Introduction
In Quebec, many homes and chalets are built on sloped lots. While they offer stunning views, they also bring a major challenge: managing rainwater and surface runoff.
Without proper measures, water can:
- Accumulate behind retaining walls or foundations,
- Increase hydrostatic pressures,
- Cause slope erosion,
- Endanger septic systems upstream or downstream,
- Impact neighboring properties.
In fact, many municipalities now require a stormwater management plan for construction on sloped lots or near sensitive areas.
Risks of Building on a Slope
1️⃣ Water buildup behind retaining walls or foundations
2️⃣ Accelerated soil erosion during heavy rainfall.
3️⃣ Pressure on septic systems
4️⃣ Uncontrolled water transfer to neighbors
5️⃣ Regulatory non-compliance if no drainage plan is provided
Common Engineering Solutions
1. Interception Trench
A drainage trench placed upstream of the building or retaining wall captures slope runoff and redirects it to a safe outlet (such as a municipal ditch, retention basin, or vegetated swale).
2. French Drains
Perforated pipes surrounded by clean stone can be installed:
- Around house foundations to control humidity,
- At the base of retaining walls to relieve hydrostatic pressure. They allow water to flow out by gravity.
3. Roof Water Management
Gutters and downspouts should be connected to sealed pipes that discharge into a retention basin or vegetated swale. This prevents uncontrolled water accumulation near the foundation.
4. Retention Basin
A temporary basin, sized according to local rainfall, retains stormwater and gradually infiltrates it into the ground. Excess water is safely released to a municipal ditch or designated outlet.
5. Swales and Check-Dams
Vegetated swales slow down water movement and promote infiltration. Small stone or wooden barriers (check-dams) can be added to reduce velocity and minimize erosion.
Why It Matters
A proper runoff management plan ensures:
✔️ Protection of the house and retaining walls
✔️ Safety of septic systems
✔️ Preservation of neighboring properties
✔️ Compliance with municipal regulations
✔️ Long-term durability of the site
Conclusion
Building on a sloped lot requires careful water management engineering. It’s a regulatory requirement in many municipalities — and a crucial investment to protect your project.
👷♂️ At Florcon, we design drainage and runoff management plans that meet municipal requirements and adapt to each site’s conditions.
📞 Planning to build on a slope? Contact us today for a compliant and sustainable solution.
Building on a Sloped Lot: How to Manage Surface Runoff