TL;DR
An as-built survey is a post-construction survey that documents the actual position, dimensions, and geometry of a completed structure or infrastructure element, comparing it to the approved design to identify and quantify any deviations. It is a standard contractual requirement under Australian construction contracts (AS 4000, AS 2124) and provides the owner with an accurate digital record of their asset at handover. As-built surveys typically use total stations, laser scanners, and GNSS to achieve accuracies of 1 mm to 25 mm depending on the element. The deliverable package includes a deviation report, as-built drawings or 3D model, and a surveyor's certification. In 2025, most major projects in Australia require as-built documentation in both 2D CAD and 3D BIM formats.
Key Takeaways
- An as-built survey documents what was actually built, not what was designed; it identifies deviations between constructed and design positions
- Under AS 4000 and AS 2124, contractors must provide as-built documents before practical completion
- Typical tolerances range from +/- 1 mm for precision equipment to +/- 25 mm for earthworks
- Modern as-built surveys use laser scanning to capture full 3D point clouds, from which deviations are automatically detected by comparing to the design model
- AS 5488 applies when underground services are involved, defining four quality levels (D through A) for subsurface utility information
- The cost of an as-built survey for a medium commercial project ranges from AUD 8,000-15,000; the cost of not doing one includes disputes, rework, and incomplete asset records
Table of Contents
- What is an as-built survey?
- Definition: as-built survey explained
- As-built survey vs design survey: what's the difference?
- When is an as-built survey required?
- The as-built survey process: step by step
- Standards: AS 5488 and other relevant standards
- Equipment and technology used
- Deliverables: what you receive
- Accuracy by element type
- Common challenges and how to avoid them
- Cost of an as-built survey in Australia
- Frequently asked questions
- What to do next
Definition: as-built survey explained
Definition: An as-built survey is a detailed survey conducted after construction or installation is complete to document the actual position, dimensions, levels, and geometry of constructed elements. The survey compares measured as-built conditions against the approved design to identify deviations, quantify them against specified tolerances, and provide a permanent record for asset handover, compliance, and future works.
The as-built survey serves as the bridge between construction and asset management. During design and construction, the project team works with design drawings and models. After handover, the owner and operator need to know what actually exists—because the built reality always differs from the design intent, even when construction is executed well.
Those differences matter for:
- Maintenance access: A pipe routed 200 mm from its design position might block a maintenance corridor
- Future expansion: A column placed 50 mm out of position affects the fit of pre-designed extension steel
- Compliance: Council and regulatory requirements often mandate verification of constructed positions
- Dispute resolution: An independent, measured record prevents arguments about what was built
- Asset management: Accurate spatial data feeds into GIS, CMMS, and digital twin platforms
As-built survey vs design survey: what's the difference?
| Aspect | Design Survey | As-Built Survey |
|---|---|---|
| Timing | Before design begins | After construction is complete |
| Purpose | Provide existing conditions data for designers | Verify and document what was constructed |
| Comparison to design | No—there is no design yet | Yes—measured vs design is the core output |
| Who commissions | Designer or owner | Contractor (usually) or owner |
| Output | Existing conditions model/drawings | Deviation report + as-built records |
| Accuracy | Sufficient for design (typically 10-50 mm) | Matches construction tolerance (1-25 mm) |
When is an as-built survey required?
As-built surveys are required in the following circumstances in Australia:
- Under standard construction contracts: AS 4000 (clause 37) and AS 2124 (clause 35) require the contractor to provide as-built drawings and documentation before practical completion.
- Council development consent conditions: Most local councils in NSW, Queensland, and Western Australia include as-built survey conditions for earthworks, drainage, roads, and building works.
- Infrastructure owner requirements: Water authorities, road agencies, rail operators, and port authorities mandate as-built surveys for any works on their assets.
- Building code compliance: The National Construction Code requires documentation of certain constructed elements for compliance certification.
- Environmental compliance: Mining and development projects often require as-built surveys of rehabilitation, drainage, and erosion control works.
- Quality assurance programs: Large projects include as-built surveys as part of independent verification and validation (IV&V) processes.
- Warranty and defects liability: As-built records establish the baseline condition at practical completion, against which defects liability period claims are assessed.
The as-built survey process: step by step
Step 1: Scope and specification review
The surveyor reviews the construction contract, technical specifications, and design drawings to understand what must be surveyed, what tolerances apply, and what deliverables are required.
Step 2: Control network verification
The surveyor verifies the project control network—ensuring that control points used during construction are still intact and that coordinates have not shifted. New control may need to be established if original marks have been destroyed.
