Drainage contractor UK: when a garden drain stops being DIY

The lawn is still soft two days after rain, and the low corner by the extension is the worst of it. You have paced out a trench, looked at white fleece and a perforated pipe, and then realised the water on the paving is coming off the roof, or that the only pit you can dig sits against the wall. A drainage contractor in the UK is the right next call for that job. A folded cut of geotextile is a liner. It is not a soakaway design, a building-control submission, or a check for the cable under the grass.

In short

You can still line a short, shallow lawn trench yourself, and you can still buy the non-woven fleece for it. Hire someone when the soakaway takes water from a building, you cannot keep the clearance the English notes describe, the ground needs a digger, buried services are unclear, or the job needs a datasheet the shop title does not print.

Jobs that stay in the garden

A short French drain stays with you when three things are already true. You can dig it by hand, you can set a fall with a tape, and the outfall is already allowed to take the water. Growtivation’s sequence uses about a 1% fall, 10 mm of drop for every metre. An 8 m run is about 80 mm lower at the outfall than at the top. Aim that fall away from the house.

The order in the hole is fabric, clean stone, pipe, more stone, then the fabric closed over the top. How to lay drainage fleece follows public install notes, and those notes do not share one overlap. Draintex specifies a minimum of 300 mm on its trench sheet. A UK review of an artificial-grass job in this set used at least 150 mm, and crate notes elsewhere use 150 mm or about 200 mm. Follow the figure for the system you are building, and lap the upstream sheet over the downstream sheet.

You can still buy that fabric. In this amazon.co.uk set the top pick for a short narrow trench is the Spudulica 1.1 m by 8 m cut, 8.8 m² of stated 100 gsm non-woven fleece at £29.55. One UK review describes a 300 mm clay trench, this fleece, about 20 mm rounded gravel and a perforated pipe. The average is 4.9 from 45 reviews, a small sample and not a laboratory test. About 1.1 m of width can close a 300 mm trench once both sides and a flap are counted.

What the shop sheet does not prove

Grams per square metre are a mass. Merchant guides treat about 100 gsm as a domestic starting point for drains, crate wraps and light separation. That figure is not an opening size, a flow rate or a puncture resistance, and it is not BS EN 13252 or BS 8661. None of these garden listings publish those numbers. Cover polypropylene the same day. Lotrak treats ultraviolet light as an installation exposure. Weed membrane blocks light. Drainage fleece filters. If the roll in the barrow is a weed sheet, change it before you backfill. The fork is on drainage fleece versus weed membrane. A terrarium hydro fleece is a third mismatch. It is not a garden geotextile.

Jobs that need a design

The French drain DIY limit arrives when the hole takes water from a building, or when the ground has to be proved. Approved Document H, on GOV.UK, is the English drainage document. CNC Building Control’s FAQ on an extension soakaway points to that document and to BRE Digest 365 where the area is large or the ground soaks poorly. Hiring a drainage engineer means hiring someone who will design the pit.

English notes, including CNC and a Wiltshire developer note, state soakaways at least 5 m from buildings and roads. The Wiltshire note treats unstable ground such as chalk more strictly. Scotland and Northern Ireland use their own handbooks, so that 5 m figure is not a UK-wide rule. If the garden cannot keep the clearance, ask building control or a designer before you dig.

Roof water, crates, and ring units

Roof water from an extension is a building-control soakaway in England, and the route is your local authority’s process. Plastic infiltration crates are wrapped in non-woven geotextile, with overlap and a sealed pipe entry. Concrete ring units are a different detail. BRE Digest 365, in the UNDA note used here, keeps geotextile around the granular fill and off the outside of the ring units. A crate parcel copied onto rings fights that guidance. Faces, overlap and the ring warning are on the soakaway crate wrap page.

An attenuation tank that holds water before a controlled discharge is specified by its designer, often with an impermeable geomembrane and a protective geotextile. If the drawing names a fabric, buy that fabric. A 100 gsm marketplace title is not a stand-in once the inspector, the crate supplier or the drawing has already specified something else.

Ground, plant, and services

A digger for a drain changes who should be in the garden. A shallow slot you can open with a spade is one job. A machine beside a wall, in a narrow side passage, or on ground you have not proved is another. If depth, spoil or access needs plant, treat it as a contractor job even when the fleece is ordinary. Trench support and spoil next to the house are a poor place to learn the limit.

Services in the garden are the other stop. A narrow trench can cross a water pipe or a cable. Locate them before you dig. Guessing a depth from the age of the house is not a survey. If you cannot trace the run, hand the excavation over, and ask whether the search is in the quote and what happens if a service is not where the plan says.

Clay changes the outfall. Fleece does not create fall, and it does not make a soil accept water it already sheds. A wet lawn on clay can still take a short land drain when the water has somewhere practical and permitted to go. A pit in ground that already holds water is a design problem. Standing water against the house is a reason to stop. A French drain tight to the foundations is outside the short lawn slot, even when the stone and the pipe look familiar.

What to ask before you hire

A plumber can connect a short pipe to an outfall that is already allowed to take the water. Designing a roof soakaway, proving the ground, and dealing with building control is a wider brief. Ask who designs, who excavates, and who owns the result if a trial pit will not soak. Checkatrade’s French-drain guidance points householders toward a drainage specialist and a building-control check. It is not a named firm, and it is not a price to treat as fair. This article will not invent a UK rate. Costwise’s reading is that labour and plant are most of an installed French drain, which matches the small fleece line on the drainage fleece comparison.

The written quote should name the design, the building-control route where water comes from a building, the search for services, plant, spoil and making good. It should name the outfall, what changes if the ground will not soak, and the fabric, including whether you need opening size, permeability and puncture resistance. If those lines are missing, you are still buying a hole.

A datasheet, and the fleece you can still choose

You need a datasheet when building control will assess the soakaway, vehicles will use the base, or puncture on a weak subgrade matters. BS 8661:2019 offers three profiles for basic separation and filtration, chosen from the ground and the construction. BS EN 13252:2016 sets characteristics for geotextiles in drainage. These amazon.co.uk cuts do not print CBR, opening size or flow. One listing omits gsm on the specification table, and a UK review reported a stamp that disagreed with the title, so read the piece you receive.

You can still supply a trade sheet a designer has named. Width and area for the simple job are in the drainage fleece buying guide. A lawn-trench cut is the wrong confidence once cars will sit on the base.