CAD to Revit: How Irish Practices Prepare Drawings for BIM Modelling

You cannot "just import" a DWG into Revit and call it BIM. This is the most expensive misunderstanding Irish AEC firms have when beginning a CAD-to-BIM transition. The conversion from 2D AutoCAD to a parametric Revit BIM model is not a file format change — it is a fundamental shift in how building information is represented, structured and coordinated. This guide covers the Irish BIM landscape, the pre-conversion preparation that prevents weeks of rework, the modelling workflow by discipline, and the AI-assisted tools now accelerating the process on Irish NDP projects.

The Irish BIM Landscape — Why CAD to Revit Is Accelerating

BIM adoption in Ireland is no longer optional for practices seeking public sector work. The mandate framework is clear:

• OGP (Office of Government Procurement): BIM Level 2 required for public projects above €10m — ISO 19650 information management, IFC coordination output, named CDE
• HSE Capital Estates: BIM required for hospital and healthcare projects above €5m — COBie FM handover data also required
• DoE (Department of Education) school builds: BIM specified in standard brief for projects above the NDFA threshold
• NTA (National Transport Authority): BIM adopted for DART+, BusConnects and major transport infrastructure
• Private sector: Data centre operators (Dublin is Europe's largest data centre hub) increasingly specify Revit BIM from their ELV and M&E design teams — Tier I/II certification requirements drive this

The practical result: any Irish firm working on public sector or enterprise private sector projects above these thresholds that does not have Revit capability — either in-house or outsourced — is effectively excluded from a growing portion of the Irish market.

CAD vs. BIM — What You Are Actually Converting

Understanding this distinction determines how you prepare source CAD files and what the Revit model must achieve:

• AutoCAD DWG: 2D linework, no data, no spatial relationships, no material properties, no parameter inheritance — a digital drawing board, not an information model
• Revit BIM model: parametric objects with data — a wall "knows" it is 200mm thick, composed of a specific masonry type, hosts a door of specified dimensions, sits on a floor level, and feeds a schedule of all similar walls in the building
• What this means for conversion: a line in AutoCAD representing a wall must become a Revit wall family with correct type, material and level assignment — not just a 3D extrusion of the 2D line

LOD Targets for Irish Projects

Preparing Your CAD Files — The Pre-Conversion Checklist

Poor CAD preparation is the single biggest driver of Revit conversion rework. A CAD drawing set where layers are non-standard, geometry is open (unclosed polylines), scale is wrong or xrefs are unbound adds days of cleanup to the Revit workflow. Before handing CAD files to a Revit modeller (in-house or outsourced), run through this checklist:

1. Layer audit: Confirm all layers follow ISO 13567 naming — non-standard layers make it impossible to isolate discipline geometry for Revit import layer mapping
2. Scale verification: Confirm drawing units are millimetres at model space 1:1 — this is the Revit-compatible unit setting. A drawing in metres (common on older Irish civil drawings) must be scaled ×1000 before import
3. Geometry cleanup: Close all open polylines (use OVERKILL command to remove duplicates; PEDIT to close polylines); explode complex blocks that represent walls or elements
4. xRef management: Bind all xrefs (XBIND → BIND option) before export — unbound xrefs do not travel with the DWG to the Revit modeller
5. Coordinate system: Agree on project base point — either set to ITM coordinates, or use a local project origin (0,0) with a noted offset. This is critical for multi-discipline BIM coordination in a federated Navisworks model
6. Purge and audit: Run PURGE ALL and AUDIT to remove unused blocks, linetypes, styles and to fix geometric errors before export
7. Grid lines: Ensure structural grid lines are present and correctly named (A, B, C / 1, 2, 3) — the Revit modeller sets up Revit grids from this CAD reference
8. Levels/datums: Confirm finished floor levels (FFL) are annotated on section drawings — Revit levels are created from this data

Importing CAD Into Revit — Options and Settings

Two primary methods exist in Revit for using CAD as a reference source:

• Link CAD (preferred): The CAD file is linked, not embedded — it remains a live reference that updates if the CAD source is revised. Use this for early-stage modelling where the CAD source is still being updated.
• Import CAD: The CAD geometry is permanently embedded in the Revit file. Use this for final-stage reference where the CAD source is frozen.

Critical import settings:

• Units: AutoCAD mm → Revit mm (confirm this is set correctly — Revit defaults may attempt to import at a different unit)
• Positioning: Use "Shared coordinates" if the CAD file is set to project coordinates; "Centre to centre" for local-grid drawings
• Layer mapping: In Visibility/Graphics (VG), assign CAD layers to appropriate Revit subcategories — this controls visibility and filtering in coordination views

The Modelling Workflow — CAD Underlay to Revit Model

1. Level setup: Create Revit levels from CAD floor plan and section drawings — FFL Ground, FFL 01, FFL 02 etc., matched to Irish Ordnance datum where specified
2. Structural grid: Create Revit grids from CAD grid lines — named to match structural drawings (1, 2, 3... A, B, C...)
3. Architectural: Trace walls over CAD underlay using Revit system families; set correct type (external brick/block cavity, internal plasterboard stud, etc.); assign to levels
4. Structural elements: Model columns, beams, slabs from structural CAD; use Autodesk's structural Revit families or CSC/Tekla Exchange for steel
5. MEP services: Model ductwork, pipework, cable containment from M&E CAD drawings using Revit MEP tools; set systems (supply air, return air, domestic cold water etc.)
6. ELV systems: Model ELV containment, panel locations and device positions from ELV CAD drawings — see our ELV drafting guide for what the source drawings should contain
7. Detach CAD underlay: Once modelling is complete, detach/unload the CAD links — the Revit model is now the source of truth

Scan to BIM — LiDAR Point Cloud to Revit

For refurbishment or extension projects in Ireland where no reliable CAD as-built exists, scan-to-BIM is now the standard approach on projects above €500k. The workflow:

• 3D LiDAR scan registered in Autodesk ReCap Pro → point cloud (RCP/RCS format)
• Point cloud linked into Revit (Insert → Point Cloud)
• Revit modeller traces walls, structural elements, MEP services from the point cloud — achievable at LOD 300 from a good quality scan
• For heritage buildings (Irish Georgian terraces, industrial buildings), scan-to-BIM is the only way to capture complex geometry accurately for planning submissions or Listed Building consent

AI-Assisted CAD to BIM — The 2025 Frontier

AI-powered tools are beginning to automate portions of the CAD-to-Revit workflow that previously required full manual modelling:

• Autodesk AI features in Revit (2025): Automated floor plan interpretation — AI identifies walls, doors and windows from a linked CAD underlay and generates Revit geometry suggestions for human confirmation
• Hypar and Arcol.io: Cloud-based BIM generation from 2D floor plan inputs — effective for repetitive building types (apartment blocks, hotel floors)
• Computer vision pipelines: Image-to-3D model approaches used in research contexts — not yet production-ready for Irish NDP BIM
• Current limitation: MEP routing, structural connections, ELV systems and heritage geometry all still require skilled human modellers; AI accelerates the architectural shell but cannot replace discipline engineering judgement
• ASDV's approach: We use AI-assisted tools where appropriate for standard floor plate repetition, then apply human modelling for MEP/ELV content — delivering LOD 300 models 20–30% faster than fully manual workflows