French drain

Protect your foundations against water infiltration and moisture with Fondabec

Clay soils, iron-rich ochre, heavy rainfall, and freeze/thaw cycles make foundations particularly vulnerable to water infiltration in Quebec. A French drain, also known as a foundation drain, is a system designed to divert water away from foundations, thereby preventing cracks, infiltration, and subsidence.

At Fondabec, we operate throughout Quebec to install, inspect, and replace French drains using proven methods adapted to the conditions of your property.

What is the purpose of a French drain?

A preventive and corrective role

The main function of a French drain is to channel groundwater away from the foundation footings. When properly installed, it protects the structure against:

Types of French drains

Not all French drains or foundation drains meet the same needs. Over time, several types of materials have been used to drain foundations. Some, such as agricultural or terracotta drains, are now considered obsolete or even non-compliant with current standards.

BNQ drain: this is the current standard recommended in Quebec. It is a perforated polyethylene drainage pipe (often 4 inches in diameter).
Agricultural drain: commonly used in the 1980s and 1990s, this type of drain is often the cause of infiltration problems today. It crushes easily, is not surrounded by geotextile, and clogs quickly, especially in the presence of ferrous ochre.
Terracotta drain: very common before 1970, this drain is made up of short sections of ceramic or clay glued end to end. Fragile and not watertight, these drains crack, shift over time, and allow fine particles to enter, which can clog them.
Interior drain: this is a recommended solution when exterior access is very limited or even impossible (semi-detached house, restricted land, winter work). This system is installed inside the perimeter of the basement, under the concrete slab. It is connected to a sump pump and a collection basin to facilitate water drainage.

At Fondabec, we only install compliant drains (e.g., BNQ-type drains) that are designed to last.

Signs that your French drain is clogged or ineffective

When drainage problems arise, symptoms often appear gradually, both inside and outside the building. It is therefore important to recognize them quickly to prevent water infiltration, mold, or even structural damage. Here are the main signs that may indicate that replacement or inspection is necessary.

Inside the house

Outside the house

What causes a French drain to become clogged or ineffective?

A French drain (if already installed) can lose its effectiveness for several reasons, often related to the age of the installation, soil conditions, or poor maintenance. Identifying the cause allows you to choose the right solution: cleaning, repair, or complete replacement.

Ferrous ochre:
enemy number one in Quebec

Very common in the clay soils of the Montreal area, ferrous ochre is an orange-colored sludge composed of iron and bacteria that forms when it comes into contact with groundwater. It can quickly clog a drain, even a new one, if an adequate filter membrane is not used.

Age or subsidence of the system

A French drain installed more than 25 years ago (especially one made of clay or without protection) is often at the end of its life. Subsidence of the soil around the foundation can also deform or break the drain, especially in the case of clay or poorly compacted soil.

Accumulation of debris and fine particles

Over time, soil particles, roots, sand, or gravel can infiltrate the drain if the geomembrane is damaged or improperly installed. This causes a slowdown in flow, followed by complete blockage.

Heavy rains and snowmelt

In Quebec, even a functional drain can be put to the test during extreme weather events. Heavy rains in the spring or fall, as well as rapid snowmelt, saturate the soil deep down. If the drain is partially clogged, poorly ventilated, or has insufficient slope, it may not be able to drain water in time, causing problems with the structure of buildings.

No drainage system

Some properties, particularly houses built before the 1960s, have never had a French drain installed, or have an old system that is now completely obsolete. Without a drainage system, groundwater or runoff accumulates directly against the foundation walls, increasing hydrostatic pressure and the risk of infiltration.

Insufficient drainage slope

If the drain has not been installed with the minimum required slope, water may stagnate rather than flow toward the sump or sewer. This accelerates the formation of blockages and promotes infiltration.

How Does a French drain replacement or installation work?

