Offset Joint in a Sewer Line: How to Read It on Camera
An offset joint is a joint where the two pipe ends no longer line up. One section has shifted up, down or sideways relative to the next, leaving a lip in the flow. On camera you see a step in the pipe wall at the joint, with part of the next pipe’s end face showing.
Offsets are among the most common findings on older clay and concrete laterals. Most are caused by the same thing that causes a belly: the ground moved and the pipe moved with it.
What causes joints to offset
- Settlement. One pipe section settles more than the next.
- Roots. Roots that enter at a joint grow thicker and can push the pipe ends apart. See root intrusion.
- Poor installation. Pipe laid without proper bedding, or joints that were never fully seated.
- Outside loads. Vehicles over shallow pipe, nearby excavation, or soil movement.
- Material. Short sections with many joints (clay tile, older concrete) give more places for this to happen than long runs of glued PVC.
How to read an offset on camera
Look for three things at every joint:
- Is the next pipe opening centered? If the far pipe sits off-center in the frame, the joint is offset. Note the clock position of the exposed lip (for example, “offset, lip at 5 to 7 o’clock”).
- Which way does the step go? If you see the end face of the next pipe (a ledge facing you), the downstream pipe is higher at that point and the lip faces the flow. If the pipe drops away, the downstream side is lower.
- Is there a gap? Dark space or soil between pipe ends means the joint is also separated. Soil or mud on the invert downstream of the joint suggests the gap is letting ground in.
A self-leveling head keeps clock positions true, which makes the report easier to use. See self-leveling vs fixed camera heads.
How PACP codes joint defects
NASSCO’s PACP groups joint defects in the Joint (J) family. The codes below come from the PACP 7 color-coded code chart. Size thresholds (what counts as small, medium or large) are defined in the PACP manual for the version you code to; check the current manual rather than guessing.
| PACP code | Meaning | What it describes |
|---|---|---|
| JOS / JOM / JOL | Joint offset small / medium / large | Pipe ends displaced, not lined up |
| JOSD / JOMD / JOLD | Joint offset small / medium / large defect | Separate “defect” variants listed in the chart; see the manual for when they apply |
| JSS / JSM / JSL | Joint separated small / medium / large | Pipe ends pulled apart along the axis |
| JAS / JAM / JAL | Joint angular small / medium / large | Pipe ends at an angle to each other |
Even if you don’t code to PACP, using the same vocabulary helps. “Offset” and “separated” mean different things to a lining contractor or a municipal reviewer, and mixing them up in a report causes confusion.
NASSCO has also published guidance noting that not every joint that looks separated is coded as separated, which is a good reminder to watch the joint as the head moves through it rather than judging from a single frame.
Severity: what matters to the customer
| Condition | Likely impact | Typical recommendation |
|---|---|---|
| Small offset, no gap, no debris | Often none | Note it, re-scope later |
| Offset with lip catching paper or grease | Recurring slow drains or stoppages | Clean, then repair the joint |
| Offset with roots | Roots return after cutting | Cut, then line or spot repair |
| Offset with gap and soil visible | Ground washing in, risk of voids | Repair soon |
| Large offset the camera cannot pass | Flow restriction, possible break | Excavate |
Repair options
Spot repair (dig). Excavate at the joint and replace the section, or reconnect with a shielded coupling. Your footage and a sonde locate put the dig in the right place. See sewer cameras with a locator.
Sectional (point) liner. A short cured-in-place liner over the joint seals the gap and smooths the transition, if the offset is small enough for the liner to pass and seat properly.
Full-length lining. When there are offsets at many joints, lining the whole run can make more sense than several spot repairs, again depending on how large the offsets are.
Replacement. Pipe bursting or open-cut replacement when offsets are large, numerous, or combined with breaks and bellies.
What to put in the report
For each offset joint, give the footage, the clock position of the lip, whether the downstream pipe is higher or lower, and whether there is a gap, roots or soil at the joint. If the camera could not pass, say so and give the footage where it stopped. A still image of each significant joint, with the counter visible, makes the written report easy to check against the video later.
Record the lip and gap at each offset with the head stopped, lit well, and footage visible on screen. A lining contractor quoting from your video needs to see the size of the step, not just that a joint exists.
FAQ
Is an offset joint the same as a separated joint?
No. An offset joint is displaced sideways or vertically, so the two pipe ends no longer line up. A separated joint has pulled apart along the axis, leaving a gap. PACP codes them separately (JO for offset, JS for separated), and one joint can show both.
Can a sectional liner fix an offset joint?
Often, if the offset is small enough for the liner and its packer to pass and seat. A large offset may block the liner or leave a lip under it. The lining contractor makes that call from your video, so record the offset clearly at the joint.
Why does my camera snag at some joints and not others?
The head hangs up when the downstream pipe sits higher than the one you are in, because it hits the face of the next pipe. Pushing through a joint where the downstream pipe dropped, the head falls off the step instead, but it can catch on the way back.
Do offset joints cause backups by themselves?
A small offset may never cause a problem. A lip that faces the flow catches paper and grease, and a gap at the joint lets roots and soil in. Backups usually come from what the offset collects, not the offset alone.