Why drains fail in Finchley & Barnet

Finchley & Barnet sits on London Clay with Dollis Hill Gravel on the higher ground, giving way to glacial Boulder Clay north of Barnet. The housing is largely Edwardian and interwar housing through Finchley, Friern Barnet and Southgate, large plots at Totteridge and Hadley Wood, and Victorian stock around Barnet town centre. Those two facts between them explain most of what we dig up here, because the ground decides how a pipe is loaded and the age of the building decides what the pipe is made of.

The Dollis Brook rises near Arkley and runs south through Totteridge and Finchley, and Pymmes Brook drains the eastern side through East Barnet. That matters for drainage because water in the ground and water in the pipe are the same problem seen from two sides: a defect lets one become the other.

In practice, the recurring causes of drainage failure we find across Finchley & Barnet are:

London Clay movement combined with Boulder Clay to the north, both of which shift seasonally and open rigid pipe joints.
Long private drain runs on the larger Totteridge, Hadley Wood and Arkley plots, where a hundred metres of buried clay pipe between house and sewer means many more potential failure points.
Mature tree cover across the whole area, which is high even by outer-London standards.

None of this is unusual or alarming on its own. Buried clay pipework has a service life, and across most of this area that life is either over or close to it. The useful question is not whether a drain will eventually need work, but whether the defect you have now needs a patch, a full lining, or an excavation.

Drain repair in Finchley & Barnet

Drain repair covers structural damage to the pipe: fractures, open joints, displaced sections, deformed pipe, and full or partial collapse. These are the faults that produce blockages which come back within weeks of being cleared, because the clearance removes the debris but leaves the thing that caught it.

We survey the run first with a CCTV camera and code the defects against the standard drain condition classification, so what you are told matches what a surveyor, an insurer or a buyer’s solicitor would independently record. On the ground conditions typical of Finchley & Barnet, the usual outcome is one of three things: a localised patch liner over a single fracture or open joint, a full-length liner where the pipe is defective along its whole run, or an excavation and replacement where the pipe has collapsed and there is no longer a bore to line.

Excavation is the last option rather than the first, and not only on cost. Digging out a drain means taking up whatever is above it, which in a lot of properties here means a driveway, a patio, a rear extension floor or a front garden inside a conservation area. Where the pipe can be repaired from the inside, that is nearly always the better answer.

Drain resealing and relining in Finchley & Barnet

Resealing addresses the joints rather than the pipe body. Older clay drainage was laid in short lengths with mortar or rubber joints, and it is the joints that open first: they take the movement, they let roots in, and they let groundwater and soil out and in. A drain can be structurally sound along every length and still be failing entirely at its joints.

Where the joints have opened but the pipe is otherwise intact, sealing them is a much smaller job than replacing the run. Depending on what the survey shows, that means resin injection into the joint from inside the pipe, a short patch liner bridging the joint, or a cured-in-place liner along the whole length that leaves a continuous jointless pipe inside the old one.

Relining is particularly worth considering in Finchley & Barnet because the ground is wet and mobile. Excavating a trench below the water table here means dewatering and shoring before any pipe is touched, whereas a liner seals the pipe from the inside and stops the groundwater infiltration at the same time.

A cured-in-place liner reduces the internal diameter slightly, so it is not the right answer on a pipe that is already undersized or badly deformed. We say so when that is the case rather than lining something that should be dug up.

Cracked and leaking drain repair in Finchley & Barnet

A leaking drain is often the least visible and most expensive of the three. There may be no blockage at all. What you see instead is damp at the base of a wall, a persistent drain smell in a garden or a downstairs room, ground that stays soft in dry weather, a sinking path or patio, or in the worst cases cracking in the building above where the ground beneath a foundation has been washed out.

On the ground under Finchley & Barnet, that last mechanism is worth taking seriously. River terrace gravel washes into an open joint easily, and with the water table close to the surface there is always water moving to carry it. The result is a void that grows quietly under a path or drive until the surface gives way.

