BIM Drafting Services Explained: LOD, BIM Execution Plans and IFC

“BIM drafting” gets used to mean anything from a Revit floor plan to a fully federated, clash-checked model handed over to a facilities team. The difference matters, because it decides what you are paying for, what you receive and whether the model is any use after the drawings are issued. This guide explains what BIM drafting services actually deliver, how level of development is specified, and what to agree before modelling starts.

BIM drafting versus CAD drafting

In CAD drafting the drawing is the product. Plans, sections and elevations are drawn as separate lines, and keeping them consistent is a manual job. In BIM, the model is the product and the drawings are views of it. A wall exists once, with its height, construction and fire rating, and every plan, section and schedule that shows it updates together.

That is why BIM is not simply “drafting in Revit”. A model drawn in Revit with no data behind the elements, or with components modelled as generic shapes, gives you the software cost without the coordination benefit. Revit itself is covered in our guide to Revit drafting services; this article is about the BIM deliverable, whichever authoring tool produces it.

Level of development: how much model you are buying

The single most important line in a BIM scope is the level of development (LOD) required for each element at each stage. LOD describes how far an element’s geometry and information can be relied on. The commonly used scale runs:

• LOD 100 – conceptual. Massing or a symbol showing that something exists, with approximate area or volume.
• LOD 200 – approximate geometry. Generic elements with indicative size, shape and location, suitable for early design coordination.
• LOD 300 – precise geometry. Elements modelled at their designed size, shape, location and orientation, suitable for documentation.
• LOD 350 – interfaces. LOD 300 plus the connections and supports needed to coordinate with other trades.
• LOD 400 – fabrication. Enough detail and accuracy to fabricate and install from the model.
• LOD 500 – as-built. Field-verified elements reflecting what was actually installed.

LOD is set per element type, not for the whole model. A typical design-stage model might hold structure and major services at LOD 350 while furniture stays at LOD 200. Asking for “LOD 400 everything” multiplies modelling time for elements nobody will fabricate from.

The BIM execution plan

On any project with more than one party modelling, the rules are written down in a BIM execution plan (BEP). It is the document that stops a BIM project turning into several incompatible models. A workable BEP covers:

• Roles and responsibilities: who models which disciplines, and who coordinates.
• Model breakdown: how the project is split into files by discipline, building or level.
• Coordinates and units: a shared origin and survey point, so models align when federated.
• LOD requirements by element and stage, as above.
• Naming and classification: file, view and element naming, and the classification system used.
• Exchange formats and frequency: native files, IFC exports, and how often models are shared.
• Clash detection process: tolerances, who runs it, and how clashes are assigned and closed.

The international framework for information management on BIM projects is the ISO 19650 series, and Australian government and tier-1 contractor requirements increasingly follow its terminology; Australian adoptions of international standards are published by Standards Australia, and building requirements by the Australian Building Codes Board. Even on a small job, agreeing coordinates, units and file naming before anyone starts modelling saves days of rework later.

What BIM drafting services deliver

A properly scoped BIM drafting engagement produces more than drawings. Deliverables usually include:

• Discipline models (architectural, structural, mechanical, electrical, hydraulic) at the agreed LOD.
• Drawing sets generated from the model, so plans, sections and schedules agree with each other by construction.
• Schedules and quantities taken directly from model elements: doors, windows, equipment, structural members.
• IFC exports for consultants and contractors using other software.
• Federated coordination models and clash reports where multiple disciplines are involved.
• As-built or handover models carrying the asset information a facilities team needs.

IFC and working across software

Not every consultant on a project uses the same authoring tool. IFC (Industry Foundation Classes) is the open, vendor-neutral format for exchanging BIM data between them. An IFC export is only as useful as its mapping: elements need to export with the right IFC class and with the property sets the receiving party expects, or a structural column arrives as a generic proxy object with no data. Testing an IFC exchange early, with a small sample model, is far cheaper than discovering a mapping problem at the first coordination meeting.

Clash detection and coordination

The coordination value of BIM comes from federating the discipline models and checking them against each other. Hard clashes, such as a duct running through a beam, are the obvious output, but clearance clashes, where there is no room for insulation, access or maintenance, are often the more expensive ones to find on site. Clash detection only works if the models are at a consistent LOD, share coordinates, and are re-run after every significant design change. A clash report that nobody assigns and closes is just a list. Coordination drawings for services are discussed in more detail on our MEP drafting services page.

Questions to settle before a BIM job starts

• Which disciplines are modelled, and by whom?
• What LOD is required for each element type at each stage?
• Is there an existing BEP or client BIM requirements document to follow?
• Which software version and which exchange formats are mandated?
• Who runs clash detection, at what tolerance and how often?
• What is handed over at the end: drawings only, native models, IFC, or a facilities model with asset data?

Clear answers to those six questions are the difference between a BIM model that keeps paying for itself through construction and handover, and an expensive way of producing the same drawings. For architectural documentation built on a BIM workflow, see our architectural drafting services, or contact us to scope a project.