How to Document Existing Conditions of a Building

TL;DR: To document existing conditions of a building you capture a measured, datum-referenced record of what is physically there — structure, services, levels and defects — before you design, renovate or hand over. The reliable way to do it is a terrestrial laser scan (Leica RTC360 or FARO Focus, ±2–5 mm) or a total-station survey (±1–3 mm) tied to GDA2020/MGA2020 horizontal and AHD vertical control, delivered as a registered point cloud plus 2D plans, sections or a Scan-to-BIM model. Get the datum, scope and tolerance right and every downstream decision rests on real numbers, not assumptions.

Key takeaways

• An existing-conditions survey is a measured record, not a sketch — its value is in surveyed coordinates, accurate levels and recorded defects, all referenced to a stated datum (usually GDA2020/MGA2020 horizontal and AHD vertical in Australia).
• Choose the capture method by the tolerance the decision needs: total station for ±1–3 mm steel and machine-base verification, terrestrial laser scanning for ±2–5 mm whole-building geometry, UAV photogrammetry for ±20–50 mm roofs and facades you cannot safely reach.
• Define scope in writing first — level of detail, level of accuracy, which services, and the deliverable format (point cloud, 2D CAD, or a Revit LOD 200/300 model). Vague scope is the single biggest cause of cost blowouts and re-mobilisations.
• Establish and record site control before you measure anything; without a documented datum and control marks, the data cannot be checked, extended, or trusted on the next project.
• Budget realistically: a small commercial fit-out scan might run AUD $2,500–$6,000, while a multi-storey building or industrial plant Scan-to-BIM program runs $15,000–$60,000+. The cost of a clash found on screen is a fraction of one found on site.

What "documenting existing conditions" actually means

Documenting existing conditions means producing a measured, defensible record of a building exactly as it stands — its geometry, levels, structural elements, visible services and any defects — at a known moment in time, referenced to a known coordinate frame. It is the foundation for refurbishment design, heritage recording, dilapidation and dispute evidence, asset and facility management, and brownfield tie-ins where the original drawings are missing, wrong, or decades out of date.

The distinction that matters is between a drawing and a record. Anyone can produce a floor plan that looks plausible. An existing-conditions survey is evidence: every line traces back to a measurement, an instrument, a datum and a date. When a structural engineer designs a new steel frame into an old warehouse, or a contractor prices a fit-out, they are betting money on those numbers. If the survey says a slab falls 35 mm across a bay and it actually falls 70 mm, someone pays for the difference later — usually during construction, at the worst possible margin.

In Australian practice this work spans light commercial fit-outs through to full industrial plants. The principles are identical; only the tolerance, scale and access change.

Step 1: Define the scope, level of detail and level of accuracy

Before anyone mobilises, write down what you are actually capturing. The three questions that govern the whole job are:

• Level of detail (LOD): Do you need walls, floors and primary structure only, or every penetration, conduit, bracket and skirting? More detail means more time on site and more office processing.
• Level of accuracy (LOA): Is this a ±50 mm record for space planning, or a ±3 mm verification of a machine base or steel connection? Specify it; do not assume the surveyor will read your mind.
• Deliverable format: A registered point cloud, 2D CAD plans and sections, or a Scan-to-BIM Revit model at LOD 200/300? Each is a different amount of work downstream of the same site capture.

Confirm which services are in scope — structural, mechanical, electrical, hydraulic, fire — because chasing every cable tray and pipe run doubles the modelling effort over a structure-only record.

Tip: Reference the deliverable to an LOD standard your design team already uses, and put it in the survey brief. "As-built record, structure plus visible services, ±10 mm, delivered as registered E57 point cloud and LOD 200 Revit model" is a scope. "Survey the building" is an invitation to a variation claim.

Step 2: Establish and record site control

Every measurement has to hang off something. Site control is the network of surveyed reference points that gives your data a coordinate frame and lets anyone — now or in five years — check and extend it.

