3D Laser Scanning in Construction: Catching Clashes Before the Steel, Ducts and Joinery Are Made

The ductwork arrives on site, made to the drawings, and it doesn't fit. A beam sits lower than drawn, a sprinkler main runs where the duct should go, or a cable tray nobody recorded fills the gap. Now the duct is remade, the programme slips and someone pays for both.

This brief is for commercial builders, services coordinators and fit-out project managers in Brisbane and SEQ, at design coordination, before anything is ordered for fabrication. It explains how 3D laser scanning in construction catches those clashes in the model instead of on site, how to capture a building that's still occupied, where a point cloud survey stops and a registered survey takes over, and what files you get.

Why fabricated parts don't fit

Most coordination starts from the drawings of what was meant to be built, plus whatever was marked up since. In an existing building, the ceiling space has usually been changed many times: new services threaded through, old ones abandoned in place, beams packed out, trays added. None of it reaches the drawings reliably.

A services model designed to those drawings can be perfect and still collide with reality. Steel, ductwork, pipework and joinery are made to millimetres off site, so the gap between the drawings and the building only shows up when the part is lifted into place.

The workflow: capture, register, overlay

A laser scanner records the existing ceiling space, plant room or riser as millions of measured points. The workflow from there is short:

1. Capture the area from enough scanner positions to see behind beams, ducts and trays.
2. Register the scans into one point cloud in one coordinate system, tied to the project's grid or survey control where it has them.
3. Overlay the point cloud on the services model in Navisworks or Revit, and run the clash check against what's actually there.
4. Resolve each clash with the trade that owns it, then issue drawings for fabrication.

Drag across the section below to see how it works on a typical ceiling space.

Occupied buildings: after-hours and staged capture

Most commercial capture happens in buildings that are still working. Scanning is quiet and battery-powered, so it fits around tenants:

• After hours: capture ceiling spaces, plant rooms and risers outside trading hours, with ceiling tiles lifted and replaced the same night.
• Staged by tenancy: capture one floor or tenancy at a time, registered into the same coordinate system so the stages join up.
• Access planned ahead: keys, inductions, lift access and which tiles can be lifted, agreed with building management before the visit.

Point cloud survey versus a registered survey

A point cloud survey is architectural grade. It's reliable for coordination, clash checking and modelling existing conditions, and it shows things no drawing does. It isn't a registered survey. Set-out, grid lines and anything tied to the legal or engineering datum belong to a registered surveyor.

The rule on site is simple: the surveyor fixes the lines. Where an exact position decides whether a fabricated part fits, such as a steel connection, a penetration or a duct transition, confirm it on site before the part is made.

What you get

A capture for coordination is delivered as files your team already opens: the registered point cloud as .E57, the Autodesk ReCap .RCP and .RCS files for Revit and Navisworks, and, where it's scoped, a Revit model of the existing conditions. The modelling scope is set for each group of building elements, so structure can be modelled in more detail than, say, abandoned cabling. See Scan to BIM Services for the full list of deliverables and levels of detail.

3D laser scanning in construction: FAQs