When your Central Coast drain has a significant structural problem, you face two fundamental choices: reline it or excavate and replace it. The right answer depends on the specific situation, but for most residential and many commercial scenarios, relining is the clear choice on cost, disruption and outcome. This guide lays out the full comparison so you can make an informed decision.
Quick answer (BLUF)
Drain relining costs 30-60% of excavation and replacement on most residential jobs, takes one to two days vs one to two weeks, causes no garden excavation and requires no council footpath or road permits. Excavation is necessary when the pipe is fully collapsed, needs to change route for a new development, or is located under a slab where access for relining cannot be established. For intact pipes with root, joint or corrosion damage, relining is almost always the better choice.
Side-by-side comparison
| Factor | Drain relining | Excavation + replacement |
|---|---|---|
| Cost (20 m residential sewer) | $5,000, $9,000 | $12,000, $35,000 |
| Time to complete | 1-2 days | 1-2 weeks |
| Garden excavation | None | Full trench along pipe run |
| Concrete/driveway cutting | None | Required if over pipe |
| Tile/floor removal | None | Required if under slab |
| Council permits | Not required | May require road/footpath permit |
| Asbestos handling (AC cement) | Not required | Licensed removalist required |
| Structural outcome | New pipe bore within host pipe | Entirely new pipe |
| Warranty | 50-year product + 10-25 year workmanship | Builder/plumber defects liability only |
| Property disruption | Minimal (water off 2-4 hours) | Significant (trenches, construction zone) |
| Landscaping reinstatement | Not required | Required (lawns, gardens, paths) |
| Tenants can remain | Yes | Often no (or significant disruption) |
| Suitable for fully collapsed pipe | No (without prior point repair) | Yes |
When relining wins clearly
Terracotta pipes with root infiltration and joint damage: The quintessential Central Coast scenario. 1970s Gosford home, terracotta sewer main, recurring blockages from root infiltration. Relining costs $5,000, $7,000 and takes two days. Excavation would require a trench through the established garden, under the path, and potentially under a section of the concrete driveway, $15,000, $25,000 and two weeks of disruption.
AC cement stormwater in a 1970s Wyong estate: Relining encapsulates the degraded AC cement without generating asbestos waste. Excavation requires a licensed asbestos removalist, asbestos waste disposal, dewatering if the water table is high, and reinstatement of the garden. Total cost advantage for relining: very large.
Sewer pipes in established coastal gardens: Properties in Terrigal and Avoca Beach with mature established gardens, the value of those gardens is sometimes tens of thousands of dollars. Excavating through them destroys that value. Relining leaves the garden intact.
Investment and rental properties: Minimal tenant disruption, no extended access requirement, faster return to normal use. A relining job can start and finish during a standard working day.
When excavation is necessary or competitive
Fully collapsed pipe with no bore: If the pipe has collapsed and the bore is completely closed, the liner cannot be inserted. A targeted excavation to remove the collapsed section and install a new coupling section, followed by relining of the remaining pipe, is the hybrid solution. Only the collapsed section requires excavation.
Pipe route change required: If a development or subdivision requires the drain to follow a new route (different alignment, different gradient, new connection points), the existing pipe route is irrelevant, new pipe in a new trench is the only option.
Under concrete slabs with no access: If a pipe runs entirely beneath a concrete floor slab or a thick structural footing, and there is no access point that allows the liner to be introduced, excavation through the slab may be unavoidable. Modern relining equipment can access pipes through quite small entry points, but if there is genuinely no access, excavation is necessary.
Pipe is so severely deteriorated it cannot support a liner: In extreme cases, where the host pipe walls have essentially dissolved or collapsed to the point that even a partially opened bore cannot hold a liner during curing, excavation and replacement is the only option. This is relatively rare in residential scenarios.
When the cost difference is smaller than expected: For very short pipe runs (under 5 m), the minimum job charge for relining may bring the per-metre cost above the excavation alternative. For a 3 m run under a garden bed with easy access, replacement may be comparable in cost.
The hidden costs of excavation
A like-for-like price comparison often understates the true cost of excavation because of costs that do not appear in a basic pipe replacement quote:
Garden reinstatement: Laying turf, replanting garden beds, replacing garden edging and garden lighting, these are real costs that follow any excavation across a garden. Rarely quoted upfront by the plumber.
Hard surface reinstatement: Cutting and reinstating concrete, pavers, tiles or asphalt. The plumber cuts the surface to access the pipe, fills the trench and leaves a concrete patch that does not match the original surface. Full reinstatement of matching concrete or paving is a separate trade, often not included in the base excavation quote.
Asbestos handling: For AC cement pipes, the excavation quote must include a licensed asbestos removalist for pipe removal, double-bagging, transport and disposal at an approved facility. This adds $1,500, $5,000 depending on the volume.
Council permits: Working in a footpath or road reserve requires a council road opening permit and a traffic management plan. Costs vary but $500, $2,000 is typical.
Compaction and settlement: Backfilled trenches settle over time. Cracking of reinstated surfaces over the trench line is common within 12-24 months and may require further reinstatement work.
The hybrid approach: excavate where necessary, reline the rest
For some jobs, the optimal approach combines both methods:
- Excavate a targeted 1-2 m section to deal with a fully collapsed segment or to establish access
- Reline the remaining pipe length from the excavated access point in both directions
This delivers the benefits of relining for the majority of the pipe while addressing the specific section that required physical intervention. It is typically significantly cheaper than full excavation and less disruptive.
FAQs
My plumber says the pipe needs to be replaced, not relined. Should I get a second opinion?
Yes. Some plumbing contractors do not have relining equipment or trained operators. A recommendation to excavate from a contractor who does not reline pipes is not necessarily dishonest, they may genuinely only offer one solution. But it is worthwhile getting a second opinion from a specialist relining contractor who has reviewed the CCTV footage.
Does drain relining last as long as a new pipe?
The product warranty is 50 years for the liner. A new PVC pipe also has an expected service life of 50-100 years. In practice, a correctly installed and warranted liner performs equivalently to a new pipe installation for the same period. The liner does not rust, corrode, or develop the joint vulnerabilities of the original host pipe.
What happens to the old pipe after relining?
It stays in the ground. The old host pipe (terracotta, AC cement or PVC) becomes the permanent outer protection for the new liner. It is not removed. This is why the process works without excavation, the old pipe becomes the formwork.
Can I reline a pipe that has already been partially replaced?
Yes. It is common to have a mixed system where some sections have already been replaced with PVC and older sections remain in terracotta or AC cement. The liner can be installed through the PVC and into the older sections, or the transition junction can be treated as an access point. Discuss the specific configuration with your contractor.