You just invested in renovations, and instead of a fresh and comfortable home, a musty smell sets in. It's frustrating, and it's more common than you'd think, especially in older homes in Old Lévis.
In most cases, the explanation comes down to a broken balance between the home's airtightness and its ventilation. But be careful: a smell alone does not confirm the presence of mold. At Solutions Rénovation Québec (RBQ license 5811-7821-01), we often see this kind of situation after renovations. We don't do laboratory air analysis, but we know how to recognize the signs that warrant a serious evaluation of the work.
Why does the musty smell appear after renovations?
A renovation changes how a house behaves. By making the envelope tighter, we alter the way air and moisture circulate, sometimes without realizing it.
The result is a house that retains heat better… and sometimes moisture better. Here are the two main mechanisms at play.
A tighter house, but not ventilated enough
When you change the windows, add insulation or seal air leaks, you reduce infiltration. That's the goal: fewer drafts, lower heating bills.
The problem is that the moisture produced indoors used to escape through those same leaks. A tighter house that keeps its old ventilation system therefore ends up accumulating water vapor. The air becomes heavy, and the smell follows.
Here, we need to distinguish three things that are often confused. An exhaust fan (bathroom, range hood) removes air from a single room to the outside. An air exchanger, on the other hand, renews the air throughout the entire house. And the heat recovery ventilator, the famous HRV, does the same thing while recovering some of the heat from the outgoing air. All three do not play the same role.
Moisture sources that are always present
Even with good ventilation, moisture continues to be produced every day: showers, cooking, drying laundry indoors, a damp basement, an infiltration or capillary rise through the foundation. Improved ventilation helps manage the normal moisture of daily life, but it will never fix a leak or a drainage problem. If water is getting in somewhere, you first need to stop the water.
The particularities of older homes in Old Lévis
Old Lévis has a character you don't find everywhere: stone houses, brick houses, wooden frames that have weathered the decades. These buildings were designed to «breathe» in a certain way.
When you renovate them with modern materials without taking this logic into account, you can create problems that didn't exist before. The issue isn't the age of the house, but the compatibility of what you add to it.
When modern materials trap moisture
An old stone or brick wall manages moisture by letting it migrate and evaporate. If you double it with insulation and a waterproof vapor barrier without analysis, you can block this natural drying. Moisture then remains trapped in the wall, where you can't see it.
The right approach depends on the exact composition of the wall and its exposure to wind, rain and sun. A south-facing wall doesn't behave like a north-facing wall that takes the brunt of the weather. That's why we evaluate the assembly before proposing a solution, rather than applying a one-size-fits-all recipe.
The risk of a double vapor barrier
A classic trap: ending up with a membrane that prevents drying on both sides of the wall. When moisture can't dry toward the inside or the outside, it accumulates and eventually causes damage. We therefore never prescribe a specific membrane without having examined the existing assembly, because the wrong decision here costs dearly later.
How to identify the causes without making the problem worse?
Before calling anyone, you can already observe certain things in your home. These checks don't replace an evaluation, but they help guide the next steps.
The important thing is not to make the situation worse by opening walls or scraping suspicious materials. You observe, you take notes, you don't demolish.
The homeowner's preliminary checks
Get a hygrometer (a few dollars at the hardware store) and measure the relative humidity in the affected rooms. Note which rooms smell the most, at what time of day, and whether it gets worse after a shower or rain. Observe condensation on the windows and check that your fans and air exchanger start properly when you turn them on. That's it. You don't scrape anything, you don't open any walls.
When should you request a specialized evaluation?
Certain signs warrant having the situation evaluated: a smell that persists despite ventilation, stains, swollen or deformed materials, condensation that keeps coming back, or a clear worsening after rain. If members of the household experience symptoms (cough, irritation, headaches), consult a health professional first. And when mold is visible over a large area, you need a specialist in investigation and decontamination, not just a coat of paint.
Describe the work done and the signs observed to SRQ to discuss the next steps.
What humidity level should you aim for and what solutions should you consider?
Once the signs are identified, the question becomes: what are we aiming for, and where do we start? The answer almost always combines two aspects, moisture control and ventilation.
And above all, an order to follow: fix the cause before redoing the finishes.
Adjust ventilation and control moisture at the source
Health Canada generally recommends maintaining indoor relative humidity between 30 and 50%.. In the middle of a Quebec winter, the goal is rather the lower end of this range: if condensation is running down your windows, it’s a sign that the level needs to be lowered.
