What Is an As-Built Survey? A Contractor's Field Guide

An as-built survey — sometimes called a record survey or as-constructed drawing — documents what was actually built on a project compared to what the plans called for. It's one of the most frequently required deliverables on civil, utility, and site work projects, and one of the most frequently misunderstood by field crews who have to produce it.

This guide covers what an as-built survey actually is, what data you need to collect, who requires it, and how to produce a professional as-built that gets accepted the first time.

What an As-Built Survey Is (and Isn't)

An as-built survey is field documentation of the final, installed condition of the work. It captures the actual horizontal and vertical positions of constructed features — not the design intent, but the physical reality of what's in the ground or on the site.

It is not the same as:

• The design plans or construction drawings (those show intent)
• A progress survey (that tracks work-in-progress)
• A topographic survey (that captures existing ground conditions before work)

An as-built is specifically a post-construction record: what got built, where it ended up, and at what elevation.

Who Requires As-Builts?

As-built surveys are required by multiple parties on most commercial and public works projects:

Public agencies and municipalities require as-builts before they will accept newly installed infrastructure into their maintenance systems. Storm drain, sewer, water main, and roadway projects all typically require as-built drawings before the agency signs off on the work and releases the bond or retention.

General contractors require as-built records from subcontractors for permit closeout. The GC assembles a complete O&M (operations and maintenance) package that includes as-builts from every trade — structural, MEP, civil, and utilities.

Engineers of record require as-builts to verify the contractor built to plan tolerances and to document any field changes that deviated from the design. Field changes without documentation are a liability problem.

Future owners and operators need as-built information to locate buried utilities, plan future improvements, and maintain infrastructure they can't see.

What Data Does an As-Built Survey Capture?

The specific data collected depends on the scope of work, but the core elements are:

Horizontal Position

• The plan coordinates (northing, easting) or stationing and offset of key features
• For buried utilities: the centerline position of pipes, conduits, and manholes
• For structures: corner coordinates, footprint dimensions, and setback distances

Vertical Elevation

• Invert elevations at every manhole, cleanout, and structure inlet/outlet
• Top-of-pipe elevations at key stations (typically every 25–50 feet on sewer and storm work)
• Final grades at pavement, curb, and drainage structures
• Cover depths over buried utilities

Pipe and Utility Attributes

• Pipe material, diameter, and joint type as installed
• Manhole rim and invert elevations
• Service connection locations and depths
• Valve and fitting locations

Field Changes

• Any deviation from plan alignment or grade
• Substituted materials or pipe sizes
• Added or deleted features approved by the engineer

How to Collect As-Built Data in the Field

As-built data collection works best when it's integrated into the installation workflow, not treated as an afterthought at project end.

The best time to measure is during installation — before backfill covers the pipe. Waiting until after the trench is closed forces you to work from surface features and estimates, which reduces accuracy and can fail inspection.

Standard field methods:

• Total station or GPS rover: Stake coordinates on manholes, cleanouts, and key pipe segments. This gives you horizontal position and elevation in one shot.
• Level and rod: Run a differential level loop to capture invert elevations from a benchmark. Use the Elevation Calculator to verify HI and compute elevations from your rod readings.
• Tape and offset: For simple situations — measure horizontal distance from a known reference (building face, curb, property line) to the feature. Works for service laterals and small features.

Pro tip: Log every shot with a point ID that matches your as-built drawing symbols. Field notes organized by point ID are much faster to draft than notes organized by time or crew member.

What Format Do GCs and Inspectors Want?

Deliverable requirements vary by project, but most as-built packages include:

Plan sheet markups: Red-lined copies of the original construction drawings, with actual-field positions marked in red pen or digitally in red layer. This is the minimum acceptable format for most projects.

Coordinate tables or point lists: A tabular listing of surveyed points with point ID, northing, easting, elevation, and description. Required on most public works projects.

As-built drawings: Drafted CAD drawings (DWG, DXF, or PDF) showing the actual constructed condition. Required for complex utility systems and most DOT projects.

PDF reports: For residential and smaller commercial projects, a formatted PDF showing a plan view, invert elevation table, and grade calculations is often sufficient. Sitemark's as-built generator produces this format directly from field data exports.

Common As-Built Mistakes That Fail Inspection

Missing benchmark reference. All elevation data must be tied to a known benchmark with a recognized datum (NAVD88 or local datum). Relative elevations that aren't tied to a benchmark will fail any public works acceptance review.

Incomplete manhole data. Both the rim elevation and all invert elevations (inlet and outlet) must be recorded at each manhole. Missing one invert is the most common reason an as-built gets rejected.

No documentation of field changes. If the contractor deviated from plan (different alignment, adjusted grade, added a cleanout), the as-built must document it. Undocumented field changes create liability problems that can resurface years later when the utility is excavated for repairs.

Inaccurate grade calculations. Use the Grade Percentage Calculator to verify that your recorded inverts produce the correct pipe grade. Inspectors will check your math.

Wrong coordinate system. If the project is in State Plane or a local grid, make sure your GPS data collection uses the correct coordinate system and datum before you start. Coordinate system errors are nearly impossible to fix after the fact.

How Sitemark Makes As-Builts Faster

Sitemark's as-built generator is built for field crews who need to produce client-ready as-built PDFs without a CAD operator. You enter your job details, upload your data collector export (Topcon MAGNET, Trimble Access, or CSV), and Sitemark formats the invert elevation table, grade calculations, and plan view.

The result is a professional PDF — stamped with your job info, contractor name, and benchmark reference — that passes inspection requirements on residential, commercial, and municipal projects.

The Field Supervisor plan includes the MH-to-MH pipe run tool, which lets you log manhole inverts in sequence and automatically calculate grade for each pipe segment. That output feeds directly into the as-built PDF.

The Bottom Line

An as-built survey is a field documentation deliverable that captures what was actually built. Collect the data during installation, tie everything to a benchmark, document all field changes, and use a consistent format that matches what your GC or agency inspector expects. Producing as-builts with the right data and format the first time is one of the simplest ways to get faster payment and avoid costly re-work requests.