TryBuildCalc

Drain Pipe Slope Verification Checklist

Essential Checklist+

Complete these critical checks before approving the work or proceeding to the next construction stage.

✓18 Inspection Points
✓6 Verification Categories
✓Slope & Fall Inputs+
  • Correct mode selected — 'Calculate Fall from Slope' when the target slope is already decided, 'Calculate Slope from Available Fall' when the site's available drop is the fixed constraint.
  • Run length used is the actual horizontal developed length of this specific straight run, not the whole drainage system or a straight-line site distance that ignores offsets.
  • Available fall entered (in slope-from-fall mode) is the real, field-measured or drawing-confirmed vertical drop between the two ends of this run, not an assumption.
✓Code Minimum Slope Compliance+
  • Pipe diameter selected matches the actual diameter being installed for this run, not the diameter of an upstream or downstream segment.
  • Code minimum slope check shows a Pass before finalizing the trench grade — a Fail means the slope must be increased, the run shortened, or the invert elevations revised.
  • If the check fails and the available fall genuinely cannot be increased, an Authority Having Jurisdiction (AHJ) variance was pursued and documented rather than installing below the code minimum without approval.
  • For a drain serving a water closet, the 3 inch minimum pipe size was applied regardless of what the DFU capacity table alone would otherwise allow.
✓Line Role, DFU Load & Utilization+
  • Line Role selected (Building Drain/Sewer, Horizontal Fixture Branch, or Stack) matches the actual pipe segment being sized — capacity numbers and the applicable code table differ meaningfully between these.
  • For a Stack, the branch interval count (3 or fewer vs more than 3) matches the actual number of floors/stories the stack serves.
  • Total Drainage Fixture Unit (DFU) load was either built from the actual fixture list serving this segment, or a manually entered total that was independently tallied and double-checked.
  • Utilization percentage was reviewed against Achieved Capacity (not the Hypothetical Capacity figure) before finalizing the design — a mismatch between the two means the pipe as configured doesn't actually deliver the hypothetical number.
  • If the capacity lookup shows 'not permitted' or 'not tabulated,' a different, code-legal slope/diameter/role combination was selected instead of reading a blank result as zero capacity.
  • Confirmed the correct table was used via the Line Role selector — IPC Table 710.1(1) for building drains/sewers, not Table 710.1(2) for horizontal fixture branches/stacks, which is a different (lower) capacity for the same nominal size.
✓Site & Layout Constraints+
  • Trench depth implied by the fall (start invert minus the calculated total drop) stays below the local frost line and above the receiving sewer or septic tank's invert elevation.
  • Venting for this drain segment was sized and placed using the applicable vent-sizing code tables, which are separate from drainage capacity and not covered by this calculator.
✓Installation Verification+
  • Installed pipe slope was field-verified with a level or laser after trenching and bedding, before backfilling — not assumed correct from the design drawing alone.
  • Installed pipe diameter matches the diameter this calculation was run for; a mid-project size substitution needs the slope and capacity check re-run.
✓Final Check+
  • A water test or flow test was performed after installation and before backfill/cover-up, confirming the line drains fully without pooling.
Full QC Checklist+

Verify slope/fall inputs, code minimum compliance, DFU capacity, site constraints, installation, and final checks.

