How accurate must CIPP invert measurements be?

CIPP invert measurements must be within ±0.02 ft (approximately ±0.25 inch), which is significantly tighter than new sewer installation as-built requirements (typically ±0.10 ft). This tighter requirement exists because CIPP follows the existing pipe -- the liner must match existing slope, and without accurate pre-lining inverts, there is no baseline to verify the liner was installed correctly. Many cities reject CIPP as-builts that use tape measure inverts rather than level survey inverts for this reason.

What happens without a pre-lining survey record?

Without a documented pre-lining survey, the city or utility owner has no baseline to verify whether the CIPP liner was installed to the correct slope. If the liner sags or experiences flow problems after installation, there is no way to determine whether the problem existed before rehabilitation or was caused by the rehabilitation process. Most city specifications now require the pre-lining survey as a contract deliverable, and projects without it may not receive final acceptance.

CIPP Pre-Lining Survey Documentation Requirements

Updated May 2026 · 6 min read

Quick Answer

What data is required for a CIPP pre-lining survey?

A CIPP pre-lining survey must document manhole rim and invert elevations at every MH (±0.02 ft accuracy), pipe slope between manholes, pipe diameter and material, condition notes from CCTV inspection, and GPS coordinates. Accuracy requirement is ±0.02 ft — much tighter than new install as-builts — because the CIPP liner must follow existing slope exactly.

±0.02 ft

Required accuracy

±0.10 ft (looser)

vs new install

Yes — condition baseline

CCTV required

What Is a CIPP Pre-Lining Survey?

Before cured-in-place pipe (CIPP) rehabilitation can begin, the existing pipe conditions must be documented in a pre-lining survey. This baseline record establishes the existing invert elevations, pipe slopes, pipe condition, and manhole schedule before any rehabilitation work occurs.

The pre-lining survey serves two purposes: (1) it documents the existing condition so that the rehabilitation can be designed to the correct slope, and (2) it creates a baseline for post-lining verification -- you cannot verify the liner was installed correctly without knowing what the pipe was before rehabilitation.

Required Data

A complete pre-lining survey must include:

Manhole rim elevations -- surveyed with a level or total station, ±0.02 ft accuracy
Invert elevations -- all inverts in and out at each manhole, ±0.02 ft accuracy
Pipe slope -- calculated from invert elevations, compared to design slope
Pipe diameter and material -- VCP, RCP, concrete, DIP, HDPE
Pipe condition notes -- from CCTV inspection: offset joints, roots, cracks, sags, infiltration
GPS coordinates -- of each manhole, northing/easting to 0.1-foot accuracy
CCTV video archive -- referenced by date and inspection ID

Accuracy Requirements

Pre-lining invert elevations must be surveyed within ±0.02 ft -- the same accuracy standard as the post-lining verification. This is much tighter than a new sewer as-built (typically ±0.10 ft) because CIPP must follow the existing pipe slope. A pre-lining survey done with a tape measure to the nearest 0.1 ft is not adequate for CIPP work.

The ±0.02 ft requirement means you need a properly set up level or total station, not a tape measure from the rim to the invert. Cities with experience in CIPP have learned this the hard way -- they now specify ±0.02 ft in their specifications explicitly because of problems with tape measure surveys in older contracts.

Post-Lining Verification

After CIPP installation, re-survey the same manhole inverts to verify the liner was installed to the correct slope. Compare to the pre-lining baseline. Any deviation greater than ±0.02 ft should be investigated -- liner sags create sediment accumulation points that cause long-term flow problems.

The post-lining survey, with comparison to the pre-lining baseline, is the primary as-built deliverable for CIPP rehabilitation projects. Cities that have been through failed CIPP installations require both surveys in the as-built package.

Equipment

Pipe lasers and level equipment for accurate CIPP pre-lining invert surveys.

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Document CIPP Pre-Lining Surveys Digitally

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