Montreal flooding: Why one builder thinks we shouldn't have basements

Numerous homes across the Greater Montreal Area experienced some level of flooding after the heavy rain last week.

André Gagné, a professional building inspector and expert in building construction, gives a few tips on how people can prevent a major disaster.

CTV News: Are basements too much of a risk when it comes to flooding these days?

Gagné: If we go back a few years, many years ago, a basement was used only for storage.

Over the years, probably around the 1960s, people started to develop the basement: playrooms, bathrooms, for the kids who are growing, so that's the time we started to use the basement for a living space.

But the technical methods for building basements didn't change.

We are building basements the same way we built back in 1960s: concrete walls, French drain around the foundation, maybe a sewer system by gravity or maybe the water goes in a sump pump.

CTV News: What do you think is the best solution?

Gagné: It is my own opinion that we should not build houses using the basement for living space.

[But] if you're losing the living space in the basement, we have to find another place to build rooms, bathrooms etc.

So, for example, back in the 1960s, we had bungalows with 100 square metres.

Most of the time, you have the same area in the basement, so almost 100 square metres.

If you remove the basement living space, how [do we] have the same area for storage, for a second bedroom, the third room?

The Régie du bâtiment [du Québec] should write a regulation: "do not permit a basement with a living space."

You could use the basement for storage or a crawl space, but we should [not] use the basement for a living space.

CTV News: But could we adjust the way these basements are built?

Gagné: We could build a basement like a boat, so that's a completely watertight basement, but that would cost about three times the actual cost.

CTV News: It seems like people still want to have a basement. What about different pumping systems?

Gagné: A standard foundation has a French drain around the footing at the bottom of the foundation, and normally, they collect the water around the foundation to go to a sump pump pit.

Sometimes, it's going by gravity to the sewer system of the city.

But if you have a backwater valve and the pressure is so high in the sewer system, then the flip trap closes, so the water coming from the French drain won't be able to reach the sewer system.

The best way is to add another sump pump, not necessarily connected to the sewer system, but just to throw the water on the ground outside, so that will prevent flooding.

The other way we have to think is what kind of material we are using when we are rebuilding the basement.

Most people still use floating floors to cover the concrete basement slab, and they use standard gypsum board for the wall sealing.

But there is some gypsum board without any paper because standard gypsum with paper on both sides will suck the water humidity, and it creates a lot of moisture on the walls.

To cover the concrete slab, you can use ceramic tiles, so if there's water, that would be easier to clean it.

CTV News: How dependent are homes on municipal sewer systems and aqueduct systems when it comes to flooding and getting rid of water?

Gagné: Most of the houses built in major cities, depending on the sewer system, most of them, I would say, 95 per cent or 98 per cent, the plumbing code asks the builders to connect the French drain to a sewer system to the municipality with a backwater valve.

This is the only protection we have.

In the future, municipalities could ask the builders to install independent pump systems so if the backwater valve is closed, the pump will act and evacuate the water.

The sewer system for the municipality is not designed to receive that amount of water in a really short period.

CTV News: Is there something people should know about their basements when it comes to insurance?

Gagné: You have to look at your insurance company contract because most of the insurance companies do not offer protection against mould in the basement.

You better check with your insurer to be sure that you're protected against flooding.

-- Answers have been shortened for clarity.