Drain Relining (CIPP): The Trenchless Repair Method Explained

Drain Relining (CIPP): The Trenchless Repair Method Explained

Drain relining, formally known as cured-in-place pipe or CIPP, has quietly become the default response to most structural drain defects in London. Instead of digging up a garden, pavement or driveway, a resin-saturated liner is installed inside the existing pipe and cured in place. The result is effectively a new pipe within the old one, installed in hours rather than days. This guide explains how CIPP works, when it is suitable, when it is not, and how it compares to traditional excavation on cost, lifespan and disruption.

What CIPP relining actually is

A cured-in-place pipe is a flexible felt or fibreglass sleeve impregnated with a thermosetting resin (epoxy, polyester or vinyl ester), inserted into a damaged host pipe and then cured to form a hard, smooth, structurally independent lining. The liner bonds to the existing pipe walls and bridges cracks, displaced joints, root intrusions and small holes without the need to expose the pipe from the surface.

The method is recognised in BS EN 13566 (plastics piping systems for renovation of underground non-pressure drainage and sewerage networks) and aligns with the wider performance requirements set out in BS EN 752 for drainage systems outside buildings. UK water companies, including Thames Water, use the same techniques on public sewers. The principle is the same whether the pipe is 100 mm clay under a Hackney garden or 600 mm concrete under a high street.

How a CIPP installation actually works

A typical residential lining job in North London follows a clear sequence. The engineer first cleans the host pipe using hydro jetting to remove silt, scale and root mass. A pre-installation CCTV drain survey confirms diameter, defect location and that the line is suitable for lining.

The liner is measured to length and impregnated (wet-out) with the chosen resin under controlled conditions, often in a vacuum table. It is then inserted via an existing inspection chamber using inversion (compressed air pushes the liner inside out into place) or winching followed by inflation. Once positioned, the resin is cured using hot water, steam or ultraviolet light.

UV-cure lining

UV-cure lining uses a glass-fibre composite liner and a train of UV lamps drawn through the pipe at a controlled speed. UV systems cure in minutes, produce minimal waste, and give a thinner, smoother finished pipe wall, but they require the right access. Hot-water or steam cure remains common for 100 mm to 150 mm domestic drains because the equipment footprint is smaller.

After curing, the engineer trims the liner ends at the chambers, reinstates any connections with a robotic cutter if needed, and runs a verification CCTV pass. The whole process for a typical 10 metre run in a residential property normally takes a working day.

When CIPP is suitable

Lining works well for a defined set of defects. Typical candidates include:

• Cracked or fractured clay pipes that are still in line and at gradient.
• Displaced joints with minor offset.
• Root intrusion through hairline cracks once the roots have been removed.
• Internal corrosion or pitting in cast iron stacks.
• Minor holes and longitudinal cracks where the host pipe still provides some structural form.

It is particularly attractive for listed buildings and properties in a conservation area, where excavation under period flagstones, tiled paths or protected landscaping is a significant complication.

When CIPP is not the right choice

Lining cannot rescue every drain. It is generally unsuitable where:

• The pipe has collapsed and lost its bore.
• The line has serious back-fall or deep drain bellies that need re-laying.
• Multiple lateral connections require extensive robotic cutting work that pushes cost beyond an excavation.
• Pipe diameter changes mid-run, which prevents a uniform liner fit.
• The defect is at an inaccessible junction or under a building load that the host pipe can no longer support.

Honesty matters here. Any contractor offering to line everything regardless of condition is selling the technique, not the right answer. A pre-lining survey should determine suitability.

CIPP compared to dig-and-replace

The classic alternative to lining is open-cut excavation: digging down to the failed section, removing it, laying new pipe to BS EN 1401 or BS EN 295 standards, backfilling and reinstating the surface. Excavation is decisive and predictable, but in a London context it is also slow, expensive and disruptive.

Lining usually wins on:

• Time on site. A day rather than several.
• Surface reinstatement. No need to relay block paving, mature lawns or Victorian tiles.
• Neighbour disruption. Minimal noise, no skips, no spoil heaps.
• Access constraints. Works inside terraces, basements and beneath outbuildings where digging is impractical.