Finding a leak takes more than a camera. Depending on the case we combine CCTV with a dye test to prove which appliance or gully feeds the defect, and a water test to confirm a section is holding before and after the repair. If the drain runs under a building or a boundary, we trace and depth the run from the surface so everyone knows exactly where it goes before anything is opened up.

How a job actually runs

Survey first. A CCTV survey of the affected run, with the defects located by distance from the access point and coded against the standard classification.
A written report and the footage. You keep both. They are yours to take to an insurer, a managing agent, a neighbour or another contractor for a second opinion.
Options, with the trade-offs stated. Patch, full liner or excavation, with what each one does and does not fix, and what it means for the surface above.
The repair. Carried out to the method agreed, not changed on site without telling you why.
A post-repair survey. The same camera down the same run afterwards, so the finished condition is on record and not just described.

If a survey shows the drain is sound and the problem is somewhere else, we tell you that. A blockage that turns out to be a collapsed gully, a disconnected downpipe or a failed rainwater connection is a different job, and pretending otherwise helps nobody.

Whose drain is it?

This question decides who pays, and it catches people out constantly. On 1 October 2011 most private sewers and lateral drains in England and Wales transferred to the local water and sewerage company. In Finchley & Barnet that company is Thames Water.

The short version: the drain inside your property boundary that serves only your property is yours. The lateral drain, meaning the length that continues beyond your boundary to the public sewer, is normally Thames Water’s. A shared drain serving more than one property is usually theirs too, even where it runs under your garden. Where a pipe was laid after the transfer date, or serves only your building, it stays private.

This is worth establishing before any work is agreed, because a defect on a Thames Water asset is generally repaired at their cost, not yours. A CCTV survey that locates the defect relative to your boundary is what settles it. Building control and drainage consents for the area sit with the London Borough of Barnet, and any new connection or build-over of a public sewer needs Thames Water’s agreement in advance.

Areas we cover in Finchley & Barnet

We cover 23 named areas across the EN4, EN5, N2, N3, N10, N11, N12, N14 and N20 postcode districts. If your street is not listed but sits between two that are, we almost certainly cover it, so call and ask.

Arnos Grove N11
Barnet EN5
Bounds Green N11
Cockfosters EN4
East Barnet EN4
East Finchley N2
Finchley N12, N3
Finchley Central N3
Friern Barnet N11
Hadley Wood EN4
Haringey N10
High Barnet EN5
Mill Hill East N3
Monken Hadley EN4
Muswell Hill N10
New Barnet EN4, EN5
New Southgate N11
North Finchley N12
Oakwood N14
Southgate N14
Totteridge N20
West Finchley N3
Whetstone N20

Common questions

How quickly can you get to Finchley & Barnet?

Call 07438 912191 and we will tell you honestly when we can be there, based on where our crews already are that day. We would rather give you a real time than a time that sounds good on the phone.

Do I need a CCTV survey before a repair?

For any structural repair, yes. There is no way to specify a patch, a liner or an excavation without seeing the defect, its position and its extent. Anyone quoting a drain repair without surveying it first is guessing at your expense.

The blockage was cleared and came back. What does that mean?

It almost always means the clearance removed the debris but not the reason it collected there. A displaced joint, a fracture or a section of pipe that has dropped will catch material again within weeks. A survey after clearance is what tells you which of those it is.

Is my drain in Finchley & Barnet my responsibility or Thames Water’s?

It depends where the defect is. Pipework inside your boundary serving only your property is yours. The lateral drain beyond your boundary, and shared drains serving more than one property, generally transferred to Thames Water in October 2011. A survey that locates the defect relative to your boundary is what settles the question, and it is worth settling before you agree to pay for anything.

Nearby areas we also cover

See every area we cover · Drain repair · Drain resealing · Leaking drain repair

Drain Repair in Finchley & Barnet