✓35 Inspection Points
✓6 Verification Categories
✓Slope & Fall Inputs+
  • Correct mode selected — 'Calculate Fall from Slope' when the target slope is already decided, 'Calculate Slope from Available Fall' when the site's available drop is the fixed constraint.
  • Run length used is the actual horizontal developed length of this specific straight run, not the whole drainage system or a straight-line site distance that ignores offsets.
  • Available fall entered (in slope-from-fall mode) is the real, field-measured or drawing-confirmed vertical drop between the two ends of this run, not an assumption.
  • Slope entered (in fall-from-slope mode) matches the intended design slope, expressed in inches per foot, not accidentally entered as a percent or a ratio.
  • Resulting slope ratio and percent were cross-checked against the site survey or grading plan where one exists.
  • If metric mode was used, converted imperial figures shown in the results were sanity-checked (e.g. 20.8 mm/m is 1/4 inch per foot) rather than assumed correct.
  • For a Stack line role, this whole section was skipped intentionally — a vertical stack has no slope/fall to check.
✓Code Minimum Slope Compliance+
  • Pipe diameter selected matches the actual diameter being installed for this run, not the diameter of an upstream or downstream segment.
  • Code minimum slope check shows a Pass before finalizing the trench grade — a Fail means the slope must be increased, the run shortened, or the invert elevations revised.
  • If the check fails and the available fall genuinely cannot be increased, an Authority Having Jurisdiction (AHJ) variance was pursued and documented rather than installing below the code minimum without approval.
  • IPC 704.1 / UPC 708.1 (or the equivalent locally adopted code section) was confirmed as the correct minimum-slope reference for the jurisdiction, since local amendments can differ.
  • For a drain serving a water closet, the 3 inch minimum pipe size was applied regardless of what the DFU capacity table alone would otherwise allow.
✓Line Role, DFU Load & Utilization+
  • Line Role selected (Building Drain/Sewer, Horizontal Fixture Branch, or Stack) matches the actual pipe segment being sized — capacity numbers and the applicable code table differ meaningfully between these.
  • For a Stack, the branch interval count (3 or fewer vs more than 3) matches the actual number of floors/stories the stack serves.
  • Total Drainage Fixture Unit (DFU) load was either built from the actual fixture list serving this segment, or a manually entered total that was independently tallied and double-checked.
  • Capacity slope selected in the Building Drain/Sewer capacity lookup matches the same slope actually being installed, not left at a default.
  • Utilization percentage was reviewed against Achieved Capacity (not the Hypothetical Capacity figure) before finalizing the design — a mismatch between the two means the pipe as configured doesn't actually deliver the hypothetical number.
  • If the capacity lookup shows 'not permitted' or 'not tabulated,' a different, code-legal slope/diameter/role combination was selected instead of reading a blank result as zero capacity.
  • Confirmed the correct table was used via the Line Role selector — IPC Table 710.1(1) for building drains/sewers, not Table 710.1(2) for horizontal fixture branches/stacks, which is a different (lower) capacity for the same nominal size.
  • Utilization stays comfortably under 100%, not right at the ceiling, to allow for reasonable future fixture additions on shared building drains.
✓Site & Layout Constraints+
  • Trench depth implied by the fall (start invert minus the calculated total drop) stays below the local frost line and above the receiving sewer or septic tank's invert elevation.
  • Direction changes, offsets, and fittings along the actual run were accounted for separately — this calculator assumes one straight run's geometry, not a multi-segment layout.
  • Cleanouts are placed per code (typically at the building drain's base, at intervals along long runs, and at each change of direction greater than 45 degrees) — outside this calculator's scope but required for a complete design.
  • Venting for this drain segment was sized and placed using the applicable vent-sizing code tables, which are separate from drainage capacity and not covered by this calculator.
  • Where this run connects to a septic system rather than a municipal sewer, the connection was checked against the septic design (see this site's Septic Tank Size calculator) for compatible invert elevations.
  • Trench/stake checkpoints (25/50/75/100% and per-10ft cumulative fall) were used on site to verify grade at intermediate points during digging, not only at the two run endpoints.
✓Installation Verification+
  • Installed pipe slope was field-verified with a level or laser after trenching and bedding, before backfilling — not assumed correct from the design drawing alone.
  • Installed pipe diameter matches the diameter this calculation was run for; a mid-project size substitution needs the slope and capacity check re-run.
  • Pipe bedding and support are continuous and uniform along the run so the pipe can't settle unevenly and create a low spot (a 'belly') that traps water and solids even on an otherwise correctly sloped line.
  • Joints and fittings used are rated for the installed pipe material and match the design (no field substitution of an incompatible fitting type).
  • As-built slope and invert elevations are documented and retained with the project record, especially where an AHJ-approved reduced slope was used.
✓Final Check+
  • A water test or flow test was performed after installation and before backfill/cover-up, confirming the line drains fully without pooling.
  • No visible low spots (bellies) are apparent from a flashlight/camera inspection of the completed run.
  • Final slope, diameter, and DFU capacity figures used are documented for future renovation or troubleshooting reference.
  • Any AHJ-approved deviation from standard code-minimum slope is documented with its approval reference.
Inspection Notes+
Use the latest approved drawings, specifications, and site measurements.
Complete all critical checks before proceeding to the next work stage.
Record deviations and confirm rectification where required.

Related Calculators & Guides

Drain Pipe Slope CalculatorOpen the related calculator and verify the current project inputs.

FAQ

Use it after collecting the project inputs and again before approving or closing the relevant work stage.
No. It supports verification but does not replace approved drawings, specifications, codes, manufacturer requirements, or professional inspection.