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 drain

The exterior drain system can be installed in different ways. The most popular of these is excavating the surrounding ground. Cleaning the foundation before installing a membrane is required. On peut, par exemple, installer la membrane Cantex et un panneau de drainage TremDrain DPI sur la fondation propre. They place a French drain below ground next to the footing, with a granular stone overlay. This approach requires a substantial excavation around the foundation and therefore generates additional cost the deeper the excavation.

Interior drain

A vapor barrier is placed on the foundation wall and a very sturdy SDI Pro compact drain is inserted under the concrete slab and on top of the footing. The drain leads to a particularly efficient MultiFlow drainage system. The drain is 7 inches high, which allows water and hydrostatic pressure to be drained in a very efficient way.

Interior drain or exterior drain, which one to choose ?

For most properties, there are a few important factors that influence the choice of an interior or exterior waterproofing system :

• Excavating cost : The installation of an exterior drain may require significant demolition work. Sometimes the balcony, terrace or landscaping are obstacles and must be dismantled to allow excavation. Of course, this can generate significant additional costs for the homeowner. One can then choose to turn to an interior drainage system.

• Space constraints : Some properties do not have enough space to allow the installation of an exterior drainage system. The Excavation work requires an adequate area for the machinery to operate. In other instances, access to the foundation is not possible. This is the case for properties with adjoining walls, such as townhouses. The interior waterproofing system is then the best solution.

• Foundation concrete : The quality of the concrete of the existing foundation also influences the choice of the interior or exterior drainage system. For example, lower quality concrete will require additional protection such as a waterproofing membrane. This will add a protective layer against water infiltration and moisture.

Inside, the installation conditions are much more constant, and the method remains the same. It is best to opt for this system in some cases, for example, after water has already come into the basement. In such a situation, walls and floors will most likely be removed to replace materials affected by water and moisture and mold growth. This is a good time to install an interior drain, as the basement will be ready to accommodate the system.

To choose the appropriate method, it is advisable to turn to an expert. They will be able to assess the conditions of the property and recommend the system that best suits your home.

How do you compare the costs ?

Of course, smaller jobs cost less. Often, it is best to choose an interior drainage system because it involves less demolition and no excavation. This prevents the homeowner from having to dismantling a terrace the landscaping or having to pay for the reconstruction.
The interior water control is an excellent choice to :
• Preserve a sidewalk, landscaping, mature tree;
• Avoid having to move a heat pump;
• Maintains the buildings parking area, the alley or the neighboring property.

However, when the interior of the basement is completely renovated, it may be that work inside is very expensive. The homeowner may prefer to avoid removing the walls and opt for an external system.

The dimensions of the foundation also have an impact on the final cost. A foundation that descends to a significant depth requires a wider and deeper excavation, thus more expensive exterior work, because there is more land to excavate. If the land does not provide enough space to accommodate the excavated dirt, additional costs will have to be provided to store and move it. This approach then requires more time and money.

In all cases, it is recommended that the landscaping and property constraints be assessed in order to make an informed decision.

Contact Bisson Expert foundation repair specialist for a professional estimate and find the best solution for your home. Click here for more information on this subject. An interesting article was written by Yves Perrier for Guide Perrier :

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