Step 3: Field measurement
The surveyor measures the as-built position of every element specified in the scope. The method depends on the element and accuracy requirement.
| Element | Method | Points Measured |
|---|---|---|
| Building footprint | Total station or laser scanner | Corners, walls, openings |
| Structural steel columns | Total station | Column centres at base and top |
| Concrete walls | Laser scanner or total station | Wall line, openings, penetrations |
| Floor levels | Digital level | Grid of level points |
| Drainage pipes | GPR + excavation or as-laid records | Invert levels, positions, junctions |
| Roads | Total station + laser scanner | Centreline, levels, crossfalls |
| Services (above ground) | Laser scanner or total station | Routes, depths at access points |
| Underground services | GPR, EM, or potholing | Positions, depths (per AS 5488) |
Step 4: Comparison to design
Measured positions are compared to design coordinates. Deviations are calculated in three dimensions:
- Horizontal deviation: Plan distance between measured and design position
- Vertical deviation: Difference in level between measured and design elevation
- 3D deviation: Combined horizontal and vertical deviation (vector magnitude)
Step 5: Tolerance assessment
Each deviation is assessed against the specified tolerance. Common assessment categories:
| Status | Definition | Action Required |
|---|---|---|
| Within tolerance | Deviation <= specified tolerance | None—document and accept |
| Minor deviation | Tolerance < deviation <= 2x tolerance | Engineering review; usually accepted |
| Major deviation | Deviation > 2x tolerance | Rectification or formal acceptance with concession |
Step 6: Reporting and certification
The surveyor prepares the formal as-built survey report, including deviation tables, drawings, and a certification statement. The report is submitted to the contractor and/or owner as part of the handover package.
Standards: AS 5488 and other relevant standards
AS 5488—Classification of Subsurface Utility Information
When an as-built survey includes underground services, AS 5488 defines four quality levels for the information:
| Quality Level | Method | Horizontal Accuracy | Vertical Accuracy |
|---|---|---|---|
| A | Physical exposure (potholing) | +/- 10-50 mm | +/- 10-50 mm |
| B | Geophysical location (GPR, EM) | +/- 100-300 mm | +/- 100-300 mm |
| C | Surface feature survey | +/- 500 mm | N/A |
| D | Desktop records review | Unknown | Unknown |
The construction contract or design brief should specify the required quality level for each service type. Quality Level A is required for clash-critical services where construction will occur nearby. Quality Level B is acceptable for general planning. Quality Levels C and D are not sufficient for construction-phase decision-making.
Other applicable standards
| Standard | Application |
|---|---|
| AS 1100 | Technical drawing standards for as-built documentation |
| AS 4000 / AS 2124 | General conditions of contract requiring as-built documentation |
| Surveying and Spatial Information Act 2002 (NSW) | Legislative requirements for surveys on public land |
| Project-specific specifications | Often define tolerances, formats, and delivery requirements more precisely than standards |
Equipment and technology used
| Technology | Best For | Accuracy | Typical Application |
|---|---|---|---|
| Total station | Discrete point measurement, control | 1-5 mm | Structural elements, bolt positions, levels |
| Terrestrial laser scanner | Full 3D capture, complex geometry | 1-3 mm | Buildings, plant, detailed as-built |
| Drone photogrammetry | Large sites, roof geometry | 2-5 cm | Site topography, progress, large areas |
| Drone LiDAR | Vegetated sites, bare-earth | 2-5 cm | Earthworks, rehabilitation, terrain |
| Digital level | Precise levelling | 0.3-1.0 mm/km | Floor levels, drainage inverts |
| GPR (ground-penetrating radar) | Underground services | +/- 100-300 mm | Service location per AS 5488 |
| EM (electromagnetic) locator | Metallic services | +/- 100-500 mm | Pipe and cable tracing |
Deliverables: what you receive
A complete as-built survey deliverable package typically includes:
1. As-built survey report (PDF)
- Survey methodology and equipment used
- Control network description and accuracy statement
- Design data references (drawing numbers, revisions)
- Tabulated deviation register (measured vs design for every element)
- Tolerance assessment (pass/fail for each element)
- Photographs of critical elements and conditions
- Surveyor's certification statement
2. Deviation register (Excel)
- Item number and description
- Design coordinate (X, Y, Z)
- Measured coordinate (X, Y, Z)
- Horizontal deviation
- Vertical deviation
- 3D deviation
- Specified tolerance
- Status (pass / minor / major)
3. As-built drawings (CAD)
- Drawing files (DWG or DGN) showing as-built positions
- Deviation annotations on each element
- Usually plotted at 1:100 or 1:200 for buildings, 1:500 for site works
4. 3D as-built model (BIM/CAD)
- Point cloud (E57, LAS, or RCP format)
- 3D model in Revit, IFC, or proprietary format
- Colour-coding by deviation magnitude (optional)
5. Utility survey report (if applicable)
- AS 5488 quality level classification for each service
- Location diagrams with quality level annotations
- Caveats and limitations statement
6. Surveyor's certificate
- Formal statement by a registered surveyor certifying that the survey was conducted in accordance with relevant standards
- Instrument calibration details
- Accuracy statement
Accuracy by element type
| Element Type | Typical Survey Accuracy | Typical Tolerance | Common Method |
|---|---|---|---|
| Building footprint | 5-10 mm | +/- 25 mm | Total station or scanner |
| Structural steel columns | 2-5 mm | +/- 10 mm | Total station |
| Concrete walls | 5-10 mm | +/- 15 mm | Scanner or total station |
| Floor levels | 1-3 mm | +/- 10 mm | Digital level |
| Drainage (surface) | 10-20 mm | +/- 25 mm | Total station |
