Floor Level Survey

The common alternative is a manometer or water-level floor survey. The physics is sound, but two things usually go wrong with it in practice. The measurements float on an arbitrary reference instead of a benchmark, so a second visit cannot be reliably compared to the first and one building cannot be compared to another. And the survey is very often performed by the company that also sells piers.

We work the other way. A benchmark and control are established first, so every room, unit, and building on the site lands on one datum. Elevations are observed with survey instruments, loops are closed, and independent check points that were not used to establish the surface are observed to prove the work. The closures and residuals go in the report instead of being asserted. A second epoch months or years later returns to the same control, which is what makes movement measurable rather than a matter of opinion.

Grid spacing, the units and vertical datum, and which floors and units are included are set in writing when we scope the job, normally straight from the engineer's requirements. Where a building is badly out of level or heavily obstructed, we add shots at doorways, wall lines, slab joints, and visible cracks so the map shows the breaks and not just a smooth interpolation. For programs that track movement on an interval see deformation monitoring; when the same visit should also capture the building itself see as-built surveys and 3D laser scanning.

Accuracy in this work has three layers and only the third one decides whether the survey is useful. Instrument accuracy is what the equipment achieves on a single observation, and any professional instrument is capable. Registration accuracy is whether the observations agree with each other across the whole floor. Control accuracy is whether they agree with a benchmark, with the building next door, and with the survey somebody runs here next year. We observe with a Trimble S3 total station and, where full-surface geometry is wanted, a Trimble X9 scanner, process in Trimble Business Center, and report elevations relative to project survey control. We hold relative control to better than 0.01 US survey feet on a floor level survey, and on a site where the control is good we are typically inside 0.005 feet. Elevations are reported to the hundredth of a foot. The achieved closures and the check-point residuals go in the report rather than being asserted, because a stated tolerance nobody can verify is worth nothing to a reviewing engineer.

Because we perform no foundation repair and are affiliated with no repair contractor, there is nothing in the result for us either way. That independence is usually the reason an engineer, an HOA board, or an insurer wanted a surveyor in the first place.

Contour takes floor level survey work across Northern California, roughly within three hours of Sacramento. That covers the San Francisco Bay Area, the Peninsula and South Bay, the Sacramento region, the northern Central Valley, and the Sierra foothills. We mobilize for a single unit and for multi-building HOA sites, and we will travel for a portfolio.