Basements sure have come a long way. These days, we convert them into enjoyable, comfortable living spaces. Whatever purpose you give your basement, though—office, game room, home cinema—it’s vital that you make sure it offers a healthy environment for all occupants.

Features and factors to keep in mind

Basements have features that expose the people living in them to certain risk factors, like mould, carbon monoxide, volatile organic compounds, and radon.

Basement features Impacts

Limited natural ventilation and, often, no air exchanger

Humidity, stale air

Partly or completely underground

Vulnerable to infiltration by water or gases from underground

The lowest part of the building

Risk of flooding, sewer backup, etc.

The location where the various systems in the house are normally controlled (water, sewer, electrical, gas, security/alarm system, etc.)

Proximity of potentially hazardous devices and substances

Small window openings

Low level of natural lighting

Mould: it’s never innocuous

Mould is made up of microscopic fungi that grow in humid materials. It can be black, white or another colour, and can smell musty or earthy. To proliferate, mould needs moisture and a material it can live in: wood, paper, carpeting, etc. It develops in areas where:

  • water condenses on surfaces because of excessively humid air, a lack of ventilation or excessively low temperatures;
  • water infiltrates due to leaks from the roof or plumbing, a breach in the home’s exterior cladding, cracks in the foundations, or flooding.

These conditions occur frequently in basements.

Mould releases spores into the air, which everyone in the house can breathe in. This can lead to health problems such as:

  • irritation of the eyes, nose and throat;
  • coughing and phlegm buildup;
  • wheezing;
  • shortness of breath; and
  • asthma symptoms or allergic reactions.


Carbon monoxide: a silent enemy

Carbon monoxide (CO) is an invisible, odourless toxic gas that does not irritate the throat—so detecting its presence is impossible. It may be “silent,” but it can kill.

CO builds up rapidly in the blood, inhibiting its ability to carry oxygen throughout the body. The longer one is exposed to it, the worse the damage:

  • Mild exposure: flu-like symptoms, like headaches, runny nose, eye irritation, etc.
  • Medium exposure: drowsiness, dizziness, vomiting, disorientation, confusion.
  • Severe exposure: loss of consciousness, brain damage, death.

Carbon monoxide is released in cases of incomplete combustion of organic matter or when an appliance (e.g., a heater or generator) or vehicle burns fuel such as gasoline, propane or natural gas, wood, heating oil, etc. For this reason, if your home is equipped with a fuel-burning appliance, or has an attached garage where vehicles are started, you must install a certified carbon monoxide detector. Note that smoke detectors do NOT detect carbon monoxide, even in high concentrations.


Volatile organic compounds (VOC): pollution at home

Volatile organic compounds (VOCs) are chemicals that can be released into the indoor air of homes. They affect air quality and, in turn, the health of residents who breathe that air, especially if a room is poorly ventilated, which is often the case in the basement.

Cigarette smoke, paints, varnishes, glue, floor coverings, cleaners, air purifiers, furniture, combustion gases emitted by heating appliances and vehicles in the garage—the sources of VOCs are legion. Their most frequently observed consequences on health are various types of irritation, allergies, and central nervous system disorders.

According to a document published by Canada Mortgage and Housing Corporation (CMHC), chemical pollutants in the home can lead to:

  • acute reactions generally caused by accidental short- or medium- term exposure; and
  • chronic reactions related to prolonged exposure to low concentrations of substances.

Because of our harsh climate, our homes are built more air- and watertight—which means they trap more moisture and contaminants potentially toxic to our health. This is why a controlled mechanical ventilation system—i.e., an air exchanger, which is designed to completely replace the air in a home every three hours—is required in new homes. Another good idea is to seek out green products that contain no chemical compounds.


NB : bien que le site ait sont pendant anglo,, il n’y a pas d’équivalent précis de la page «Je me méfie des COV».

Radon: a radioactive gas

Hard as it may seem to believe, your home can contain radioactive gases, like radon, which is produced by the natural decay of uranium in the Earth’s crust. It is colourless and odourless, and can build up to high concentrations in a closed space like a basement.

A house can act like a vacuum, sucking up underground gases. Radon can seep in through any opening that is in contact with the surrounding soil: cracks in foundation walls and floor slabs, construction joints, gaps around utility lines and supporting studs, floor drains and sump pumps, water inlets, etc. At that point, it constitutes a serious health hazard, especially if exposure is prolonged; the effects are worsened if the people exposed are smokers.

Smokers who are exposed to high concentrations of radon are at significantly greater risk of developing lung cancer:

  • An average of 16% of lung cancer cases in Canada are attributable to radon exposure.
  • Radon is the second leading cause of lung cancer after exposure to tobacco.

The only way to know whether you have a radon problem is to measure the concentration of the gas in your home. It’s a simple and very inexpensive process.

To find out more:

  • Read our comprehensive report on the topic: Radon in the house?
  • Talk to a CAA-Quebec residential advisor by calling 514 861-6162 or 1 888 627-6666.

NB : l’hyperlien pointait vers la FAQ sur le radon, qui n’est qu’une partie du dossier spécial sur la radon sur votre site. Nous avons modifié le lien en anglais pour qu’il mène au niveau précédent.

If you plan on renovating your basement for liveability, keep in mind that various other factors can have an impact on your well-being and that of the other members of the household. These include accessibility of safety exits, properly functioning smoke detectors, the intensity of electromagnetic fields (which is largely dependent on the concentration of electronic devices and the quality of your electrical system), and sound insulation. By carefully considering all of these aspects, you should be able to get the most out of these extra living spaces.