Find out about the differences between interior and exterior waterproofing drain systems. Compare the benefits, costs and installation methods
Find out what you need to know
You own a home and need to protect your basement from water infiltration and moisture ? It’s not easy to navigate between the various waterproofing systems on the market. To get a clearer picture, Bisson Expert shares its expertise so that you can find the right solution for your property.
What are the options: interior or exterior drains ?
There are two types of approaches to keeping the basement of your home dry : one can opt for an interior drain system or an exterior drain system. Both drainage systems are recognized as being effective, but it remains essential to understand their differences. Each property is unique and requires an appropriate drainage solution.
The two systems are just as efficient and allow water to be drained efficiently from the foundations. Even if they perform the same functions, the technologies are applied differently and require special installation techniques.
Exterior drain
Exterior waterproofing drain system are historically more common in Quebec. This approach involves excavating the ground outside near the foundation to install a French drain. Excavation sometimes requires significant demolition work to free up space to access the foundation. We can only install the drains during the summer, the autumn and spring. It is therefore not recommended to install such a system when the ground is frozen. Therefore, limiting the periods that the work can be completed.
Interior drain
The interior water control drain system has been available in the U.S. market since the 1990s. This relatively new technology is currently gaining popularity in Quebec, and for good reason. Perfectly adapted to our climatic conditions, the approach from the inside is to insert a drain under the existing concrete slab of the foundation. This is an ideal solution, especially for houses whose foundations are difficult to access.
The interior and exterior drain systems are therefore differentiated mainly by the installation method and the cost. For example, it is possible to install the interior waterproofing drain 12 months a year. The work is therefore not limited to a specific time of year.
Installation methods
Exterior French Drain
The exterior drain system can be installed in different ways. The most common method involves excavating, then cleaning the foundation before applying a membrane. For example, the red polyurea membrane is sprayed directly onto the clean foundation to create a seamless waterproof barrier. A French drain is then placed below ground level, covered with granular stone, ensuring optimal water management around the foundation.
Interior French Drain
The interior drain system is installed directly beneath the basement slab. After opening a trench along the foundation walls, a drain is laid at the footing of the foundation and connected to a catch basin equipped with a sump pump. The system is then covered with crushed stone and sealed with a concrete finish leveled to the existing slab, providing effective waterproofing from the inside.
Interior drain or exterior drain, which one to choose ?
The choice between an interior or exterior waterproofing system depends on several factors related to your property:
- Cost and accessibility of excavation
Installing an exterior drain may sometimes require significant preparatory work (removing a balcony, terrace, or landscaping, limited access for machinery, etc.). When these constraints are present, interior drainage becomes an alternative to consider.
- Space constraints
In some properties, the space required for excavation is not available, as is often the case for townhouses with shared walls. In such cases, interior drainage can protect the foundation despite these limitations.
- Quality of the foundation concrete
The condition of the concrete also influences the choice of system. Lower-quality concrete will be better protected by a membrane applied on the exterior. At Bisson Expert, we use the red polyurea lining, recognized as the best waterproofing membrane on the market.
Both approaches provide effective and long-lasting protection. Our experts will evaluate the specific conditions of your property and recommend the most appropriate method, whether it’s an interior or exterior system.
How do you compare the costs ?
Of course, the scope of the work influences the cost. In some cases, an interior drainage system may be preferred, as it avoids full excavation of the property and allows certain elements, such as a sidewalk, terrace, mature tree, or heat pump, to remain in place.
Exterior drainage, on the other hand, remains a solid and proven solution, especially when the basement interior is already finished or renovated. This approach also makes it possible to apply a protective membrane to the concrete, such as the red polyurea membrane, recognized as the best waterproofing membrane on the market.
The depth and dimensions of the foundation can also influence the choice, as they determine the scale of excavation work required.
In all cases, the best decision is based on a complete assessment of the property’s layout and constraints. Our experts will recommend the solution best suited to your situation, whether it involves interior or exterior drainage.