Montreal is home to thousands of century-old houses. Stone, brick, solid wood—these buildings tell our story.
But behind their charm lies an invisible problem that affects the health of the families living there: indoor air can be up to five times more polluted than outdoor air. Trapped moisture, hidden mold, and historical contaminants—these risks are common in neighborhoods such as the Plateau-Mont-Royal, Rosemont, and Old Montreal.
This article explains why indoor air quality is often a problem in older homes. You’ll learn about the real risks, the myths to disregard, and, most importantly, heritage-friendly solutions that protect your health without altering the character of your home.
Why Air Quality Is Often a Problem in Centennial Homes
Houses built 100 years ago didn't have the same needs as they do today. Back then, there were no mechanical ventilation systems. There were no energy-efficient windows.
Buildings used to «breathe» naturally through cracks, porous joints, and active chimneys. But today, after decades of renovations and modern additions, this "breathing" no longer works as it used to.
A ventilation system designed for another century
Homes built over a century ago relied on natural air infiltration to remove moisture and refresh the air. But when you install airtight doors, energy-efficient windows, and insulate the walls, you trap moisture inside.
The result? Stale air remains trapped inside. CO₂ builds up.
According to Health Canada, CO₂ levels in some poorly ventilated homes can reach 1,483 ppm—well above the recommended threshold of 1,000 ppm. This is what causes the chronic fatigue, headaches, and difficulty concentrating that many residents experience without understanding why.
In older homes without mechanical ventilation, the air simply doesn't circulate quickly enough.
Montreal's climate exacerbates the problems
Montreal experiences two extremes: long, cold winters and hot, humid summers. These conditions put a heavy strain on older structures.
In winter, when it’s -20°C outside and 21°C inside, condensation forms on cold walls and in uninsulated areas. Water seeps into porous materials such as brick and old plaster.
In the summer, relative humidity often rises above 60 %. Without ventilation to remove this moisture, mold thrives in dark corners, behind furniture, and inside walls.
The Quebec National Institute of Public Health (INSPQ) confirms that excessive humidity promotes fungal growth and increases respiratory risks, especially among children and the elderly.
The Main Indoor Air Contaminants in Centennial Homes
Living in an older home often means living with invisible pollutants. Some date back to when the house was built. Others build up due to poor ventilation.
Here are the most common ones in Montreal.
Mold and Trapped Moisture
Mold loves old houses. Why? Because it finds exactly what it needs: moisture, organic materials, and poor air circulation.
According to data from Health Canada, poorly ventilated homes have a more than 40 % increased risk of mold. In neighborhoods like the Plateau and Rosemont, where many duplexes and triplexes date from before 1920, this is a common problem.
What are the symptoms? A persistent cough, eye irritation, nasal congestion, and sometimes asthma attacks. Children and people with allergies are particularly vulnerable.
Mold is often found behind old wallpaper, under floors, or in unheated outdoor closets. Even if you can't see it, it can affect your health every day.
Asbestos, Lead, and Historical Dust
Before 1980, asbestos was everywhere: around pipes, in ceilings, and under floor coverings. Lead was found in paint, solder, and sometimes even in plumbing.
These materials pose no danger as long as they remain intact. But as soon as you start renovating—whether you’re drilling into a wall, tearing up an old floor, or sanding a painted surface—particles are released into the air.
Exposure to lead affects children’s cognitive development. Asbestos, even in small amounts, increases the risk of serious respiratory diseases in the long term.
If your home was built before 1980, have the materials tested before starting any renovations. Local companies offer non-destructive testing that gives you an accurate assessment without damaging your walls.
Modern Pollutants in Old Buildings
Century-old houses are not isolated from the outside world. They let in more air than newer buildings—but not always clean air.
Montreal now experiences episodes of wildfire smoke almost every summer. In June 2023, the air quality index (AQI) reached dangerous levels for several days.
Older homes, with their poorly fitting windows and porous foundations, allow 20 to 30 % more fine particulate matter (PM2.5) to seep in than modern, well-sealed homes.
Add to that the volatile organic compounds (VOCs) from cleaning products, furniture, and recent renovations, and you end up with a cocktail of pollutants that lingers in a poorly ventilated space.
Common Myths About the Natural «Breathing» of Old Houses
Many homeowners believe that their older homes ventilate on their own. This is a dangerous myth that prevents them from taking action.
“Century-old houses breathe on their own”
Yes, old houses let air through. But that doesn't mean they're properly ventilated.
Uncontrolled air infiltration is exactly that: uncontrolled. Air enters through cracks in the cold, damp basement. It exits through the attic, which gets overheated in the summer. But in between, it doesn’t mix enough to refresh the air in the main rooms.
This false sense of security causes people to overlook signs of excessive moisture, mold, or high CO₂ levels. Meanwhile, air quality slowly deteriorates.
The reality? Partial airtightness combined with a lack of mechanical ventilation traps moisture and contaminants right where you live.
