Exterior French Drain
Installation, repair and replacement of foundation drain with excavation and waterproofing in Montreal and South Shore
A French drain (also called foundation drain) serves to capture and evacuate water at the base of foundation walls to reduce water pressure around the house and limit risks of water infiltration, basement humidity, mold, and foundation deterioration.
Archi-Maitre Excavation offers complete exterior French drain service only: new drain installation, repair of damaged sections, complete foundation drain replacement, and foundation waterproofing during work.
Common French Drain Problems
Clogged Drain
Sediments, fines, deposits and drainage backfill clogging reduce drainage efficiency.
Iron Ochre
Can contribute to clogging the system. APCHQ recommends prevention/maintenance measures.
Crushed or Broken Drain
Some sections stop draining, water stagnates near foundations.
Improperly Installed Drain
Inadequate level, slope or coating: a poorly positioned drain loses a lot of efficiency.
Insufficient Surface Drainage
If water is directed toward the house (negative slope), you increase water load on foundations.
Backfill Settlement
Poor compaction or inadequate materials cause settlement and malfunctions.
Signs of a Defective French Drain
How to quickly know if your French drain needs to be repaired or replaced:
When these signs are present, an on-site assessment is recommended to confirm the cause and determine if targeted repair is possible or if complete replacement is necessary.
What Standards Require
Quebec Construction Code (Part 9)
The GCR/RBQ sheet explains Part 9 Code requirements for drainage at bottom of foundation walls, particularly when footings are below frost penetration level.
APCHQ reminds that pipes/drains used for foundation drainage must be at least 100 mm (4 in) in diameter.
An ACQ technical sheet on waterproofing/drainage cites obligation to provide drainage system at base of exterior walls (except provided exceptions).
A well-done exterior French drain = proper level, proper material, proper drainage coating, protection/filtration, and adequate evacuation.
Our Method
(Archi-Maitre)
Installation, repair or replacement of exterior French drain
1. Building and Site Assessment
Analysis of access, site slope, low points, foundation type, observed symptoms, and site constraints (porch, entrance, landscaping, neighborhood).
2. Locating Before Excavation (Safety)
Locating request via Info-Excavation to know location of underground infrastructures and avoid dangerous and costly breaks.
3. Perimeter Excavation to Required Level
Controlled excavation all around (or on targeted sections), to foundation base / footing as applicable.
4. Wall Preparation and Waterproofing
Cleaning, repairs as needed, then installation of waterproofing membrane and appropriate protections before backfilling.
5. Drain Installation and Drainage Restoration
Drain installation (compliant diameter), placement of drainage materials and protective layers. Municipal documentation (e.g. Longueuil) specifies coating and inspection elements before backfilling.
6. Backfilling, Compaction and Finishing
Careful backfilling + compaction, then site restoration. Surface drainage optimization (slope) to move water away from foundation.
Permits and Local Requirements
Montreal:
The City of Montreal indicates that to install or replace a French drain, an excavation permit may be necessary.
South Shore:
Rules vary depending on type of intervention and context (public domain occupation, excavation near infrastructures, etc.). We always validate according to municipality.
Frequently Asked Questions
Do you only do exterior French drain?
Yes. Our work is done by excavation on the exterior, around the foundations.
Repair or complete replacement: how to decide?
It depends on the situation: drain age, general condition, damaged sections, presence of obstruction, and overall system efficiency. After on-site assessment, we recommend the most durable solution (targeted repair if possible, replacement if system is at end of life).
What are the most frequent signs of a clogged or ineffective drain?
Infiltration after rain, persistent humidity, musty smell, water stains and efflorescence at bottom of walls, worsening cracks and localized damp areas.
Can iron ochre cause problems?
Yes, it can contribute to clogging the drainage. APCHQ discusses prevention/maintenance and notably mentions the interest of cleaning chimneys to facilitate maintenance.
Does surface drainage really matter?
Yes. APCHQ recommends landscaping the site to move water away from foundations (positive slope). Adequate surface drainage significantly reduces water load on French drain.
Is a permit required in Montreal?
Montreal indicates that an excavation permit may be required, including for installing/replacing a French drain. We take care of verifying requirements according to your area.
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