Concretely, this can mean installing or adjusting an HRV to renew the air in the house, making sure that the bathroom and kitchen exhaust fans actually vent to the outside, and occasionally dehumidifying a basement that is too humid. It must be said honestly, however: a dehumidifier alone will not solve a ventilation problem or an infiltration. It treats a symptom, not the cause.
Correct the cause before redoing the finishes
The logical order is this: we look for the source of the humidity, we check the ventilation and the assemblies, we correct the infiltration or the identified defect, and only then do we repair the damaged surfaces.
Skipping steps is the best way to pay twice. An antifungal paint applied to a wall that is still damp will mask the problem for a few months, then it will come back, often worse. You never close up a wall over a cause you haven't fixed.
Before repainting or closing up a wall, have the probable cause and the necessary work clarified.
How much can fixing a humidity problem cost?
It's hard to give a single figure, because everything depends on what we find. The price varies according to the source of the problem, the accessibility of the premises, the layout of the ventilation ducts, the extent of the finishing repairs and whether or not decontamination is necessary.
For informational purposes only, the installation of an HRV in Quebec is generally between $2,300 and $6,500 depending on the model and complexity (2026–2027 estimate, to be validated with recent local sources). This is not an SRQ quote, and any potential financial assistance (for example through a program like Rénoclimat) must be verified according to the criteria in effect at the time of the work. The only way to get a real figure is a quote based on your actual situation.
Why entrust the evaluation of the work to SRQ?
We don't present ourselves as a laboratory or as a certified mold expert, that's not our trade. Our trade is well-done residential renovation, and it starts with understanding what's happening at your place before proposing anything.
A clear process, from needs assessment to delivery
Our way of working is simple: we talk with you and assess the work on site, we prepare a detailed quote, we plan the job site, we execute, we verify and we deliver clean. Every step is transparent. If the situation goes beyond general renovation and requires an air quality or decontamination specialist, we tell you clearly rather than improvising.
A local business and concrete commitments
SRQ is a business from your area, with its RBQ license 5811-7821-01, more than 10 years of combined experience and more than 500 projects completed in the region. Our five-year warranty on labour applies according to its conditions, which we explain to you in advance, without surprise fine print. We prefer commitments we can keep to impossible promises.
Request a quote for the necessary renovation work, according to the identified cause.
FAQ: humidity after renovation in Lévis
What humidity level is recommended in winter in Quebec?
Health Canada suggests staying between 30 and 50% relative humidity. In winter, aim for the lower end of that range: if your windows are running with condensation, it means you need to lower the level.
Does a musty smell mean there is mold?
Not necessarily. The smell indicates excess humidity or a ventilation problem, but only an on-site check can confirm the presence of mold. A persistent smell is still worth taking seriously.
Should an air exchanger run continuously?
Not always, but it must run enough to renew the air, especially in winter when the house is closed up. Several models operate in cycles or adjust according to humidity. The important thing is that it actually does its job.
Can a poorly installed vapour barrier cause humidity?
Yes. A misplaced or doubled vapour barrier can prevent a wall from drying and trap humidity in it. It's a common problem in renovations of older houses, and it requires an assessment of the assembly.
Is an HRV mandatory in an already-built house?
No, an HRV is not automatically required in an existing house. Ventilation requirements mainly target new construction and certain major renovations. That said, in a house that has become very airtight, an HRV is often the most effective solution.
Do the stone walls of Old Lévis require particular materials?
Often, yes. Old walls manage humidity differently, and you must choose materials compatible with their ability to dry. The right solution depends on the composition of the wall and its exposure, hence the importance of an assessment.
Is a dehumidifier enough to solve the problem?
Rarely on its own. A dehumidifier reduces ambient humidity, but it doesn't renew the air and doesn't correct either an infiltration or a ventilation defect. It's a complement, not a complete solution.
Who to contact if the smell returns after the work?
Start by noting the signs observed and contact a contractor to have the work evaluated. In the case of extensive mold or health symptoms, a decontamination specialist or a health professional should be consulted.
A smell of humidity after renovations is not inevitable, and it's not normal either. It's a signal that must be listened to, understood and corrected in the right order, before redoing the finishes.
Contact SRQ to discuss your project and get a quote adapted to the required work.