What we talk about when we talk about side sewers.
The diagram at left depicts a typical side sewer where instead of separating household waste water and storm water and routing each to dedicated mains beneath the street, the two are combined and routed to the Sanitary Main only. Rules vary by municipality. Homeowners in King County are responsible for their side sewer (also called lateral) from where it leaves the home up to but not including the tap where it joins the the city main. All Seattle sewer repairs must be permitted and those which enter the public right-of-way (sidewalk, street) must be completed by a Registered Side Sewer Contractor.
COMMON MATERIALS / COMMON ISSUES
Vitrified Clay Pipe
Clay was the dominant sewer material up through 1975. Kiln fired, it has a glass like structure which is all but impermiable to chemicals. Like glass, however, it can break if stressed. In addition, due to the fact that it was sold in short lengths ground movement can cause shifts, or offsets, between joints. While some degree of offset is to be expected, excessive shifts can impede the flow of waste water resulting in blockages. Additionally, offsetting allows sewer water to leach into surrounding soil. Roots divert toward the new source of the water and nutrients, force their way between the joins, and can eventually choke off the sewer. Clay was usually used outside the home beneath landscaping and driveways.
Iron pipe was phased out of residential use in 60s and 70s as less costly PVC stormed the market. Life expectancy varies greatly, with some lines needing replacement thirty years in while others last well past the century mark. Like clay it was assembled in lengths and so can suffer offsets and root intrusion. It can also break. And rust. In fact rust, or scale, can accumulate to such an extent that it will actually stop all flow. Channeling is a related issue. The bottom of the pipe sees constant wetting, and thus, constant rusting. Over time a channel can form. In severe cases this loss of material continues until the entire bottom of the pipe vanishes. Prior to the 70s cast iron was the most common material to be run beneath slabs, therefore open channels - which can allow soil to be washed away - have the potential to destabilize a foundation.
The majority of sewage systems in the U.S are made of concrete. It is inexpensive, widely available, strong, and forgiving. Now used primarily in commercial applications, concrete had its day in the residential sun and is found in homes of all ages. Like clay and iron, concrete lines are assembled from numerous mated short lengths. Offsets can occur, as can breaks and root intrusion. Concrete's chief weakness, however, is that it thins with use. The turbulence of the wastewater itself slowly eats away at the material until eventually fractures and then holes develop. The common lifespan given for concrete is between fifty and one hundred years.
Plastic (ABS, PVC)
The plastics virtually own the current residential sewer market. They are strong, smooth, light, inexpensive, available in long lengths, and simple to assemble. Joints are gasketed or glued, so assuming proper installation (which one can never assume, see image) they suffer neither offsets nor the root intrusions these openings invite. They don't become rough as can happen with rusted cast iron or old concrete - conditions which slow flow and invite bolckages - and due to a degree of flexibility are less likely to break with minor ground movement. Unless a homeowner specifices a different product - and there are valid arguments for the use of any of the aforementioned materials - plastic will likely be used for both repair and new construction.
If your home was built between 1945 and 1972 there is a chance that your sewer system is constructed of Orangeburg pipe. Orangeburg was manufactured as a substitute to cast iron during WW2. Essentially layered compressed tar paper, the pipe has a life expectancy of between thirty and fifty years. Deformation is to be expected, and eventually, total collapse. If your sewer is Orangeburg and is having issues, it will all have to go.
Bellies and FOG
These last two issues can occur with any installation and often are cause for repeat visits from the rooter man. A bellie is a low spot or sag in a length of sewer line, basically an area where the pipe has lost it's 1/4 inch per foot recomended slope. If the sewer is a river, a belly is a lake, and like a lake, the belly is an area of slow moving water where solids tend to fall out of suspension and deposit. Bellies vary in degree, both in depth and length. Minor bellies can have no appreciable effect while a long, completely flooded pipe can cause one backup after another.
Similarly, FOG - deposits of Fat, Oil and Grease - can make a money trap of an otherwise perfect sewer. Cleaning dishes is easiest with hot water, it makes the fats liquid which we imagine helps wash them through the line. The problem is these same fats cool as quickly as they heat and as they travel the cold sewer line they congeal and adhere. Rooting the line only punches a hole in what can be a sewer line packed thick with FOG, a hole which will quickly close again.
...even though we found two breaks, at least we know and can budget. We are getting bids now. So far they are all over the place. Here's to not doing this at Christmas.
Keri B. (Maple Leaf)