French Drain Costs UK — What to Charge to Install a French Drain in 2026

What Is a French Drain?

A French drain is a gravel-filled trench containing a perforated or slotted land-drain pipe, wrapped in a geotextile membrane. The membrane and gravel let water in while keeping silt and fine soil out, and the pipe collects that water and carries it away to a soakaway or a legal outfall. It works by giving groundwater and surface water an easier path to travel along than the surrounding ground, intercepting it before it reaches a wall, lawn or patio.

They are typically used where there is damp against walls, a waterlogged or boggy lawn, surface water running downhill toward the house, poor garden drainage on heavy clay, or where water needs intercepting behind a retaining wall. Done properly, a French drain is a low-maintenance, long-lasting fix — which is exactly why customers are willing to pay a fair price for it.

Quick Reference: French Drain Prices UK 2026

What to Charge Per Metre

Most contractors price French drains on a per-linear-metre basis: typically £90–£200 per metre supplied and installed. That spread is wide because the variables are wide — depth, ground conditions and access can double the cost of an otherwise identical run. As a rough guide:

• Small garden run (a few metres, easy ground): £800–£2,000
• Typical domestic French drain (10–25m): £1,500–£4,000
• Larger or landscape-scale scheme: £4,000–£8,000+

Always price off a site visit, not a phone description. The customer who says "just a short drain along the fence" rarely accounts for the clay you'll hit at 400mm, the lack of side access, or the fact that there's nowhere obvious for the water to go. Quote the run, the connection and the spoil disposal as separate lines so the customer can see what they're paying for.

Components and Materials

A properly built French drain is more than a trench full of stone. The core components are:

• Perforated / slotted land-drain pipe: usually 80mm or 100mm flexible perforated land drain, or rigid slotted pipe for longer or steeper runs. The perforations let groundwater enter the pipe along its length.
• Single-size washed gravel or shingle: typically 20mm clean, angular, single-size stone. Single-size is critical — it keeps voids open so water moves freely. Avoid fines or all-in ballast, which clogs.
• Geotextile / permeable membrane: wraps the trench (and often the pipe) to stop silt and fine soil migrating into the gravel and blocking it. This is the single most common thing cheap installers skip — and the reason their drains silt up within a couple of years.
• Inspection chambers and catchpits: let you rod and jet the system, and a catchpit traps silt before it reaches the soakaway or outfall, extending the life of the whole system.

Material cost is a relatively small part of the job — gravel, pipe and membrane for a typical domestic run might be £200–£500. The price is overwhelmingly driven by labour, plant and spoil disposal.

What Drives the Price

Trench Depth and Fall

A French drain must run downhill to an outfall or soakaway — a continuous fall, usually a minimum of around 1 in 80 to 1 in 100. The deeper the trench and the further it has to fall, the more you excavate and the more spoil you generate. A shallow garden interceptor at 300–400mm is a very different job from a 700–900mm drain intercepting water behind a retaining wall.

Ground Type

Ground conditions are the biggest single cost variable. Free-draining sandy or loamy soil digs quickly and cleanly. Heavy clay is slow, sticky, heavy to handle and produces spoil that is awkward and expensive to remove. Hitting rock, old foundations, tree roots or buried services slows everything down. Wet ground may need the trench supported or pumped while you work.

Access for Machinery

A mini-digger transforms the economics of a French drain — it can do in a day what would take a team several days by hand. But it needs access. A 1.5-tonne micro-digger needs around 750mm of clear width; if the only route to the back garden is a 600mm side passage or through the house, you're hand-digging, and your labour cost climbs by £30–£60 per metre. Always check access on the site visit.

Spoil Disposal

Every metre of trench produces spoil, and excavated soil — especially wet clay — is heavy and bulky. You either spread it on site (rarely acceptable to the customer) or remove it. Skip hire and muck-away typically runs £200–£500 per skip, and a decent-sized run can fill two or three. Factor this in explicitly; it's a line item operators routinely underquote.

The Connection Point

Where does the water go? If there's an existing surface-water connection or a ditch you can legally discharge into, the job is simpler. If you need to dig a new soakaway — a crate or rubble-filled pit sized to the catchment — that's a significant extra (£600–£1,800) and its own excavation and spoil. A percolation test should ideally confirm the ground can take the water before you commit to a soakaway.

