Humidity affects your home through condensation. High indoor humidity can cause condensation when warm, moisture-laden indoor air contacts cold windows. Beads of water will start to form and roll down, soaking into your window frame.
If too much water soaks into your window frame, it can even seep into the walls and create mould or wood rot. Home insurance usually covers water damage, but prevention is better than cure. It’s more affordable to prevent condensation in the first place than fix the damage after it happens.
We reviewed Health Canada’s moisture and mould guide, Health Canada’s home-ventilation guide, Natural Resources Canada’s winter-humidity table, and Health Canada’s cool-mist humidifier guidance.
What Should The Humidity Be In A House In Winter?
During cold weather, aim for about 30% relative humidity, then adjust downward if condensation or frost appears. In warmer weather, you can raise the relative humidity to the 30% to 40% range, as long as windows and walls remain dry.
Keep humidity levels below 50%. Reduce humidity levels if condensation or frost occurs repeatedly.
Generally, lower the target relative humidity as outdoor temperatures drop or windows become less energy-efficient.
Adjust Indoor Humidity For Outdoor Temperature And Your Windows
Natural Resources Canada offers this table as a general guide for the maximum indoor relative humidity before window condensation is likely. Actual limits vary with window performance and air leakage.
| Outdoor temperature | Approximate maximum indoor RH |
|---|---|
| 0°C | 58% |
| -10°C | 44% |
| -20°C | 34% |
| -30°C | 25% |
| -40°C | 18% |
The better the insulation or the more glazing panes a window has, the higher the indoor humidity you can have before condensation occurs. If you have older, less energy-efficient windows, target the lower end of the range.
How Does Humidity Affect Your Home?
When indoor air comes into contact with a cold surface, the air near the surface cools. If it cools below its dew point, water vapour condenses into liquid water or frost.
That is why the same humidity reading may be fine one week and cause wet windows during a colder snap. Weather, window performance, airflow, and indoor moisture sources all matter.
How High Indoor Humidity Affects Your Home
Repeated condensation on windows, walls, ceilings, or cold corners can lead to mould growth and damage building materials.
Moisture can also affect wood, paint, finishes, insulation, and items stored against exterior walls.
How Low Indoor Humidity Affects Your Home
- Very dry indoor air can feel uncomfortable and may cause dry skin, irritated eyes, and throat irritation.
- Dry air can make wood furniture, flooring, or trim shrink or crack.
- Dry air can increase static electricity.
How To Measure Indoor Humidity
Use a hygrometer to measure relative humidity. Place it away from kitchens, bathrooms, direct sunlight, heating vents, and humidifiers so it reflects the general indoor air.
Record indoor humidity each morning along with indoor and outdoor temperatures and the condition of your coldest windows. These repeated readings are more useful than a single measurement taken after a shower.
Read More: Use the Canadian Home-Maintenance Checklist
How To Lower Indoor Humidity
- Reduce indoor moisture first. Use kitchen and bathroom exhaust fans, vent clothes dryers outdoors, and avoid drying laundry indoors during cold weather.
- Run a dehumidifier if readings stay high, especially in basements or rooms with persistent moisture.
- Improve ventilation. Make sure exhaust fans vent outdoors and are used long enough to remove moisture after cooking or bathing.
- Check for moisture sources such as plumbing leaks, roof leaks, wet basements, wet building materials, or unvented combustion appliances.
- Improve insulation or window performance if condensation happens often even at moderate humidity levels.
Read More: See How Home Insurance Treats Mould Damage
How To Raise Indoor Humidity Safely
- Check for water leaks or other moisture problems first. Do not add humidity to a home with active leaks, visible mould, or ongoing condensation.
- Turn up the humidifier in small increments and wait a day before increasing it again.
- Use only the type of humidifier recommended for your space. Keep it clean and follow the manufacturer instructions.
Does Insurance Cover Damage From Indoor Humidity?
Don’t assume that you are covered for condensation, mould, rot, or gradual humidity damage.
Coverage depends on the cause of loss, your policy’s terms and exclusions, any maintenance requirements, and evidence of what happened.
Water damage caused by a sudden, accidental event may be treated differently from damage that develops over time because of poor maintenance or repeated condensation.
If you notice persistent moisture, document what you find and take reasonable steps to prevent further damage. Keep records of repairs, inspections, and communications with contractors or insurers.