An as-built survey records what was actually constructed, in position and elevation, and compares it to what the design called for. It is the closing entry in the project's measurement record. Almost every project is built at least slightly differently from the plan, and the as-built is how those differences become part of the permanent documentation instead of being forgotten.
The term is used loosely for a family of related products. A record drawing may be a redlined plan set annotated by the contractor. An as-built survey is a measured survey performed by a surveyor, which is a much stronger document. When someone asks for an as-built, find out which of the two they mean before quoting.
Why the timing dominates everything
The defining constraint of as-built work is that most of what needs recording gets buried. A sewer line is visible for hours; a stormwater chamber for a day; a footing for less than that. Once backfill goes in, the only remaining options are to trust the contractor's notes or to excavate.
So the as-built survey is not one visit at the end of the job. It is a series of visits timed to the construction sequence, and the schedule for those visits has to be negotiated at the start of the project. A surveyor called after the site is paved can produce a competent as-built of the surface and nothing at all of what is under it.
What is typically captured
- Underground utilities before backfill: horizontal position, invert elevations at structures, pipe size and material, and the location of bends, tees and services.
- Structures: rim and invert elevations of manholes, inlets and vaults, and the direction and slope of each pipe entering and leaving.
- Building position: the constructed footprint relative to the property lines and setbacks, and the finished floor elevation.
- Pavement and grading: finished surface elevations sufficient to confirm drainage actually falls the way it was designed to.
- Stormwater management features: basin geometry and outlet structure elevations, from which the as-built storage volume can be computed and compared to the design.
- Site features that affect compliance: parking counts, accessible route slopes, landscape islands, and anything else a permit condition names.
Who requires one, and why
| Requester | What the document is used for |
|---|---|
| Permitting agency | Confirming that the constructed work matches the approved plan before releasing a certificate of occupancy or a performance bond. |
| Utility owner | Adding the new line to the utility's system records so future excavators can be told where it is. |
| Owner and facility manager | Maintaining the asset, planning future work, and avoiding damage during later excavation. |
| Lender or title insurer | Confirming that improvements sit within the boundary and outside easements before final funding. |
| Design engineer | Verifying that the constructed grades and inverts perform as modelled, particularly for drainage. |
| Contractor | Supporting payment applications and defending against later claims about how the work was built. |
Accuracy: it is about consequence, not precision
As-built tolerance should be set by what the number will be used for. A gravity sewer invert is the extreme case: a pipe designed at a shallow slope can fail to drain if the invert is off by a few hundredths of a foot, so those elevations are levelled rather than shot with satellite positioning. By contrast, the horizontal position of a water main to within a few tenths of a foot is entirely adequate, because nothing about its function depends on the exact alignment.
Say what tolerance is required for each class of feature in the scope. A blanket demand for hundredth-of-a-foot accuracy on everything inflates the price and produces numbers whose apparent precision is not real.
Comparing built to design
The comparison is what makes the survey useful, and it should be presented plainly. For each surveyed feature, show the design value, the measured value, and the difference. A table of deviations lets a reviewer scan for the ones that matter rather than reading two drawings side by side.
Where a deviation exceeds tolerance, the survey reports it; deciding whether the work is acceptable is the engineer's call, not the surveyor's. Keep that line clear in the deliverable. A surveyor who writes that a deviation is acceptable has stepped into the designer's role.
pipe slope = (upstream invert − downstream invert) ÷ horizontal distanceRecord surveys and the wider record
Separately from construction as-builts, the term record survey is used for a survey prepared for filing in a public repository, so that the evidence and measurements are preserved for future surveyors. Many jurisdictions require or encourage filing when a surveyor sets monuments or discovers material discrepancies with the record.
The public value of that filing is cumulative. Each filed survey adds recovered monuments, measured geometry and reasoning to a shared body of evidence, so the next surveyor on the block starts from more than a deed. Requirements for what must be filed, and when, vary by jurisdiction, so check the rules of the board or agency where the property lies.
For the same reason, an as-built survey is worth more when it is preserved in a form someone can find in twenty years. A sealed drawing plus a coordinate file with a clearly stated datum is a durable record. A model in a proprietary format with no datum statement is not.