Architectural BIM

[edit] Introduction

Architectural Building Information Modelling (BIM) is the use of BIM processes to create, manage and exchange digital information relating to the architectural aspects of a built asset. An architectural information model can contain three-dimensional representations of building elements together with associated graphical and non-graphical information. It can support the development and communication of design intent, design coordination, construction planning, quantity information and the operation and management of the completed asset.

An architectural model forms part of the wider information-management process rather than being a standalone three-dimensional representation. Its content, level of detail and level of information should be determined by the information requirements of the project and the decisions that the information is intended to support.

[edit] Architectural model elements

An architectural model can represent the principal elements of a building, including walls, partitions, floors, roofs, ceilings, doors, windows, stairs, ramps, spaces and architectural finishes. Depending on the purpose of the model, elements may contain information about materials, dimensions, performance characteristics, classification, specification, location and other properties.

Walls and partitions can be modelled as individual elements or as assemblies incorporating layers such as structural components, insulation, cavities and finishes. Floors, roofs and ceilings can similarly contain information about their constituent layers and finishes. Doors and windows can be represented as reusable parametric objects, allowing their dimensions and associated information to be changed consistently where appropriate.

Stairs, ramps, balustrades and other circulation elements can be modelled according to the requirements of the project. Architectural details such as mouldings, cornices, façades and other features may also be incorporated where they are relevant to the required information. The amount of geometric detail should be proportionate to the purpose of the model, as unnecessarily detailed modelling can increase file size and processing requirements without providing additional useful information.

[edit] Application to new and existing buildings

For new buildings, architectural BIM can be used from the early stages of design through to construction and handover. The model can represent spatial arrangements and design intent, support the production of drawings and schedules, provide information for design coordination, and contribute to analysis and assessment. As the project develops, the information in the model can be progressively refined in accordance with the project's information requirements.

BIM can also be used for existing buildings, including refurbishment, alteration and conservation projects. One approach is scan-to-BIM, in which survey information such as point clouds generated by laser scanning is used as a basis for creating an information model. Point cloud data normally requires processing, registration and alignment before it can be used for modelling. Elements are then modelled to an agreed level of accuracy and information, based on the intended uses of the model.

The accuracy of an existing-building model depends on the quality of the survey information and the modelling methodology. Areas that are inaccessible or obscured during surveying may contain incomplete or uncertain information. Such limitations should be identified and communicated rather than implying a level of accuracy that the source information cannot support.

[edit] Standards, information requirements and coordination

Architectural BIM should be developed in accordance with the information requirements and information-management arrangements established for the project. In the UK, the ISO 19650 series provides the principal framework for managing information using BIM. PAS 1192-2:2013 was an earlier UK specification for information management during the capital/delivery phase and was subsequently replaced by the ISO 19650 approach.

The required content of an architectural model should be established through the project's information requirements and information delivery processes. This may include requirements for geometry, classification, specifications, performance data, asset information and other non-graphical information. Information should be provided at the point at which it is required rather than automatically modelling every element to the highest possible level of detail.

The terms Level of Detail (LOD) and Level of Development are used in some BIM frameworks, particularly in relation to the description of model content and graphical development. They should not be treated as universally interchangeable terms. Different standards and organisations use different definitions and numbering systems, so the applicable definition should be established for each project. In the ISO 19650 approach, information requirements and the required level of information need provide the basis for determining what information should be delivered.

Architectural information models are normally coordinated with other discipline models. A federated model can bring together separate architectural, structural and building services models without merging them into a single model. This allows the project team to review the combined information and identify potential spatial conflicts, coordination issues and other problems.

The architectural model commonly establishes building geometry, spaces, floor levels, partitions and other spatial constraints that need to be coordinated with structural elements and building services. Coordination can include checking the positions of structural members, ducts, pipes, cable containment, equipment, access zones and maintenance spaces. The architectural model may also be used to support the coordination of drawings, schedules and other project information.

A common data environment (CDE) provides an agreed process and location for collecting, managing and disseminating project information. It can contain graphical models, documents and structured non-graphical information and supports the controlled sharing of information between project participants.

[edit] Quality assurance and limitations

Architectural information models should be subject to quality assurance throughout their development. Checks may include the accuracy and completeness of geometry, consistency of naming and classification, compliance with information requirements, correct positioning of elements, appropriate levels of information and coordination with other discipline models.

The reliability of an architectural BIM model is dependent on the quality of the information from which it is created and the processes used to develop and check it. For existing buildings, survey accuracy and access limitations can affect the reliability of the model. For new buildings, design changes and incomplete information can result in discrepancies if the model is not appropriately maintained.

Highly detailed models can require substantial processing capacity and additional modelling time. Interoperability can also present challenges where information is exchanged between different software applications or file formats. Open and standardised information formats, including Industry Foundation Classes (IFC), can support information exchange, although conversion between systems may still result in differences in geometry, properties or other information.

Architectural BIM is therefore most effective when the model's purpose, information requirements, responsibilities, exchange processes and quality standards are established at the outset and maintained throughout the relevant stages of the asset lifecycle.

[edit] Related articles on Designing Buildings

• Building Information Modelling BIM
• Common data environment CDE
• Federated building information model
• Project information model PIM
• BIM execution plan
• Asset information model AIM
• Industry Foundation Classes
• Interoperability
• BIM dimensions, maturity and levels of development
• Step-by-step guide to using BIM on projects