French Drain Prices

For thousands of years, humans have dug ditches to divert rainwater away from land and property, often to protect crops and homes.

A French drain is a similar concept except that the rainwater is collected and transported underground where it can seep away.

Early French drains were nothing more than trenches filled with rocks and gravel and overlaid with soil.

Modern French drains are trenches filled with beach gravel and plastic perforated pipe, all wrapped in a piece of fabric to prevent roots, soil and other contaminants from blocking the drain. Many have rodding points so they can be easily cleared of blockages.

Page Contents

On this page, we’ll cover:

• What a French drain is and what it does.
• How much professionals charge per metre to install a French drain in a typical garden.
• Example of where the costs may rise.
• A list of materials priced per metre (perfect for you DIYers out there).
• Professional design costs and the potential repercussions of installing a French drain incorrectly.
• Where you can get a custom quotation.

We will also try to answer common French drain questions.

What is a French Drain and What Does it Do?

A french drain is a narrow trench, often no more than 300mm wide and of variable depth.

A filtration fabric that’s manufactured to allow water through but to keep silt and particles out is then laid inside the trench, and a layer of gravel is then laid across the base of the trench.

A perforated pipe, typically 80-200mm wide, is then laid, and the entire trench is filled with more gravel to just below the surface.

The fabric is then wrapped over the top of the trench to fully enclose the pipe and gravel. Soil, grass, or other top layer is then put into place, hiding the drain.

French drains are often located next to dwellings at the bottom of sloping ground, their purpose is to catch the excess surface water and move it away from the property so it can’t damage the foundations.

Much of the rainwater will disperse into the ground via the French drain but many also have a discharge point such as an existing soakaway or ditch.

How Much Does a French Drain Cost?

We contacted 12 landscape gardeners and drainage firms in the UK and asked for prices to install a basic French drain.

The prices below are per linear metre, include VAT and are based on the prices we received from the firms.

Additional Drain Costs

The prices in the table above assume ideal conditions where a drain can be excavated in an open garden.

Expect to pay more if any hard surfaces such as patios, paths etc., need to be dug up and made good afterwards. French drains are often located close to the property where there are lots of concrete, patios, paths and driveways etc., in addition to the soil. The drainage pipes from these hard surfaces may need to discharge into the French drain, complicating the project.

If you need to install a soakaway, ditch or other drainage solution at the discharge point, this will add to the cost.

French Drain Material Prices (Per Linear Metre)

This is how much the materials used in the construction of a French drain cost per linear metre.

This is helpful if you are considering building a French drain DIY or just want insights into how much a project like this will cost.

What Type of Tradespeople Can Construct French Drains?

Landscape gardeners and drainage firms normally construct French drains and both normally have the experience to undertake this type of work.

Who Can Design French Drains? How Much Do They Charge?

Simple, basic French drains can be designed by landscaping and drainage firms for a nominal fee. However, more complex projects, especially those involving more than one property or those that could potentially affect a neighbouring property, should be designed by an engineering consultant or similarly skilled person.

We don’t have much experience working with engineering consultants on French drains, but a firm with the qualifications wrote this article, and their prices start at £950+VAT for a single dwelling.

5 Frequently Asked Questions – Answered

Q) How does a French drain differ from a regular drain?

A) A French drain is designed to capture rainwater from a wide area and transport it along the perforated pipe where it can seep into the ground, it may or may not have a discharge point. A regular drain collects water from single inlets such as roof gutters, drains in patios, driveways etc. and transports the water in a sealed pipe to a discharge point which is usually a ditch or soakaway.

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Q) Where does a French drain discharge?

A) As French drains consist of a trench, often 0.5m+ deep, they can hold a lot of water which will gradually seep into the ground. Therefore, they may have a discharge point at the end of the trench, but not always. Discharge points could be underground soakaways, existing rainwater drains or existing ditches.

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Q) Can a simple French drain be constructed DIY?

A) Yes, most simple French drains are easy to construct, but one should consider the repercussions of making mistakes (flooding, subsidence, insurance validity, legal consequences etc.). Complex drainage solutions, including those that span more than one property, or are very close to a dwelling, should be designed by an expert and completed by a competent person.

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Q) How long does a French drain last?

A) Old French drains that were only filled with gravel and rocks lasted one or two decades before they needed to be cleaned and rebuilt. Modern drains with perforated pipe, geotextile filtration fabric and gravel should last the life of the property.

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Q) What size pipe should I use?

A) The drain’s designer should decide on the size of the pipe, the trench and the gradient of the pipe by completing a complex calculation that takes into account:

• The surface area, its type, size etc.
• The permeability of the ground.
• The expected rainfall for the region.

Only an engineering consultant or similar can provide reliable figures for suitable pipe sizes.

A single pipe French drain and geotextile fabric next to a highway. Photo by Edisteew | Img Licence

Further Reading

Our lawn care guide contains over a dozen helpful articles including:

• How to grown grass in a shaded garden.
• Get rid of moss without blackening your lawn with this product.
• The best grass seed for the UK climate.
• Lawn fertilisers that actually work, as tested by us.

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