Level of Development (LOD) in Building Information Modelling

[edit] Introduction

Building Information Modelling relies heavily on clear communication regarding the reliability and specific content of digital models at various stages of a project. The Level of Development framework provides a standardisation system that defines the minimum geometric, spatial, and informational requirements of a model element at different milestones. By establishing a shared language, this framework ensures that architects, engineers, contractors, and facility managers understand exactly how much they can rely on the data presented in the digital workspace. It prevents scope creep and manages client expectations from the initial design phase through to final handover.

[edit] Origins of the Framework

The concept of a standardised scale originated with the American Institute of Architects (AIA) Document E202 in 2008, which introduced the basic numerical scale. Recognising the need for more granular guidance across various trades, the BIMForum subsequently expanded upon this foundation. The BIMForum publishes and regularly updates the Level of Development Specification. This specification offers detailed interpretations and visual examples of how different building systems should appear and function at each level.

Today, this framework is a widely adopted standard in the global construction industry. It plays a critical role in the formulation of a comprehensive BIM execution plan BEP, dictating the exact deliverables required from each discipline at specific project gateways.

[edit] Level of Development vs. Level of Detail vs. Level of Information

A common source of confusion in digital construction is the distinction between Level of Development, Level of Detail, and Level of Information. While practitioners often use these terms interchangeably, they represent fundamentally different concepts.

Level of detail for BIM relates purely to the graphical representation of an element. It describes how closely a digital object resembles the real physical component in appearance.

Level of Information refers to the non-graphical data embedded within the model. This includes manufacturer details, warranty information, performance specifications, and maintenance schedules.

Level of Development encompasses both geometry and data but fundamentally defines the degree of reliability. It dictates how much certainty team members can place in the element's location, shape, and properties. An element might possess a high graphical detail (looking exactly like a specific branded chiller unit) but a low Level of Development if its placement is only approximate for early spatial planning.

It is worth noting that current international standards, such as ISO 19650, have moved towards using the overarching term "Level of Information Need" to encompass these concepts. This modern approach focusses on defining the specific purpose of the information rather than relying strictly on a numerical scale.

[edit] The Six Levels of Development

The standard framework categorises model elements into six distinct levels, ranging from conceptual ideas to verified physical assets.

[edit] LOD 100: Concept Design

At this initial stage, elements are represented as basic conceptual ideas. They might not even possess 3D geometry and could be represented by 2D symbols, generic masses, or preliminary written narratives. The information derived from LOD 100 elements is approximate and primarily used for preliminary spatial planning, early cost estimations, and overall project feasibility studies. For example, a structural column might just be represented by a simple line or a cost per square metre metric.

[edit] LOD 200: Schematic Design

Elements at LOD 200 are modelled as generic systems, objects, or assemblies with approximate quantities, size, shape, location, and orientation. Non-graphic information may also be attached to the model elements. While the model provides a better visual understanding of the building's physical layout, the data remains approximate. Project teams should not use LOD 200 models for precise measurements, definitive cost extraction, or final spatial coordination.

[edit] LOD 300: Detailed Design

This level represents a significant shift towards definitive design. Elements are graphically represented as specific systems, objects, or assemblies with accurate quantity, size, shape, location, and orientation. At LOD 300, the model is reliable enough for generating accurate construction documents and traditional drawings. It allows for preliminary clash detection, although it lacks the granular detail required for installation coordination between different specialist trades.

[edit] LOD 350: Construction Documentation

The BIMForum introduced LOD 350 specifically to bridge the coordination gap between detailed design and fabrication. Elements at this level include the same accurate properties as LOD 300 but add the necessary details for cross-trade coordination and construction layout. This highly critical level includes modelling supports, hangers, base plates, connections, and required operational clearances. LOD 350 models are essential for rigorous clash detection and constructability reviews, ensuring that various building systems interface correctly before any materials reach the construction site.

[edit] LOD 400: Fabrication and Assembly

At LOD 400, model elements feature sufficient detail and accuracy for the fabrication, assembly, and installation of components. This level typically falls under the responsibility of trade contractors and manufacturers. The geometry is exact, and the model includes fabrication tolerances, structural weld details, and complete assembly information. This highly specific data drives automated manufacturing processes and guarantees precise field installation.

[edit] LOD 500: As-Built

The final level represents the project exactly as constructed. Elements are field-verified in terms of size, shape, location, quantity, and orientation. LOD 500 models serve as the foundational database for the Asset information model AIM. They contain all necessary operational data, transferring the digital asset securely to the facility management team for lifecycle operations and maintenance.

[edit] Limitations in Existing Buildings

While the numerical framework excels in new construction workflows, it presents significant limitations when applied to existing buildings and historical structures. The original specification was designed as a forward-looking process, progressing logically from a rough concept to precise fabrication. Applying this forward-looking logic retroactively to an existing asset creates structural and contractual contradictions.

When a surveying team executes a Scan to BIM process to document an existing facility, the resulting point cloud provides highly accurate surface geometry. However, laser scanners cannot penetrate solid walls, concrete slabs, or enclosed ceiling voids. Therefore, a surveyor might accurately model a wall's surface location to a high geometric standard while knowing absolutely nothing about its internal material composition, structural integrity, or the hidden MEP components concealed within it.

Categorising such an element under the standard framework becomes highly problematic. The element possesses high geometric reliability but very low informational certainty. Furthermore, verifying hidden elements in existing buildings often requires destructive testing, which is rarely feasible or cost-effective for the client.

As a result, industry professionals argue that the traditional numerical scale requires careful modification or specific contractual caveats when applied to as-built conditions. Without these caveats, stakeholders might falsely assume a level of internal structural knowledge that simply does not exist in the digital record.

[edit] Related articles on Designing Buildings

• Level of detail for BIM
• BIM execution plan BEP
• ISO 19650
• Asset information model AIM
• Scan to BIM