In Australia, current best practice ties horizontal position to GDA2020, projected as MGA2020 in the correct zone (Zone 50 across the Pilbara and Goldfields, Zone 55 across most of the eastern seaboard, Zone 56 for far-east coastal). Levels go on the Australian Height Datum (AHD), given as Reduced Levels in metres. Many sites also run a local building or plant grid offset and rotated from MGA — the survey must publish the transformation between the two.

Set out at least four to six control points, observed with a total station (Leica TS60, Trimble S9) or GNSS RTK (Trimble R12i, Leica GS18) and adjusted as a network. These become the registration targets for the laser scanner and the check points for everything else.

Tip: If the project only needs a stand-alone local grid, that is fine — but still document it with physical marks and recorded coordinates. A survey with no recoverable control is a one-off you cannot build on.

Step 3: Capture the building — choosing the right method

This is where existing-conditions surveys are won or lost. Match the instrument to the tolerance, not to habit.

For most building documentation, terrestrial laser scanning is the workhorse. A Leica RTC360 captures roughly two million points per second and a full dome scan in under two minutes; a typical floor plate might need 15–40 scan setups, each overlapping the last so the cloud registers cleanly. Where you need roofs or high facades, a UAV flown under CASA Part 101 (commercial operations require a Remote Pilot Licence and the operator a ReOC) fills the gaps photogrammetrically. Critical dimensional checks — a lift-shaft plumbness, a crane rail, a sole plate — get picked up with the total station to ±3 mm and used to verify the scan.

Tip: Plan scan positions for line of sight and overlap before you arrive. Occluded areas — behind plant, above ceilings, inside risers — are where "complete" surveys quietly aren't. Flag access for ceiling tiles and riser doors in the scope so they are open on the day.

Step 4: Register, clean and georeference the data

Raw scans are individual clouds in their own local frames. Registration aligns every setup into one coherent point cloud, then ties it to your site control so the whole model sits on MGA2020/AHD (or the local grid). Target-based registration using checkerboard or sphere targets typically achieves cloud-to-cloud agreement of 2–4 mm; cloud-to-cloud registration on geometry-rich interiors can match it.

Cleaning removes the noise that real sites generate — people walking through, forklifts, reflective surfaces, dust, transient objects. The registration report (the residuals between overlapping scans and against control) is part of the deliverable: it is the evidence that the cloud is accurate, and it should be read, not filed.

Tip: Ask for the registration report and a check against independent total-station points. A point cloud with no stated registration accuracy is the laser-scan equivalent of an unsigned drawing.

Step 5: Produce the deliverables — point cloud, 2D, or Scan-to-BIM

The same captured data drives very different outputs, and you only pay to model what you scoped:

• Registered point cloud (E57, RCP/RCS, LAS) — the raw measured truth, viewable in CloudCompare, Recap or Trimble RealWorks. Cheapest deliverable; everything else is derived from it.
• 2D CAD plans, elevations and sections (DWG) — extracted to your line and layer conventions, dimensioned and levelled. Standard for fit-outs and dilapidation records.
• Scan-to-BIM model (Revit, typically LOD 200 for design context or LOD 300 for documentation) — intelligent objects for walls, slabs, columns, structure and modelled services. The most work, and the most useful for a serious refurbishment or digital-twin asset record.

Every deliverable should state its datum, its accuracy, and the survey date in the title block — exactly as a credible as-built drawing does.

Cost considerations

Existing-conditions surveys are priced by area, complexity, access and the deliverable, not by the building's value. The biggest lever on cost is the deliverable: a point cloud is a fraction of a fully modelled LOD 300 BIM of the same building.

As a rough guide: a small commercial fit-out scan with 2D plans runs AUD $2,500–$6,000; a multi-storey building or an industrial plant captured to a Scan-to-BIM deliverable runs $15,000–$60,000+. A single clash caught in the point cloud — a new duct that fouls an existing beam, a mill base that won't sit flat — routinely saves more than the survey cost in avoided rework and lost downtime.

