---
title: "What is BIM? Building Information Modelling"
description: "PAS 1192-2 describes Building Information Modelling (BIM) as the process of designing, constructing or operating a building or infrastructure asset using electronic object-oriented information, forming a reliable basis for decisions throughout the project life cycle."
published: "2025-03-19"
author: "PETRUF Consulting Engineers"
url: "https://www.petruf.ie/blog/what-is-bim"
---

# What is BIM? Building Information Modelling

> PAS 1192-2 describes Building Information Modelling (BIM) as the process of designing, constructing or operating a building or infrastructure asset using electronic object-oriented information, forming a reliable basis for decisions throughout the project life cycle.

Three definitions, all saying the same thing in different words, are the quickest way into what [BIM](https://www.petruf.ie/services/building-information-modelling) actually is.

- PAS 1192-2 describes it as the process of designing, constructing or operating a building or infrastructure asset using electronic object-oriented information.
- ISO 19650-1 describes it as the use of a shared digital representation of a built asset to facilitate design, construction and operation processes, forming a reliable basis for decisions.
- BRE puts it plainly: getting the right information to the right people in the right format at the right time.

So BIM is the correct management of project information and process across the whole life cycle of a project.

## BIM maturity

Maturity runs from Stage 1 to Stage 3 in the ISO series, which the older PAS documents numbered Level 0 to Level 3.

- Stage 1 is the use of BIM enabled software in a way that is not structured to the ISO, which is sometimes called lonely BIM.
- Stage 2 is the use of BIM enabled software with the correct structured processes, common data environments, federated models and the supporting documentation.
- Stage 3 is not yet reachable in practice, and is likely to remain an aspiration for some time.

## Who does what on a project

- Client, or lead appointing party.
- Employer, which can be anyone employed by the client.
- Lead supplier, or lead appointed party: the project lead, usually the architect.
- Appointed party, or task teams: the rest of the design team.

## The dimensions

- 2D: line work, which is CAD and drawings.
- 3D: object modelling.
- 4D: time, which is the 3D model with the programme attached.
- 5D: cost, which is the 3D model with estimating attached.

## The standards

The ISO 19650 series is the reference, and the documents below are what it asks a project to produce.

- OIR, organisational information requirements: what the client needs at organisational level.
- AIR, asset information requirements: the OIR read by the client's own professionals to work out what information the asset needs, and therefore whether an architect or engineers are required.
- EIR, exchange information requirements: the client's brief.
- BEP, BIM execution plan, pre and post appointment: how the project will actually be executed.
- AIM, from the AIR, the asset information model: the information needed to operate the asset across its life, such as data sheets and instruction manuals.
- PIM, from the EIR, the project information model: the information developed about the asset during design and construction, which is the models themselves.

Get those right and BIM stops being software and starts being the thing it is defined as: the right information, to the right people, at the right time. What that looks like on a real job is set out in [BIM implementation in precast concrete](https://www.petruf.ie/blog/bim-implementation-in-precast-concrete).

## What people ask after reading this

### What is BIM, in one sentence?

The correct management of project information and process across the whole life cycle of a project. PAS 1192-2 puts it as designing, constructing or operating a building using electronic object oriented information.

### What are the BIM stages?

Stage 1 to Stage 3 in the ISO series, which the older PAS documents numbered Level 0 to Level 3. Stage 1 is BIM enabled software used in a way that is not structured to the ISO, which is sometimes called lonely BIM.

### What do the dimensions mean?

2D is line work, which is CAD and drawings. 3D is object modelling. 4D is the 3D model with the programme attached. 5D is the 3D model with estimating attached.

### Which standard governs it?

The ISO 19650 series, which sets out the information requirements a project has to produce, from the client's organisational requirements down to the exchange information requirements on a single appointment.

## Sources

- [BIM certification, National Standards Authority of Ireland](https://www.nsai.ie/certification/bim-certification/)
- [Public sector BIM adoption timeline, Capital Works Management Framework](https://cwmf.gov.ie/en/resources/bim/public-sector-bim-adoption-timeline/)