“Opening the windows is enough to improve air quality”
In the summer, maybe. But in the winter, opening the windows quickly becomes impractical. You lose heat, your heating costs skyrocket, and the cold outside air only dries out the indoor air without solving the problem of moisture in the walls.
Opening the windows doesn't provide any filtration either. You let in pollen, diesel particles, and smoke from wildfires along with the fresh air.
Health Canada recommends controlled, filtered ventilation—not just opening a window whenever you think of it. This is especially true in a century-old home, where air exchange requirements are higher due to older building materials and structural moisture.
How to Assess Indoor Air Quality in a 100-Year-Old House in Montreal
Do you live in an older home and wonder if the air you breathe is healthy? Here's how to find out.
Visible and Invisible Clues
Some signs are obvious. Others are more subtle.
Start by taking a look: Do your windows often get fogged up in the winter? This is a clear sign that the relative humidity is too high and that the air isn't being refreshed enough.
Is there a smell Do you notice a musty smell in certain rooms, especially in the basement or in closets? Even if it's faint, this smell often indicates the presence of hidden mold.
When it comes to your health, be on the lookout for recurring symptoms: chronic fatigue first thing in the morning, headaches that go away when you go outside, a persistent cough for no apparent reason, or allergies that get worse indoors.
These indicators don't lie. They point to an indoor air quality (IAQ) problem.
Recommended Tests for Older Homes
To confirm your suspicions, consult a specialist who can measure air quality using precise instruments.
A basic test costs between 300 $ and 600 $ in Montreal. It measures CO₂, relative humidity, fine particulate matter (PM2.5), and sometimes volatile organic compounds (VOCs).
If your home was built before 1980, have it tested for asbestos and lead before starting any renovations. You can also test for radon—a naturally occurring radioactive gas that accumulates in basements and is the second leading cause of lung cancer in Canada.
Radon test kits are sold at pharmacies and hardware stores for about 50 $. You set them up for 3 months, then send them to the lab for analysis.
Would you like to have the air quality in your home tested without any invasive work? Vortex Air offers free, no-obligation inspections. We take measurements, explain the findings, and help you understand what’s really going on in your property.
Tailored solutions to improve indoor air quality without altering the character of a century-old home
Improving indoor air quality in an older home is possible. But it requires solutions that respect historic buildings and work within the constraints of Montreal’s climate.
Gentle Mechanical Ventilation (VRC/HRV)
A heat recovery ventilator (HRV) is the most efficient solution for century-old homes. It brings in fresh, filtered air from outside while recovering 60 to 85 % of heat from the stale air that is expelled.
The result? You improve indoor air quality by 50 % or more, without wasting energy.
In an older home, the HRV is installed strategically to minimize its visual impact. Sometimes, the existing ducts from an old heating system are used. Other times, the ducts are routed through hidden spaces—closets, basements, and attics.
The initial investment ranges from 2,500 $ to 5,000 $, depending on the complexity of the installation. But you’ll save between 10 % and 20 % on your heating costs each year, in addition to breathing much healthier air.
Maintenance of Existing Ducts and Systems
Many century-old homes have ventilation ducts that have never been cleaned. Ever.
Inside, you’ll find decades of dust, pet hair, mold spores, and sometimes even construction debris left behind from past renovations.
Professional cleaning removes these accumulated contaminants and immediately improves the quality of the air you breathe. It also improves the energy efficiency of your heating and air conditioning system.
At Vortex Air, we follow the protocols of the INVC (National Institute of Ventilation and Air Conditioning). We use rotating brushes and HEPA vacuums, and we inspect the entire system with a camera to ensure that no contaminants are left behind.
Are you wondering if your ducts need to be cleaned? We offer a free inspection to assess the condition of your system and give you the straight facts. No pressure—just honest advice.
Moisture and Water Infiltration Control
In a century-old house, controlling humidity means protecting both the structure and the health of its occupants.
Start by identifying the sources of water infiltration: a leaky roof, clogged gutters, or cracks in the foundation. Fix these problems before investing in ventilation; otherwise, you’ll just be ventilating moisture.
Next, use a dehumidifier in the basement during the humid months. Keep the relative humidity between 30 % and 50 % in the winter, and between 40 % and 60 % in the summer.
For water leaks cold air, seal problem areas in a targeted manner—around windows, doors, and utility openings—without completely blocking the natural drying ability of old walls.
It’s a delicate balance. If it’s too airtight, you trap moisture. If it’s not airtight enough, you waste energy. A specialist in older buildings can help you find the right balance.
Regulations and Recommendations in Quebec for Older Homes
In Quebec, there are clear recommendations regarding indoor air quality, although legal requirements for private residences remain limited.
Health Canada proposes a limit of 1,000 ppm of CO₂ for residential spaces. This is a threshold that many older homes exceed without their owners even knowing it.
The Régie du bâtiment du Québec (RBQ) regulates renovation work, especially when it involves hazardous materials such as asbestos. If you are renovating a home built before 1980, you must comply with safety standards to prevent asbestos fibers from being released into the air.
