Before lining a sewer with CIPP, verify that the post-lining pipe grade will still meet minimum requirements. This calculator takes your pre-lining survey inverts and liner thickness, and calculates the new invert elevations, post-lining grade, and hydraulic capacity change. Critical for any near-flat sewer run where CIPP is being considered.
CIPP lining raises pipe inverts by the liner wall thickness. For a 12mm liner, that's approximately 0.039 feet per invert. On a 300-foot pipe run at 0.6% grade, that's a drop from 0.6% to roughly 0.57% — still compliant. But on a flatter run at 0.52%, post-lining grade might drop to 0.49%, below the minimum.
A pre-lining grade survey using a pipe laser or level ensures the rehab project won't create a new flow problem. The survey also establishes baseline invert data for the as-built record, required by most sewer authority specifications.
CIPP (Cured-In-Place Pipe) is a trenchless sewer rehabilitation method where a resin-impregnated felt liner is inserted into an existing pipe and cured in place, forming a new structural pipe inside the old one. It restores structural integrity and seals cracks without excavation.
CIPP liner adds wall thickness inside the existing pipe, which slightly raises the pipe invert (flow line). A 12mm liner adds approximately 0.039 ft (12mm ÷ 304.8) to each invert. While small, on very flat pipes near minimum grade, this change can cause post-lining grade to fall below the minimum 0.5%.
The generally accepted minimum post-lining grade for sanitary sewer is 0.5% (6-inch pipe). Some jurisdictions require 0.3% for larger mains. Always verify with the local sewer authority's specifications before proceeding with CIPP on near-flat lines.
Yes, CIPP reduces the pipe inside diameter by 2× the wall thickness, which reduces cross-sectional area and flow capacity. However, CIPP dramatically reduces Manning's roughness coefficient (from 0.013 for old concrete to 0.010 for CIPP), which partially offsets the capacity reduction. For most pipes, net hydraulic capacity is similar or slightly improved.
Liner thickness is designed by a structural engineer based on pipe diameter, depth, soil conditions, live loads, and defect severity. Typical 8-inch sewer liners are 6–12mm. Thicker liners (15–25mm) are used for larger pipes, deep installations, or severely deteriorated hosts.
Calculate post-CIPP-lining pipe inverts, grade percentage, and hydraulic capacity change from pre-lining survey data. Checks minimum 0.5% post-lining grade compliance.
Need a pipe laser for pre-lining grade survey? Spectra DG813 or Topcon TP-L4.
Shop Express Tools →CIPP (Cured-In-Place Pipe) is a trenchless sewer rehabilitation method where a resin-impregnated felt liner is inserted into an existing pipe and cured in place, forming a new structural pipe inside the old one. It restores structural integrity and seals cracks without excavation.
CIPP liner adds wall thickness inside the existing pipe, which slightly raises the pipe invert (flow line). A 12mm liner adds approximately 0.039 ft (12mm ÷ 304.8) to each invert. While small, on very flat pipes near minimum grade, this change can cause post-lining grade to fall below the minimum 0.5%.
The generally accepted minimum post-lining grade for sanitary sewer is 0.5% (6-inch pipe). Some jurisdictions require 0.3% for larger mains. Always verify with the local sewer authority's specifications before proceeding with CIPP on near-flat lines.
Yes, CIPP reduces the pipe inside diameter by 2× the wall thickness, which reduces cross-sectional area and flow capacity. However, CIPP dramatically reduces Manning's roughness coefficient (from 0.013 for old concrete to 0.010 for CIPP), which partially offsets the capacity reduction. For most pipes, net hydraulic capacity is similar or slightly improved.
Liner thickness is designed by a structural engineer based on pipe diameter, depth, soil conditions, live loads, and defect severity. Typical 8-inch sewer liners are 6–12mm. Thicker liners (15–25mm) are used for larger pipes, deep installations, or severely deteriorated hosts.