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Basements – the below grade story

It’s usually in springtime when many people may experience problems with water seepage into their basements, but in this article we’re going to broaden that discussion considerably.


Basements, as we know them, are a relatively recent development in housing, and to a great extent unique to our climate. If you travel into the southern U.S. you’ll find most homes are still constructed on a concrete slab with some reinforcement near the outside edges to deal with the weight of the walls.

So, why do we have basements? 

It all has to do with the very cold winters and the depth to which the ground becomes frozen. Typically, we want to have the top of the footing for a wall about 4 feet below the ground level around a foundation. If we don’t, and the ground freezes to below the footing, you run the risk of having the foundation walls suffer from “frost heave” in the spring, resulting in degradation of the house structure over a few years.

You may ask “How does that contribute to having a basement?” 

Not every home in our area has a basement, but in general, with the development of sophisticated digging equipment home builders have learned that the cost of excavating the mound of dirt inside the foundation isn’t that much of an additional cost, and it provides space for most of the mechanical needs of the home, like the furnace, water heater, heat recovery ventilator, perhaps a water softener, and sometimes the electrical panel. It also makes the installation of ductwork for a forced air heating system, and plumbing for both drains and supply lines much easier. Of course, the creation of this space has also meant changes in the way we heat and cool our homes with high efficiency furnaces and forced air circulation systems.


We have been tormented with water seeping into basements ever since they came into being. 100 years ago, the basement space was often left with a dirt floor and was usually only inhabited by a few mice. About 80 years ago, we began to build the foundation with poured concrete (although for a time, concrete block foundations became popular). This provided a structurally sound wall on which to build a home, but also one that allowed the interior space to be hollowed out and become a useful part of the dwelling. But concrete is porous and when there were heavy rains, water would seep into the basement. Of course, to make the space more usable, we also began to cover the floor with concrete. Contrary to popular belief, the concrete floor of a basement is there to keep the dust down from the otherwise dirt floor, and it keeps the exterior walls from being pushed in towards the centre of the home over time. Since concrete is porous, any moisture underneath it will also seep up through the basement floor.

I think we’re all familiar with the damage that dampness in a basement can cause. When you venture into many older homes, you can detect the odour of mould, usually called “mustiness”. If you look carefully, you may find evidence of mould growing on the interior walls. Mould requires moisture in order to live and the amounts that seep in through the concrete provide an ideal habitat, particularly when combined with enough heat to keep from freezing.

The first attempts to control this infiltration of water were to use tar to coat the exterior of the foundation, and it worked pretty well, but not in every case. When water was allowed to accumulate against the wall, the tar would break down over time and we’d have a leak. To combat that we began to install a drain, called a perimeter drain that runs all the way around the outside of the foundation at the same level as the footing, just below the basement floor level. That was an improvement, until the drain became plugged with silt and was no longer functional. And even if they worked fine, some people would still get water seeping up through the floor, usually because there may be an old underground stream or a spring under some part of the house.

Today, builders have an army of tools to combat water that wants to get into the basement of your home. They still tar the exterior of the foundation wall and install a perimeter drain, but that drain is now covered with a fabric wrapping to keep the silt from getting in. In addition, the drain is now surrounded with “clear stone”, basically crushed rock with no silt or sand mixed in so there’s lots of passageways for the water to get to the drain. The outside of the wall, after being tarred, is covered with a heavy plastic dimpled sheet that allows water that does get close to the foundation to run down into the drain and the space outside the foundation is also filled with clear stone. Several inches of clear stone are usually placed on the dirt beneath the floor before the concrete floor is poured.

In all, I think we’re winning the war against water getting into our basements, but to a great extent how hard that battle is will depend on the age of the home.


One of the most important things that everyone can do to minimize the risk of water damage is to keep it away from the foundation as much as possible. The ground around a newly constructed home tends to settle over several years, and you’ll see many homes with the ground sloping towards the house. Eavestrough downspouts that are not directed at least 6 feet away from the foundation also add to the problem. Spring is a perfect time to check around the outside of your home to ensure the soil is sloping away from the house, but keep it at least 6 inches below any siding or brick; those vent holes between the bricks serve a very important function, so don’t cover them over. You may have a driveway or patio that runs right beside the foundation in places, and it may have sunk somewhat on the side next to the house. It’s the perfect time to get that kind of repair-work done. If you spot any minor cracks in the foundation, make note and monitor them each year to see if they are getting bigger, and if they are, get them repaired before you have a major problem.

If your landscaping permits, it’s best to not spray water within 2 feet of the foundation, and it’s best for the plants to not crowd them right against the structure either. Also, make sure the eavestroughs are cleaned regularly (at least twice a year) and be sure to seal all the penetrations that go through the basement wall for things like exhaust fans, dryer vents, and electrical outlets.

Basement windows can also be a source of water infiltration. A weak part of a foundation is at the corner of windows that have been installed along the cement wall, so you’ll often find cracks that start at those corners. Wherever you don’t have at least 4 inches between the ground level and the bottom of the window sill, it’s best to install a window well. Where builders have window wells, they are supposed to install a standpipe (a vertical tube) that is tied into the perimeter drain. If that’s not the case, it’s best to hire a contractor to dig down to the footing to install one.

Another solution is to have a dehumidifier running in a basement of your home, particularly in wetter weather. Alternatively, you’ll find that running your furnace fan constantly will not only keep the humidity from building up in the basement, but it will also keep the whole home at a much more uniform temperature. And with high efficiency variable speed fan motors being used in today’s furnaces, you will experience greater comfort at a lower cost and the constant air movement will ensure that moisture accumulation is minimized.


Perhaps you’ve read about radon gas, a naturally occurring radioactive material that is formed as uranium breaks down over time. Uranium is found in all rocks and soils to some degree, so it will be impossible to eliminate the production of radon. Many studies have shown that when radon escapes into the atmosphere it is so dilute that it has no effect on human health. The danger occurs when radon is trapped in our homes and begins to accumulate to dangerous levels. Of course, in the interest of energy efficiency, we are now building homes that are much tighter than they used to be, and even with the use of heat recovery ventilators the accumulation of radon in our homes can still be a concern.

Builders now are required to put a gas resistant plastic membrane on top of the gravel that’s under the basement floor before the concrete is poured, and to provide a venting system to allow any accumulation of radon that might seep up under the foundation to escape to the atmosphere. This is intended to keep the levels of radon in our homes below what is the accepted danger level of 200 becquerels per cubic meter. If there’s concern about the coldness of the concrete floor, they may also place some foamed insulation material under the concrete. Of course, this membrane will also help reduce the chance of water getting into the basement from beneath the floor.

If you have an older home and want to check on the levels of radon in your home, radon testing is relatively simple and inexpensive. Radon test devices can be purchased by phone or over the internet and are available at some home improvement retailers. You may also contact Health Canada at 613-946-6384 or on their website ( for more information about radon.

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