What's Included in a Typical Quote

A complete French drain quote should set out exactly what the customer is paying for, so there are no arguments at the end. Itemise:

• Setting out the run, levels and fall to the discharge point
• Excavation (by digger or hand) to the agreed depth and width
• Lining the trench with geotextile membrane
• Laying the perforated land-drain pipe to the correct fall on a gravel bed
• Backfilling with single-size washed gravel and wrapping the membrane over
• Topsoil, turf or finish reinstatement over the top (or a stone/grille finish if it's a visible channel)
• Inspection chamber or catchpit where specified
• Connection to the soakaway or outfall
• Spoil removal and site clearance

Worked Example: A Typical Domestic Run

Take a common job: a 15-metre French drain along the rear of a semi-detached house on clay, intercepting surface water running toward the back wall, discharging to a new soakaway. There's side access wide enough for a 1-tonne micro-digger.

• 15m at roughly £140/m supplied and installed: £2,100
• New crate soakaway: £900
• One inspection chamber / catchpit: £250
• Mini-digger hire (2 days) and spoil removal (2 skips): £700

That lands the job around £3,500–£4,000 — sitting squarely in the typical domestic range. Roughly two-thirds of that is labour and plant, which is why getting your access and ground assessment right at the quote stage matters far more than shaving a few pounds off the gravel order. The volume of gravel here is only around 3 m³, a minor cost next to the digging.

Hand-Dig vs Mini-Digger

The decision between hand-digging and bringing in a mini-digger is usually made for you by access. Where a digger fits, use one — it's faster, cheaper per metre and far easier on your team's backs. Budget around £150–£250 a day for a micro-digger plus delivery, and remember it also helps with backfill, spoil handling and soakaway excavation.

Where you genuinely can't get a machine in, price the hand-dig honestly. A 700mm-deep trench in clay by hand is hard, slow work, and trying to compete on price with someone who has digger access will just mean you lose money on the job. Make the access constraint visible in your quote so the customer understands why the price is what it is.

Soakaway vs Outfall

Every French drain needs somewhere for the water to go, and the two main options are a soakaway or an outfall. A soakaway is a pit (crates or clean rubble) that lets collected water disperse slowly into the surrounding ground — it suits sites with reasonably permeable subsoil and where there's no nearby ditch or surface-water drain. An outfall is a discharge into an existing watercourse, ditch or surface-water drain.

Two rules matter commercially and legally. First, never connect land drainage into the foul sewer — water companies prohibit it and it can overload the system. Second, you must be sure the discharge is legal: connecting to a surface-water sewer or discharging to a watercourse can require consent, and on clay sites a soakaway only works if a percolation test shows the ground will actually take the water. Flag these as part of your quote so the responsibility is clear.

Practical Pitfalls

Most French drain failures come down to a handful of avoidable mistakes. Get these right and you'll avoid the callbacks that wipe out your margin:

• No fall: a drain that doesn't run continuously downhill to an outfall or soakaway holds water and does nothing. Check levels along the whole run.
• No membrane: failing to wrap the pipe and gravel in geotextile lets silt migrate in and clog the system within a year or two. The membrane is not optional.
• Wrong gravel: using fines, all-in ballast or pea shingle with too many small particles fills the voids and kills permeability. Use single-size washed stone.
• Foul connection: never connect land drainage into the foul sewer — it's prohibited and can cause backflow and flooding.
• Illegal discharge: always check it discharges legally, with consent where required, and don't pipe water onto a neighbour's land.
• No access for maintenance: without an inspection chamber or catchpit you can't rod or jet the system when it silts. Build in access points.

Quoting Tips — What to Check Before You Price

A French drain quote goes wrong when the contractor prices off the customer's description rather than a proper site survey. Before you commit a price, check:

• Ground type: probe or dig a trial hole. Clay, rock or a high water table change the job completely.
• Levels and fall: confirm there's a viable downhill route to a legal discharge point before you price anything else.
• Access: measure the narrowest pinch point on the route to the work area — it decides digger vs hand-dig.
• Buried services: identify gas, water, electric and existing drainage runs to avoid expensive surprises mid-dig.
• Discharge point: establish whether you're connecting to an existing outfall or building a new soakaway, and whether a percolation test is needed.
• Spoil and reinstatement: agree how much spoil you're removing and what the finished surface (turf, stone, channel) needs to look like.

A short written survey note attached to your quote — ground type, fall, access, discharge plan and spoil — lifts your quote above competitors who just send a number, and protects you if conditions on the day differ from what the customer described.