Common mistakes to avoid

Mistake 1: Surveying without defining accuracy

Capturing a building to "as accurate as possible" with no stated tolerance means you can't verify the result and the surveyor can't price it fairly. A ±50 mm space-planning record and a ±3 mm machine-base verification are different jobs with different equipment.

How to avoid: State the level of accuracy in the brief and require an accuracy statement on every deliverable.

Mistake 2: Ignoring the datum

A record with no datum is a floating model. Pull a legacy GDA94 survey into a GDA2020 site model without transforming and everything shifts roughly 1.8 m to the north-east; mix a local building grid with MGA and you get the same problem on a smaller, sneakier scale.

How to avoid: Establish and document control first, and confirm the datum on every drawing and model before you use it.

Mistake 3: Missing the occlusions

Laser scanners only see what is in line of sight. Above ceilings, behind plant, inside risers and under floors are exactly where renovation conflicts hide — and exactly what gets left out of a rushed capture.

How to avoid: Plan setups for coverage, open up ceilings and risers on the day, and supplement with total-station picks or a borescope where the scanner can't reach.

⚠️ Watch out: The most expensive mistake is designing a brownfield modification against an existing-conditions record that is years old. Working buildings change constantly — partitions move, services get added, slabs get re-screeded. If the asset has been touched since the survey date, commission a fresh verification scan before you commit fabrication or construction money.

Frequently asked questions

What is the best way to document existing conditions of a building?

For most buildings, terrestrial laser scanning (Leica RTC360 or FARO Focus, ±2–5 mm) referenced to GDA2020/MGA2020 and AHD control is the most complete and defensible method. It captures the whole geometry once and lets you derive a point cloud, 2D plans, or a Scan-to-BIM model from the same data. Discrete critical dimensions are verified with a total station to ±1–3 mm, and unreachable roofs or facades are filled in with UAV photogrammetry flown under CASA Part 101.

How accurate is an existing-conditions survey?

It depends on method. A total-station dimensional-control survey is typically ±1–3 mm; a registered terrestrial laser scan is ±2–5 mm; GNSS RTK is ±15–30 mm; UAV photogrammetry with ground control is ±20–50 mm. Read and use the record to the tolerance it was captured at — demanding a 2 mm decision from a ±30 mm survey is a misuse of the data.

What deliverables should I ask for?

At minimum, a registered point cloud (E57 or RCP) with a stated datum, accuracy and survey date. Most projects also want 2D CAD plans, elevations and sections. For a serious refurbishment or a digital asset record, ask for a Scan-to-BIM Revit model — LOD 200 for design context or LOD 300 for documentation. Always specify the format up front, because the same site capture supports very different (and differently priced) outputs.

Do I need a registered surveyor?

For statutory, cadastral or boundary-related work, yes — that work must be done or certified by a licensed surveyor. For dimensional-control, as-built and existing-conditions recording of structure and services, the work is done by qualified survey technicians and engineering surveyors, with deliverables checked and signed off. Confirm who is taking responsibility for accuracy on your specific deliverable.

How long does it take?

A single commercial floor plate is often a half to one day of scanning, plus one to two days of office processing for a point cloud and 2D plans. A multi-storey building or industrial plant captured to a full Scan-to-BIM deliverable can run one to two weeks on site and several weeks of modelling, depending on level of detail. Defining scope and access in advance is what keeps both ends predictable.

Get a measured record you can build on

Documenting existing conditions well comes down to three things done in the right order: a written scope with a stated accuracy, a documented datum and control, and a capture method matched to the decision the record has to support. Industrial Spatial Solutions delivers total-station, laser-scan and UAV existing-conditions surveys across commercial, mining, processing and heavy-industrial sites Australia-wide — registered point clouds, dimensioned 2D drawings and Scan-to-BIM models, each with a clear datum and an accuracy you can design against. If you are working off missing or ageing drawings, or you need a verified record before your next fit-out, refurbishment or shutdown, call us on 0407 057 015 for a fixed-price quote scoped to exactly what your engineering decision needs.