| Drainage (underground) | 100-300 mm | +/- 50-100 mm | GPR or as-laid records |
| Roads (centreline) | 10-20 mm | +/- 25 mm | Total station |
| Roads (levels) | 5-10 mm | +/- 10 mm | Total station or level |
| Services (AG) | 10-20 mm | +/- 50 mm | Scanner or total station |
| Services (UG, QL B) | 100-300 mm | +/- 100 mm | GPR/EM |
| Precision equipment | 1-2 mm | +/- 1-5 mm | Total station |
Common challenges and how to avoid them
| Challenge | Cause | Solution |
|---|---|---|
| Outdated design drawings | Design changes not communicated | Verify drawing revision before starting; hold pre-survey meeting with project team |
| Destroyed control points | Construction activity | Establish redundant control; use wall brackets or deep benchmarks |
| Inaccessible areas | Safety restrictions, operational plant | Coordinate with operations; schedule during shutdowns; use remote methods (scanner, drone) |
| Buried services with no records | Poor as-laid documentation | Use GPR/EM; pothole critical crossings; document limitations clearly |
| Tighter tolerances than practicable | Unrealistic specification | Flag during tender; propose practical alternatives based on industry standards |
| Late engagement | Surveyor brought in after construction complete | Engage surveyor at construction start; schedule as-built survey before demobilisation |
Cost of an as-built survey in Australia
| Project Type | Scope | Cost Range (AUD) |
|---|---|---|
| Small building (residential, small commercial) | Footprint, levels, drainage | AUD 3,000-6,000 |
| Medium building (warehouse, commercial) | Full building, services, site | AUD 8,000-15,000 |
| Large building (multi-storey, complex) | Full building, basement, services | AUD 15,000-30,000 |
| Industrial facility (processing plant section) | Structure, equipment, services | AUD 15,000-40,000 |
| Full processing plant | All structures, equipment, services | AUD 40,000-100,000 |
| Road works (per km) | Alignment, levels, drainage | AUD 8,000-20,000 |
| Underground services only | GPR/EM survey, AS 5488 | AUD 3,000-10,000 |
| Additional BIM modelling | From point cloud or survey | +AUD 5,000-20,000 |
Frequently asked questions
Who is responsible for the as-built survey?
Under AS 4000 and AS 2124, the contractor is responsible for providing as-built drawings and surveys as a condition of practical completion. The contractor typically engages a surveyor and includes the cost in their contract price. For design-and-construct contracts, the design-builder carries this obligation. For owner-managed projects, the owner may commission the as-built survey directly.
How long does an as-built survey take?
A small commercial building takes 1-2 days of field work plus 2-3 days of processing. A medium building takes 2-4 days in the field plus 3-7 days of processing. A full processing plant takes 1-2 weeks in the field plus 2-4 weeks of processing. Underground services surveys add 1-3 days of field work depending on site size and complexity.
What is the difference between an as-built survey and a practical completion inspection?
A practical completion inspection is a visual inspection of the completed works to assess whether they are complete and free of defects. An as-built survey is a measured, geometric verification of positions against design. The as-built survey provides quantitative data; the practical completion inspection is qualitative. Both are typically required at handover.
Can I do an as-built survey with a drone?
Drones are suitable for large-site topography, roof geometry, and visual documentation. They are not suitable for the precise structural measurements that form the core of an as-built survey. A typical as-built survey uses drones for the site-wide context and total stations or laser scanners for the precise building and structure measurements.
What BIM level of detail (LOD) should an as-built model be?
The appropriate LOD depends on the project requirements. For general handover and record-keeping, LOD 200-250 is typical. For facilities management integration, LOD 300-350 may be required. Always specify the target LOD in the construction contract or survey brief. ISS can deliver as-built models at any LOD from 200 to 400.
What happens if deviations exceed tolerance?
The surveyor documents the deviations and reports them to the project engineer. Minor deviations (up to 2x tolerance) are usually accepted with an engineering review. Major deviations (over 2x tolerance) typically require rectification or a formal engineering assessment and concession. The surveyor provides the data; the engineer makes the acceptance decision.
What to do next
An as-built survey is not just a contractual checkbox. It is the permanent record of your asset that will be referenced for decades of operation, maintenance, and future development.
- Check your contract obligations. Review your construction contract for as-built survey requirements before practical completion. Missing this deliverable can delay handover and payment.
- Engage the surveyor early. The best time to plan the as-built survey is at the start of construction. This ensures control networks are preserved, access is coordinated, and nothing is missed.
- Define your deliverables. Specify the format (CAD, BIM, point cloud), the required accuracy, and any specific elements that must be captured. Ambiguity in the brief leads to gaps in the deliverable.
- Budget realistically. As-built surveys typically cost 0.5-2% of construction value. Under-budgeting leads to corner-cutting and incomplete documentation.
Call ISS on 0407 057 015 to discuss your as-built survey requirements. We provide as-built surveying for buildings, processing plants, roads, and infrastructure across Australia, with deliverables in CAD, BIM, and point cloud formats. We will scope the work, confirm the tolerances, and deliver a comprehensive as-built package that satisfies your contract obligations and gives you a permanent, accurate record of your asset.