Are the basements endangered in new constructions?
Although the existing basements are there to stay there, houses on slab, without basement, are starting to multiply in the real estate landscape, especially since the last deluge, on August 9, 2024, while the storm Debby had poured 157 mm of water to Montreal-Trudeau airport and more than 180 mm in the Laurentians and Lanaudière in a few hours.
Met on the site of a single-family house in Varennes, in Montérégie, where the owner has caused a concrete slab for his residence which will have no basement, the entrepreneur Pascal Dubé says that construction on slab “is less and less rare. With the floods of August, last year, there is no problem with a slab. »»
Always problems
“The basement is not to know which one will flow or if it will flow, it is when it is going to flow,” he continues. It is sure that a basement flows one day. Of course there will be a crack, it is sure that there will be an infiltration of water. We are always renovating basements because they are wet, they are moldy, they have infiltrations, there are cracks, there are cracks. There are problems with the basements all the time. »»
“It is true that construction on slab is more and more frequent,” confirms Marco Lasalle, director of technical services to the Association of Professionals under Quebec Housing Construction (APCHQ). He explains that the inhabited subsoil is a peculiarity of northeast America, especially in Quebec, Ontario and New England. “At the start, when the French built the houses directly on the floor and it was cold, it was not super comfortable. At one point, the English showed us to dig and put a wooden floor over it. There, we no longer slept on a block of ice. We decided to put our potatoes in there to spend the winter and all that. And at one point, we decided to dig them by saying that it is square foot easily convertible. »»
Like Pascal Dubé, he emphasizes that the problems of a building are much less often attributable to the external walls or the roof than in the basement and that it is “always work that costs quite expensive. Repeating a foundation drain, we are easily $ 250 on the linear foot. With everything that follows: redo the paving, redo the bedbags, all that ”.
A more ecological approach
“People who have experienced floods, who are not the first buyers, really see the interest of not having this anxiety of having a basement which is likely to flood, either by surface waters or sewer repressions,” explains Emmanuel Cosgrove, director of ecohabitation, an OBNL whose mission is to promote the most ecological approach possible during the construction or renovation of a house. The organization has long advocated the construction on slab “especially when you create a small elevation of about one foot of the floor around the house, which is mounted on a small hill. Here we have a house at a very low risk of flood ”.
The slab construction must still make its way through preconceived ideas, he admits. “There are many entrepreneurs who believe that the basement is integrated into the code (of the building) and that it is compulsory, while it is false. There are a lot of false perceptions of the slabs on ground which are the most common foundation and by far elsewhere in the world. Digging under the ground level exposes us to several risk of gas from the soils such as the radon, but especially to risks of humidity and flood and as it is a very recurring theme these days, flooded subsoils, disjointed properties for the risks linked to water, people who build nine look towards alternatives and often they come across the solution of the slab which has been promoting for more than 20 years. »»
The interest in eco -phabitation greatly exceeds flooding or radon issues. “Concrete,” explains Mr. Cosgrove, is by far the material that emits the most greenhouse gas throughout the construction industry. Not to build a basement can reduce up to 60 % the amount of concrete required and, by extension, up to 40 % the carbon footprint of the construction of a house.
Back to the sanitary video
Marco Lasalle, however, makes an important reserve in the face of slab construction. “It is not a situation” one size fits all “. For example, if I don’t have a basement and I am on the edge of a river that can overflow, I don’t help myself. I have just aggravated my misfortune because if the river overflows, it is not a basement that will be flooded, it is all my ground floor. Kitchen, bathroom, all the living space. »»
But will the basement be flooded? “It is not a good idea either to go make a basement in the flood zone. I could rather do what was at the time, a crawl space, a free space under the floor of the ground floor where, if there is water, it will just be rock or earth that will be wet. We can store things that are not afraid of water, like a kayak, but we do not want to arrange it. If the river comes out of her bed, she will go into the crawl space. »»
In urban areas, however, the portrait is different. “With the floods, the rainfall sewer systems of municipalities no longer provide. Precipitation is too large over a short period, the sewer is not able to take it and there, there are repressions and a backward repression, it is always in the basement and very rarely on the ground floor. If there is no basement, there is no backdrop of sewer. If it goes to the ground floor, it is the whole street that is flooded. Possible but unlikely. »»
The less necessary basements?
Pascal Dubé, he has no illusions. He may be built in the agricultural zone, far from any river and rain sewers, his client would not be immune with a basement. For what ? Because last year, he built his own house on the other side of the street and has a basement. “I was flooded on August 9. I was doing the basement, I had a new drain, a new anti-return valve, but it mounted. Because at one point, when the ground is full, it goes up around the pipes in the ground and it comes out. »»
Knowing this, why did he build one? He looks at the concrete slab on which he is and replied: “If I had been able to do that, I would have done it, but with three children I needed a basement. Here they only have a child, ”he drops.
And that too is one of the new realities likely to promote construction on slab, explains Marco Lasalle. “We are fewer and fewer in houses. We need less basements. Before, in a house, we were a family of four. Now each family has two houses with separations. We may less need the basements, except to tighten old books and things that will feel moldy. »»
Costs and savings
Is there a salvation for existing basements? Yes, if you are ready to get deep into its pockets, says Emmanuel Cosgrove. “Even new houses have no waterproofed foundations. A basement that limits the risk of infiltration will cost tens of thousands of dollars more. So, it is rarely something that is asked of the entrepreneur in a submission. »»
He argues that the money saved by pouring a slab rather than making a basement can be transferred to the rest of the house and he hopes “that insurers will follow with discounts, for example, for houses on slab, given their innate resilience. Because if we limit the risk of flooding, we should be covered, but without paying the price of someone who is at high risk with a basement that is not waterproof. »»
