a project, such as architects, engineers, contractors, and owners, while CAD is more of an individual design tool.

  • BIM allows for better analysis and simulation of the design, such as energy efficiency, structural integrity, cost and sustainability, while CAD is more focused on the visual aspects of the design.

6 Key Benefits of BIM

BIM has many benefits for the construction industry, such as:

  • Maximised efficiency: BIM enables consistency and optimises time management and strategic decision-making throughout the lifecycle of a building or infrastructure

  • Reduced costs and wastage: When used by competent professionals,BIM software helps to avoid errors, clashes, and rework, which can save money and resources.

  • Improved quality and performance: BIM allows for better designanalysis and simulation of the project, which can enhance the functionality, sustainability, and safety of the design.

  • Enhanced collaboration and communication: BIM facilitates the sharing and integration of information among different stakeholders, such as architects, engineers, contractors, and owners.

  • Increased innovation and competitiveness: BIM enables the use of advanced technologies, such as parametric design, virtual reality, and artificial intelligence, which can create new opportunities and challenges for the construction industry.

Why Isn't BIM Used on All Construction Projects?

There are various reasons:

  • Lack of awareness and understanding: Many construction professionals don't understand BIM and its potential advantages, or have misconceptions about its complexity and cost. They also don't have the skills and training to use BIM effectively.

  • Resistance to change and innovation: Many construction professionals are reluctant to change their traditional ways of working and adopt new technologies and methods.

  • Fragmentation and silos: The UK construction industry is characterised by a fragmented and adversarial culture, where different parties involved in a project work in isolation and have conflicting interests. This hinders the collaboration and integration required for BIM to succeed.

  • Lack of standards and guidance: The UK construction industry initially lacked a clear and consistent framework for BIM adoption, such as standards, protocols, specifications, and best practices. This created confusion and inconsistency among different stakeholders and projects.

How widely is BIM used in the UK?

The UK is now considered somewhat of a global leader in the adoption of BIM technology. As of 2020, about 73% of all construction industry professionals admitted to being aware of and using BIM on projects, while 26% were aware of its existence alone, and a lone 1% were neither aware nor using BIM.

However, this is mostly limited to larger projects or those that are publicly procured. There is still a lag in uptake both on smaller projects and where projects involve working with existing buildings, which is where Holt Architecture differ.

So, why do we use BIM for retrofit and urban surgery projects?

Working with existing buildings and structures presents its own set of challenges but a ‘demolition and new build’ only approach is not feasible if we are to work toward net zero and other sustainability goals. We believe that the use of BIM is well suited for retrofit projects because it allows for accurate documentation of existing structures, enables clash detection to identify conflicts with new elements, facilitates precise planning and coordination of modifications, and streamlines the communication and collaboration among various stakeholders, ultimately improving efficiency and reducing errors in the retrofit process.

Z height coloured image of a point cloud analysing levels of  roof
Analysis of a point cloud to assess heights of an existing roof to inform setting out of new steel structure and coordinate services

Coloured image of a point cloud mapping out existing building services
Mapping out existing services on a point cloud

A few key examples are listed below but if you’d like further information on how we work, please contact us for a chat.

  • Inadequate Documentation:

Older buildings often lack accurate and comprehensive as-built drawings or documentation, making it challenging to understand their original construction and systems. The use of point cloud surveys and resulting 3D models provides a far greater level of information than traditional 2D surveys. This provides many benefits including the ability to define strip out and select demolition works in greater detail, measure historic building features accurately and spot potential issues such as floors being out of level. The as-built BIM model can then be used as a historical record, making it easier to plan future renovations or maintenance.

  • Historic Preservation:

When dealing with historically significant buildings, preserving the architectural integrity and historical value while incorporating modern amenities can be a delicate balance. In addition to the creation of enhanced surveys, BIM facilitates consultants and engineers to coordinate more precisely, meaning that compromised design changes arising from site conditions which could threaten historic fabric are reduced.

  • Space Constraints:

Existing layouts and structural elements may limit the flexibility of interior spaces and require innovative design solutions. BIM can be used to undertake rapid optioneering, looking at multiple ways of maximising floor area, space planning offices or layouts of flats. Work in progress surveys and as-built clash detection with BIM models allows us to identify any deviations from the design which if left unremedied could impact head heights or useable space.

  • Energy Efficiency:

BIM can simulate energy performance, allowing for the optimisation of retrofit options to improve sustainability and reduce operational costs. Working with energy consultants it’s possible to use the BIM model to calculate embodied and operational carbon usage, and together with optioneering find sustainable alternatives.


Overall, BIM enhances efficiency, reduces risks, and improves the outcomes of retrofit and urban surgery projects by providing a comprehensive digital platform for design, analysis, and documentation.In essence, BIMisn't just a tool; it's a transformative approach that empowers us to revolutionise urban spaces. As pioneers in BIM adoption, we're not only shaping structures but reshaping the future of architecture and construction. Through this dynamic methodology, we're forging a path towards more efficient, cost-effective, and sustainable built environments for generations to come.

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