Side Sewer Defects & Issues

Side sewers are constructed by using several segments of pipes connected by joints. If the joints do not perfectly match up, they are called "offset joints". Offset joints can cause soil and debris can build up in the pipe and eventually lead to sewer backups. Or, if the offset joints are exposed, the soil around the pipe can wash away and leave an empty space. This space can be unstable and eventually lead to sink holes. Here are different examples of offset joints and recommendations for repair.

No repair

Minor offset joint

Buildup of debris is unlikely to cause any negative effects on the sewer system.

Routine inspection

Moderate offset joint

Moderate offset joints cause some debris buildup. Typically would not cause a backup since there is no exposed soil around the joint.

Inspect after a few years. If no change, no repair is necessary.

Repair

Severe offset joint

Surrounding soil may erode into the pipe and lead to voids and cause a backup.

Severe offset joints should be repaired.

Side sewers are constructed at a slight slope of ¼ inch per one foot of pipe. This slope allows wastewater to use gravity to move debris through the pipe. Sags are sections of pipe that don’t have a slope. Sags are typically only a problem if they cause debris to settle and collect in the pipe. Settling debris may eventually result in sewer backups.

No repair

Minor Sag

Minor buildup of debris may occur, but typically not enough to cause negative effects on the sewer. Sags are considered minor if it is less than 25% of the pipe diameter.

Routine inspection

Moderate Sag

A sag 25 to 50% of the pipe diameter would typically cause debris to settle in the pipe which may eventually cause a backup.

Inspect every two to five years.

Repair

Severe Sag

A sag that is 50% or more of the pipe diameter has a higher likelihood for buildup of debris, which may cause a backup over time.

Cracks and fractures are smaller pipe breaks and have various causes. Damage to side sewer pipes can be caused from poor installation, poor soil bedding, root penetration or structural deterioration due to aging pipes.

Routine inspection

Minor Crack/fracture

Typically will have no effect on the working function of the pipe, but may increase in size or severity over time.

Inspect three to five years after original inspection to determine if the severity is increasing.

Routine inspection

Moderate Crack/fracture

May or may not be affecting the working condition of the side sewer; likely will increase in severity over time.

Inspect every one to two years; if the cracks are worsening, begin planning and budgeting for repairs.

Repair

Severe Crack/fracture

Either already has an impact on the working function of the side sewer or is on the verge of collapsing, leading to a full structural failure of the pipe.

Debris (anything besides toilet paper and wastewater) can build up in a side sewer whenever sewer flow is blocked or slowed. Grease can cause a side sewer to drain very slowly or cause a complete blockage of the side sewer. SPU has more guidance on what to flush [Link] and how to dispose of fats, oils and grease [Link].

No repair

Minor Debris/grease

Reduces pipe’s capacity by less than 25%.

Routine cleaning

Moderate Debris/grease

Reduces pipe’s capacity by 25 to 50%.

Routine cleaning; structural repair if a defect is contributing.

Routine cleaning

Severe Debris/grease

Reduces pipe’s capacity to less than 50%.

Routine cleaning; structural repair if a defect is contributing.

Side sewer holes can cause soil and debris to build up in the pipe and may lead to a sewer backup. Or, the hole can cause the soil around the pipe to wash away and leave an empty space. This space can be instable and eventually lead to sink holes. Here are different examples of holes and recommendations for repair.

Repair

Small hole with aggregate showing

Repair

Medium hole with void

Repair

Large hole with void

Roots are a common problem in side sewers. Older concrete and clay pipe side sewers that were not constructed with watertight joints are especially at risk for root damage. Roots are attracted to water and nutrients in the sewer, and can crack pipes and cause sewer backups.

Routine inspection

Minor root intrusion

Typically, minor root intrusions produce no effect on the working function of the pipe.

Inspect three to five years after original inspection.

Routine inspection

Moderate root intrusion

May or may not affect the working function of the pipe. Root intrusions will likely increase in severity over time.

Inspect three to five years after original inspection.

Routine inspection & cleaning

Severe root intrusion

Severe root intrusion, obstructing 50% or more of the pipe can or will affect the working condition of the side sewer.

Inspect every one to two years. Perform routine cleaning.

Many side sewers in Seattle are concrete pipes. Concrete pipes are made of a mixture that includes cement and aggregate (rocks). As the interior cement wall erodes away, the aggregate becomes exposed. This is a common and critical defect in side sewer pipe.

Routine inspection

Minor exposed aggregate

The rocks are just beginning to show through the interior surface of the pipe; will have little to no effect on the function of the pipe.

Inspect three to five years after the original inspection.

Routine inspection

Moderate exposed aggregate

The surface of the interior of the pipe is bumpy from the rocks and porous; will likely not impact the function of the side sewer but the structural stability is decreasing.

Inspect every one to two years and begin planning for repairs.

Replace

Severe exposed aggregate with holes

These pipes are considered to have reached full structural failure even though flows may still be able to travel through or seep out of the pipe.

Replace as soon as discovered.

Property owners are responsible for maintaining and repairing their side sewer. This includes removing roots up to and within the connection to the sewer mainline.

A mass of tree roots coming out of the connection where a side sewer meets the sewer mainline.

Have your side sewer regularly scoped and cleaned, especially in locations with older pipes and dense tree canopy.

Keep your established trees. A tree’s roots will grow up to two times the length of the tree’s height. Therefore, removing trees above or near side sewers will not likely fix a root problem.

If you suspect roots are coming from a tree in the public right-of-way then you can check on whether the City is responsible for that tree by visiting the Seattle Tree Inventory Map site.

We recommend that you file a claim with the City, even if in doubt, and seek reimbursement for your costs in removing the roots from your side sewer. See Filing a Damage Claim for more information.

Damage to the public right-of-way caused by a side sewer or side sewer contractor must be repaired to Seattle Department of Transportation standards. This includes restoring the surface damage to the street.

Winter storms can overload the sewer system when excessive stormwater and groundwater enters sewer pipes through roof gutters, sump pumps, area drains, or cracks and gaps inside sewers.

Any blockages or obstructions in your side sewer will help contribute to sewer backups when your side sewer becomes flooded.

Regular maintenance is required to reduce the risk of sewer backups.

Sharing a side sewer means that the pipe that leaves your property combines with a pipe from a neighboring property (or properties) before it connects to the public sewer mainline.

From the point that your sewer pipe combines with other properties’ pipes, you and your neighbors share maintenance and repair responsibilities.

Two examples of shared side sewers are shown on the map below.

In this example, the owners for properties A and B share responsibility for the side sewer from where their two pipes meet (indicated by the marker) to the connection with the sewer mainline. Likewise, the owners for properties C and D share responsibility from where their two sections of side sewer meet (see marker) out to the connection with the sewer mainline.

Coordinating side sewer repairs with your neighbors

If your shared side sewer needs repair or maintenance, then we would encourage you and your neighbors to come to an agreement on the scope of repairs required and to also agree on which contractor to use to complete the work. We always recommend that property owners get at least three bids from contractors prior to commencing any repair work.

If you have a shared side sewer, there may have been a legal agreement made between the property owners at the time the side sewer was installed that addresses things like property access rights, and responsibility for maintenance and repair of the side sewer. This agreement, known as an easement, is linked to the respective property titles and still applies even if the original property owners have sold the property. 

If an easement exists, then a copy of it will be held by King County. Sometimes the easement recording number can be found on the Side Sewer Card. You can search for your Side Sewer Card at this webpage.

The easement number may be shown on either the front or back of the Side Sewer Card as shown in the examples below.

You can try searching King County records online by visiting their website, however, most of the older records are not available online. You may need to visit their records center in person.