Having a French drain installed or replaced is a technical operation that requires expertise, rigour and adherence to current standards. At Fondabec, each intervention is carefully planned to minimise the impact on your property and to guarantee the durability of the system. Whether for new construction, a preventive replacement or an emergency intervention in the event of infiltration, our team adapts to site constraints (accessibility, soil, season, neighbours) to offer a tailor‑made solution. Here are the typical steps in replacing a French drain, both outside and inside.

Exterior French drain installation or replacement

Replacing an exterior French drain involves a full excavation around the foundations. Here are the main steps followed by the Fondabec team:

Excavation down to the footing at the base of the foundation
Cleaning the foundation and inspecting visible cracks
Installing a BNQ‑compliant perforated drain on a bed of clean stone
Adding a geotextile membrane to prevent fine particles from entering
Connecting to the sump or drainage network (e.g. storm sewer)
Backfilling with draining materials
Final grading of the terrain and landscaping restoration if required

Interior French drain installation or replacement

When exterior excavation is impossible (shared lot line, limited space, winter work), installing an interior drain is an excellent alternative:

Cutting the basement’s concrete slab near the walls
Excavating a trench to lay the perforated drain
Adding a filtering geotextile and a bed of clean stone
Connecting to a sump pump and collection basin
Recasting the slab and finishing with concrete

Foundation Waterproofing: an essential complementary protection

Even the most efficient drain alone is not always enough to protect your building against infiltration. This is why Fondabec recommends adding complete waterproofing of the foundation, especially during an exterior replacement.

Why Combine Drainage and Waterproofing?

A good drainage system carries water away, while the membrane prevents water from touching the foundation. Together, they offer optimal protection against:

This combination is often required by insurers or municipal grant programmes during major renovations.

Waterproofing membrane applied to the foundation

After cleaning the foundation, we apply an elastomeric waterproofing membrane, often combined with a rigid or dimpled drainage panel (such as Delta‑MS). This solution:

Comprehensive support with Fondabec

Assessment and Camera inspection

Each project starts with an on‑site evaluation, including a visual inspection and camera inspection of your French drain to determine the origin of the problem (blockages, cracks). We then perform an infiltration test to evaluate your drain’s ability to evacuate water.

Finally, our certified experts provide you with a clear report, outlining the solution to be implemented (partial repair or complete replacement depending on the condition of your installation) along with a detailed estimate.

Grants and Subsidies

Installing or replacing a French drain can be partly subsidised by government programmes (e.g. the federal Greener Homes grant, Rénoclimat in Quebec) and/or municipal subsidies (e.g. Renoplex in Montreal) to help you complete the work.

We can guide you through finding aid and subsidy programmes that suit your situation.

Need a French drain service?

For more than 20 years, Fondabec has been assisting homeowners in Greater Montreal and across Quebec with their French drain inspection, replacement or installation projects. Whether you’re in Laval, Longueuil, Terrebonne, the North Shore, the South Shore or elsewhere in the region, our team travels quickly to assess your situation and propose the most durable solution.

We hold all the certifications required in excavation, civil engineering and underpinning, and we work with engineers and surveyors to guarantee the compliance and quality of each project.

Fill out this form or call us today!

FAQ

How much does a French drain replacement cost?

The price of installing or replacing a French drain depends on several factors including site accessibility, whether the work is done indoors or outdoors, the depth of the foundations, the presence of iron ochre, and the type of membrane used.

Can the work be done in winter?

Yes, under certain conditions this work can be carried out at that time of year. Excavation is more complex, but our teams can intervene if the site is clear.

Can a drain be replaced without excavation?

Unfortunately, a complete replacement requires excavation around the foundation. However, a camera inspection can be carried out without excavation.

How long do the works take?

The duration depends on the nature of the project, site accessibility and soil conditions. On average, installing or replacing a French drain for a single‑family home takes between four and seven days. A larger building or more complex intervention may take longer. A precise estimate is provided during the initial evaluation.

Do you offer warranties?

Yes, our work is covered by a warranty ranging from ten to twenty‑five years, depending on the type of installation.

For over 20 years, Fondabec has been assisting homeowners in Greater Montreal and throughout Quebec with their excavation projects.

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