Protecting your basement from flooding

It’s inevitable: heavy rainfall will continue to cause damage to Quebec basements, as was the case this summer. Without having to start from scratch and rebuild everything at great expense, are there affordable adjustments that can be made to our properties? Marco Lasalle, technical director of the Association des professionnels de la construction et de l’habitation du Québec (APCHQ), is a good source of advice for those who want to limit water ingress and its consequences.

Small slope, big difference

A ground is never perfectly level. Rainwater or melted snow will inevitably flow in one direction. “What we want is for it to move away from the foundations. Around the entire perimeter of the building, we can simply add a slope, without it necessarily being very steep,” recommends Marco Lasalle. All you need to do is slightly raise the ground of the surrounding land and let the grass grow back.

Gutter, go shake yourself further

Just as we seek to repel rainwater, it would be wise to direct the flow coming from gutters away from the foundations. “In any hardware store, you will find gutter extensions and even flexible pipes that unroll under the pressure of the water, then roll up on themselves again once the heavy rain has passed,” says Mr. Lasalle. We will ensure that this water is discharged a little further onto our land, at a distance of 4 to 6 feet, or approximately 1.2 to 2 metres.

A welcome diversion

The APCHQ receives a lot of calls from homeowners who think their drain is faulty. However, it works. The problem is that the municipal sewers are full to the brim and can’t take in any more. “In this case, we need a bypass. When the city sewer is full, the water from the residential drain will spill outside onto the property. We’re talking about a $25 pipe and a minimum call to a plumber,” emphasizes the association’s technical director. To transport the water, you need a sump pump (a good investment, according to Mr. Lasalle), or even several pumping units. In addition, a backup battery is very useful in the event of a power outage, a common situation during terrible weather.

Block arrivals

It is rare that one is shocked: violent storms and torrential rains are often announced in advance. When this is the case, Marco Lasalle encourages taking the lead by temporarily blocking all elements of the basement connected to the plumbing (toilet, floor drain, sink, shower, etc.) and which could lead to backflows. The lethal weapon? A simple rag to obstruct the drains – without exaggerating, at the risk of clogging them – on which one adds a little weight to resist any possible hydraulic pressure. There is no need to block the drains on the ground floor and on the upper floors, only those in the basement are concerned.

Suitable materials

For the technical director of the APCHQ, building below ground level in the same way as above the property line is a mistake. It is very fashionable, but home theaters, games rooms and libraries installed in the underground part are exposed to significant damage. “I recommend the least possible materials, the least organic and putrescible possible,” he insists. In his sights are, for example, floating floors made of fiberboard (MDF), which should be avoided, while vinyl surfaces, not much more expensive, will be much better suited to hydraulic exposures. Vinyl floors also have the advantage of being removable, which will greatly facilitate possible evacuations and drying. “That said, are we really obliged to put a floor covering? Can’t we keep the exposed concrete slab? Give it an epoxy finish?” asks Marco Lasalle.

For half-timbering, steel would be preferable to wood. And when the latter is difficult to avoid, it is better to favor real wood, for example for skirting boards. “For gypsum walls, I recommend leaving a minimum space of two inches from the floor to prevent moisture from rising by capillary action. There are very beautiful PVC coverings,” he suggests.

The basement to be questioned

A word of advice to those planning to start work on their house soon. It’s best to ask yourself some questions before breaking ground, and the right ones. The main recommendation from the APCHQ technical director: insulate the foundations from the outside, a proven process. “There may be water infiltration, but the insulation will not be affected because it is already in contact with moisture.” In fact, the problem is much broader: is building basements still relevant in Quebec, given the climate outlook? “It depends on the situation,” says Mr. Lasalle. “Someone who lives near a river should not build a basement. But with a slab on grade, the entire ground floor will be flooded. In these cases, we could perhaps consider crawl spaces. But generally speaking, we have big questions to ask ourselves about building basements for new buildings.”