Short definition
Slip lining is a trenchless rehabilitation method that inserts a smaller-diameter new pipe — typically continuous HDPE — inside an existing host pipe. The annular space between the new pipe and the old is grouted to lock the liner in place and stop groundwater infiltration. Result: a new pipe inside the old one, with a slightly smaller bore.
What it is
A crew opens an entry pit and a receiving pit at the two ends of the segment being lined. A pre-formed length of HDPE — fused on-site or pre-fabricated — is then pushed or pulled through the host pipe. Once seated, the gap between the new pipe’s outside and the old pipe’s inside is filled with cementitious grout. The grout prevents the liner from collapsing under load and stops groundwater from migrating along the annulus.
For residential side sewers, slip lining is less common than CIPP or pipe bursting because the bore reduction is meaningful at small diameters — going from a 4-inch clay tile to a 3-inch HDPE liner cuts hydraulic capacity noticeably. Slip lining sees more use at larger diameters: municipal storm sewers, large-diameter sanitary mains, and commercial-scale rehabilitation.
Why it matters to a homeowner
Most homeowners shopping trenchless options will hear CIPP and pipe bursting quoted; slip lining shows up rarely, and when it does it’s usually because of an unusual constraint — a short straight run, an oversized host pipe, or a structure where bore reduction is acceptable. If a contractor proposes slip lining for a residential side sewer, ask why CIPP or bursting wasn’t preferred.
The trade-off to understand: slip lining is sometimes slightly cheaper than CIPP and somewhat less invasive than open-trench, but the smaller bore can become a flow problem if the household has high simultaneous demand or any history of solids carry. CIPP keeps the original bore; pipe bursting gives the same or larger bore.
Common variants and not the same as
- Slip lining vs. CIPP. CIPP forms a new pipe in place from a resin-impregnated felt or fiberglass tube; the cured pipe matches the host bore closely. Slip lining inserts a pre-formed pipe of smaller diameter.
- Slip lining vs. pipe bursting. Bursting fragments the old pipe and pulls a new one of equal or larger bore through the resulting cavity. Slip lining inserts a smaller pipe inside without disturbing the old.
- Continuous HDPE slip lining vs. spiral-wound. Continuous HDPE is the standard residential-relevant form. Spiral-wound (a strip wound into a tube on-site) is an alternative for situations where continuous insertion is impractical.
Common limitations
- Bore reduction — flow capacity drops, sometimes significantly. Often acceptable on oversized storm sewers; rarely ideal on a 4-inch residential lateral.
- Cannot follow severe joint offsets — the host pipe must still hold a continuous channel large enough for the liner.
- Requires entry and receiving pits at both ends of the segment.
- Annular grout failure — if the grout doesn’t fill cleanly, groundwater migrates through the void and undermines the host.
Washington note
Slip lining is most commonly seen in WA on municipal storm-drain rehabilitation — King County, SPU, and Tacoma have all used it on larger-diameter pipe upgrades. On residential side sewers, it shows up rarely, and Seattle and Tacoma side-sewer permits more often reference CIPP or pipe bursting as the trenchless options. If you receive a slip-lining quote for a residential side sewer, get a comparison quote for CIPP or bursting before committing.