For landlords, there is currently no legal obligation to test or improve indoor air quality. However, tenants have the right to live in a healthy home. If a problem with mold or excessive moisture affects their health, the landlord may be required to take action.
As for maintenance, do the following: clean your ducts Ventilation or installing a heat recovery ventilation system is a matter of preventive maintenance—not a legal requirement. But it’s a smart investment that protects your property and your family’s health.
Why Montreal's Centennial Homes Require Local Expertise
Improving indoor air quality in an older home is not the same as doing so in a new construction. The challenges are different. So are the solutions.
A reality different from that of modern homes
Traditional materials—solid brick, plaster on lath, solid wood—behave differently than modern gypsum and OSB. They absorb and release moisture slowly. They expand and contract with the seasons.
Montreal's urban density adds another layer of complexity. Many century-old homes are attached duplexes or triplexes. They share walls, chimney flues, and sometimes even ventilation systems.
The result? A problem at a neighbor’s house can affect your indoor air quality. A poorly planned renovation in one home can cause condensation in another.
Not to mention urban pollution: car exhaust on Avenue du Parc, industrial fumes near the port, and fine particulate matter that accumulates in densely built-up neighborhoods.
All of this calls for a tailored approach. There is no one-size-fits-all solution.
Vortex Air's Ventilation Approach for Older Buildings
At Vortex Air, we've been working with century-old homes for over 10 years. We understand their unique characteristics. We respect their history.
Our method always begins with a thorough inspection and at no cost. We assess the condition of existing ducts, measure air quality, and identify sources of moisture and contamination.
Next, we offer tailored solutions—never invasive. We use non-destructive techniques to clean the ducts, install discreet HRVs, and improve ventilation without compromising the architectural character of your property.
We follow the INVC protocols, and we are in the process of obtaining NADCA certification—the North American standard for duct cleaning. Our technicians are trained to work with care to preserve older materials and adhere to the strictest safety standards.
Above all, we’re honest with you. If your ducts don’t need cleaning, we’ll tell you. If a simple repair is all that’s needed, we won’t try to sell you a whole new system.
Do you have questions about the air quality in your century-old home? Call us at 514-214-7492 or visit vortexair.ca to talk to a specialist in historic homes in Montreal. We'll explain what's really going on, with no pressure and at no cost.
FAQ – Indoor Air Quality in Centennial Homes in Montreal
How often should you test the air quality in an older home?
Have a comprehensive test done every 2 to 3 years, especially if you notice recurring respiratory symptoms or if you've recently done any renovations. For radon, a test every 5 years is sufficient, unless you make structural changes to your basement.
Do stone houses have more moisture problems?
Not necessarily. Stone is porous and allows for some natural drying. But if it’s covered with a modern waterproof coating on the inside, moisture can become trapped between the two surfaces. That’s where mold grows.
Is it possible to install a VRC without major construction work?
Yes. In most homes that are over 100 years old, a mechanical ventilation system can be installed using existing spaces—such as the attic, basement, or closets. Installation usually takes 1 to 2 days and does not require major demolition.
Do wildfires really affect indoor air quality?
Absolutely. Fine particulate matter (PM2.5) easily penetrates poorly fitting windows and cracks in older homes. During periods of heavy smoke, it is recommended to keep windows closed and use an air purifier with a HEPA filter.
How can you tell if asbestos is present without demolishing the structure?
Hire a certified inspector who will take small samples from suspicious areas (insulated pipes, floor coverings, textured ceilings). Laboratory analysis costs between 50 $ and 100 $ per sample and provides a clear answer.
Is it up to the landlord or the tenant to take action?
In Quebec, landlords are required to provide safe and sanitary housing. If a problem with mold or excessive moisture affects the tenant’s health, it is the landlord’s responsibility to take action. The tenant must report the problem in writing and give the landlord a reasonable amount of time to make repairs.
Is there financial assistance available in Quebec?
Yes. The Rénoclimat program offers grants to improve energy efficiency, including the installation of HRVs. Some municipalities also offer tax credits for the renovation of historic properties. Check with your borough for more information.
Living in a century-old home in Montreal is a privilege. But it’s also a responsibility. These buildings deserve to be preserved—and the families who live in them deserve to breathe clean air.
Indoor air quality is not a luxury. It is a necessity, especially in older buildings that accumulate contaminants and trap moisture.
If you have any concerns about the air you're breathing, don't ignore them. A simple test, a free inspection, or even a conversation with a specialist can make all the difference.
At Vortex Air, we're here to help you. We've been working in Montreal for over 10 years, and we know century-old homes like the back of our hand.
Call us at 514-214-7492, visit vortexair.ca, or email us at info@vortexair.ca. We offer a free inspection, honest advice, and solutions that are as gentle on your home as they are on your health.
Because a century-old home that breathes well is a home that lasts for generations.
