What Causes A Sewer Line Offset?

The most common cause of a sewer line offset is, believe it or not… roots.  The same roots that get inside your sewer line, and cause blockages, also surround the pipe.  Roots will grow where they want to grow, and nothing is going to stop them.  If you have ever seen a 4” thick, concrete sidewalk lifted and broken by roots, that is all the evidence you need.

Clay pipe is the most vulnerable to this, for a couple of reasons, but cast iron is not impervious to it either.  Typically what happens is; the roots find a small hole in the pipe’s hub.  It barely needs to be bigger than microscopic to get in.  Then, as they grow, they surround the hub, and eventually break it.  As the roots surrounding the pipe begin to grow thicker and stronger, they push the pipe out of the way.  This is what causes the offset.

Earth settling or shifting can be another cause for offsets.  This is mostly with clay sewer lines.  With cast iron, it is more common to have the pipes stick together and move as one, creating a “belly” in the line (a loss of grade).  In the category of earth shifting, is the most drastic example of earthquakes.  That said, if an earthquake is strong enough to cause an offset in your sewer main, you likely have more pressing concerns.  Still, when those are sorted out, you may want to look into having a camera inspection done on your sewer, just in case.

What Are the Problems Offsets Cause?

The most obvious problem that offsets cause is that the lack of alignment creates a bottle-neck in the pipe.  Instead of the sewage flowing freely and smoothly, it tends to “hang” on the offset.  This will eventually cause the line to back up.  That “hanging point” can also get a cable machine’s blade stuck, and create problems trying to clear any blockages.

Another problem is that, once the pipe is offset, there is a bigger gap for roots to get in, if there are any in the area (which is likely).  If the roots created the offset, they did so to make more room to get to the sewage (fertilizer). In essence, they have succeeded.  Now, more roots will grow into your line, and get bigger and stronger… sometimes to a point where they can no longer be cut from the line by traditional means.

A third problem is that, having a hole in your pipe, means that sewage is exiting the pipe.  Not only is the untreated sewage seeping into the ground, but water takes dirt with it.  As the water rushes down the pipe, it will take a little of the dirt with it, and wash it down the rest of the line.  That is how sink holes are created.  A sewage sink hole can be a death trap.

How to Repair an Offset Sewer Line

The first step to repairing an offset is to find out if you have one.  It sounds simple, but it is really the key that many people miss.  A savvy plumber can sometimes feel offsets while cabling your line.  It feels different from a normal blockage.  Another sign is the size of the roots that are pulled back, or pulling back a cable with mud on it.

In short, you should never underestimate the value of running a camera down your sewer line.  This is especially true if you have a history of main line backups.  Running a camera is not expensive, and well worth the peace of mind of knowing.  In fact, at Allstar Plumbing, if we run a camera, find a problem, and you have us fix that problem, we won’t even charge you for the camera.  There are other ways to get free camera work as well.  Just give us a call and ask.

Once you have found out for sure that you have an offset, there are basically two ways to fix it.  The most common is to excavate the section of pipe, and replace it.  The excavation needs to uncover enough pipe to be able to get a new piece installed in its place, nice and straight.  The trench may need to be a little longer if the offset caused a loss of grade, as the grade needs to be corrected.

If you find yourself needing a large section replaced, or maybe an entirely new sewer line, you could opt to go trenchless.  Keep in mind though that if you are going with “pipe-bursting”, it may not correct grade problems that sometimes go hand in hand with offsets.

If you need someone to take care of your offset sewer line, or want to know if you might have one, Allstar Plumbing is the right company to call.  Give us a call today!