Excavation generally wins on:

• Collapsed or severely deformed pipes.
• Realigning incorrect gradients.
• Replacing pipes that have reached the end of useful life across long sections.

Lifespan and warranty expectations

A properly installed CIPP liner is generally specified for a design life of 50 years under typical domestic loading conditions, in line with the durability requirements of BS EN 13566. Reputable contractors offer documented warranties between 10 and 25 years on the lining itself, subject to evidence of correct installation and a verification CCTV survey at handover. Always keep the post-installation video and certificate. It is the document an insurer or future buyer will ask for.

Cost breakdown

Costs depend on access, length, diameter and the cure method. As a rough working guide for a domestic 100 mm to 150 mm drain in London, expect:

• Initial CCTV survey and quotation: lower hundreds.
• Cleaning and root cutting prior to lining: variable.
• Patch repair (short section, 0.5 to 1 metre): mid hundreds.
• Full liner of a single 5 to 10 metre run: low to mid thousands depending on access.
• Post-installation verification CCTV: typically included.

Compared to an equivalent excavation with surface reinstatement, lining is often 30 to 60 percent cheaper once you account for hard landscaping repair, traffic management and skip hire.

Common questions before committing

Two questions come up almost every time a homeowner is offered lining as an option. The first is whether the resin contains anything harmful that could affect the drinking water supply. The drainage pipe carries foul or surface water away from the property, and is separated from the incoming mains supply by an air gap at every fixture. The resins used in CIPP cure into an inert thermoset solid; the system is well established in public sewer renovation and is governed by the same European standards (BS EN 13566) that apply to potable water network rehabilitation in adjacent applications.

The second is whether lining reduces the pipe bore enough to cause future flow problems. Modern thin-wall liners typically add 3 to 6 mm of wall thickness on a 100 mm pipe, a small percentage of the cross-sectional area. Crucially, the new smooth bore has a far lower Manning’s roughness coefficient than the old, scaled clay. Hydraulic capacity often increases after lining, not decreases.

What to expect on the day

A typical residential lining is contained on site. A single van or small truck carries the liner, resin, curing equipment and CCTV gear. Disruption is largely limited to one chamber being open for the working day. Internal water use should be reduced during installation (the engineer will brief the household on timings), but normal use can resume immediately after the final CCTV pass and trimming. Where access is via a front garden or pavement, traffic management is usually limited to a small cone barrier rather than full street licensing.

Working with shared and adopted drains

Many North London terraces share a single foul drain run with one or more neighbouring properties before connecting to the public sewer. Since the 2011 transfer of private sewers, much of this shared drainage is now the responsibility of Thames Water as the sewerage undertaker. Where a lining job is proposed on a section beyond the property boundary, the contractor will normally check the sewer record and, where appropriate, liaise with Thames Water before proceeding. The works themselves may still be appropriate at private cost where they protect a single property, but the planning step matters and reputable contractors do not skip it.

Verification and aftercare

Once installed, a CIPP liner needs essentially no active maintenance for the first decade. The smooth bore resists scale and biofilm formation, and the structurally independent wall blocks root infiltration paths. A pragmatic aftercare plan is a follow-up CCTV drain survey at five years to confirm the liner remains in good condition, plus normal upstream maintenance (gully cleaning, grease control in the kitchen). The certificate and video file from the original installation should be retained with the property documents, since both insurers and future buyers will ask for them.

When to call a professional

If a survey has flagged structural defects, request quotations specifically for lining as well as excavation. For projects in central and inner North London, see drain repairs in NW1 or browse drain repair services. Greater London Drainage offers CIPP lining alongside conventional repair, sized to the defect rather than the technique.

Final thoughts

CIPP drain relining is not a magic fix, but it is a quietly transformative one. Where the underlying pipe still has enough form to host a liner, the technique restores structural integrity, removes infiltration pathways and extends asset life by decades, all without the trauma of excavation. In a city built on Victorian clay and protected hard landscaping, that combination is hard to beat. The right answer for any given drain still depends on a proper survey, but for many London defects, lining is now the first option to consider, not the last.