A Look at French Drain Prices
This is what professionals charge
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I’ve worked in the landscaping industry for many years and, more recently, as a project manager, so I have plenty of experience when it comes to French drains.
I’ve seen them constructed to standard where they protected homes, and I’ve also seen a few fail because they weren’t built correctly.
On this page, I’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.
- Examples I’ve seen where the costs were higher.
- 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.
- A case study of a French drain I saw fail.
- Where you can get a custom quotation.
I will also try to answer common French drain questions you may have
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. It’s filled with large gravel, a pipe, a geotextile material and is usually topped with soil or turf
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 that makes its way into a French drain will disperse into the ground, but many also have a discharge point, such as an existing soakaway or ditch.
How a French Drain is Built
I’ve worked with drainage experts over the years and have also installed French drains myself.
Here’s how I would go about installing one on a typical property:
1) I would check the ground for existing service pipes and cables.
2) I would perform a soil percolation test to see how quickly water disperses into the ground.
3) Next, I would dig out a trench to a width of around 300-600mm. The depth will depend on the specifics of the project, but most I’ve worked on have been between 500mm-800mm.
4) Now it’s time for me to line the trench with a geotextile filtration fabric to block most of the silt and other debris.
5) In the base of the trench, I would place a perforated pipe with rodding access points at convenient locations. To protect the perforated pipe from silt ingress, I would wrap it in geotextile fabric as well.
6) Next up, I would fill the trench with washed angular gravel around 2-4cm in size, leaving space at the top for topsoil.
7) Finally, I would wrap the top of the geotextile fabric around the top of the trench, fill the top with soil and turf over to finish.
The depth and width of the trench, the size of the perforated pipe, the fall ratio and the distance from any walls (esp old walls with shallow foundations) will depend on the project’s circumstances, hence why it’s best to get professional advice.
How Much Does a French Drain Cost?
As a project manager, I’ve previously worked with firms that built French drains.
However, for domestic projects, the pricing is often different and it’s difficult to pin down a figure as every project is different.
However, to get an idea of how much firms are currently charging, I contacted 11 landscape gardeners and drainage firms in the UK and asked for prices to install a basic French drain – I supplied them with photos and percolation test results.
The prices below are per linear metre, include VAT and are based on the prices I 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.
I’ve worked on projects that were far more complex and hard surfaces such as patios, paths etc., had to be dug up and made good afterwards. Also, 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. I’ve found that in some cases, the cost of making good the ground can exceed the cost of the French drain.
I’ve also worked on projects where we needed to install a soakaway, expand ditches and improve or create drainage solutions at the discharge point, and this added to the cost.
French Drain Material Prices (Per Linear Metre)
As part of my independent research into French drain costs, I looked at the price of the materials and calculated a figure per linear metre.
You may find this helpful if you are considering building a French drain DIY or want insights into how much a project like this will cost.
What Type of Tradespeople Can Construct French Drains?
I’ve worked with both landscape gardeners and drainage firms, and both are usually able to construct French drains.
In my experience, landscape gardeners often charge less than specialist drainage firms, and sometimes by a significant amount.
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.
I only have limited 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 by Experts
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.
Q) Where does a French drain discharge?
A) As French drains consist of a trench, often 0.3m+ 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.
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 dwellings and old walls with shallow foundatations, should be designed by an expert and completed by a competent person.
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.
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.
An engineering consultant or similar can provide reliable figures for suitable pipe sizes if your project is complex.
A two-pipe trench, without geotextile fabric.
I’ve Seen Two French Drains Fail – Here’s What Happened
The first time I saw a French drain fail was back in 2011 when the customer reported water pooling on their patio. They had recently purchased the property and the survey had highlighted a French drain in the garden with a discharge point into a nearby ditch just outside the property boundary.
My team and I at the time inspected the pipe from the discharge point with a camera and saw the pipe was blocked.
We dug up the trench and could see that the pipe wasn’t wrapped in geotextile fabric and neither was the trench.
We rebuilt the French drain and bought it up to standard with an access rodding point and geotextile fabric material to prevent dirt ingress.
The second time I’ve seen one fail was a few years ago, it appeared to be built to standard, but the gravel hadn’t been washed, and the fine sand had clogged the perforated pipe, which also laid too shallow for the sand to wash away.
The team I was overseeing excavated the French drain and rebuilt it using larger washed gravel and new geotextile fabric around the pipe, which was laid on a steeper gradient, an access point was also created to allow for rodding in the future.
(Notes: Access points for French drains are quite rare and aren’t required by the Building Regulations, but for the long drains I’ve worked on, I feel they are beneficial and worth the extra cost).
Our Experience with French Drain Construction
The author of this guide, Daniel, has personally built two French drains and overseen the construction of several more in his role as a project manager in the landscaping business.
The prices on this page are based on:
- Quotes we received from 11 landscape firms he contacted.
- His experience of purchasing materials, hiring equipment and doing the work himself.
Author: Daniel Woodley
In his spare time, Daniel enjoys gardening, hiking and scrambling. He frequently posts videos to his popular YouTube Channel and is well known in the hiking community.
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