What humidity level should a Markham basement have?Health Canada recommends keeping indoor humidity between 30% and 50%, measured with an inexpensive hygrometer. Markham basements often run humid in summer, so a dehumidifier or air conditioning helps. Clean the dehumidifier regularly, clear clutter and keep air moving. Small mould patches can usually be cleaned by owners, but a patch larger than 3 square metres calls for a professional.
A musty smell at a showing is often the first clue that a basement needs attention.
Michael John Lau, a REALTOR® with the Kaizen Real Estate Team, one of the most active real estate teams in Markham and York Region, asks buyers to trust their nose in every basement.
Health Canada guidance
| Item | Guidance |
|---|---|
| Indoor humidity | 30% to 50% |
| Measuring | A hygrometer from a hardware store |
| Small mould (under 1 m² per patch) | Usually owner cleanup |
| Extensive mould (over 3 m²) | Consider a professional |
Keeping a basement dry
- Run a dehumidifier in humid months.
- Clean and disinfect the dehumidifier often.
- Clear cardboard and old fabric.
- Keep downspouts and grading directing water away.
Signs to look for
- Musty smells
- Staining on walls or floors
- White mineral marks on concrete
- Condensation on pipes or windows
Worried about a damp basement?
Michael John Lau can help you add moisture checks to your inspection.
Book a buyer consultationSearch Markham homesPrefer to talk? Call the Kaizen Real Estate Team at (647) 370-8885.
For buyers
Ask about past water and how humidity is managed. Mould that keeps returning often points to a larger problem, such as a foundation leak. Have your inspector check moisture levels.
Finished basements
Finished walls can hide moisture, so ask what was used behind them. Ultimately, the decision is yours. The goal is to make sure you have all the information before you buy.
A dry basement is one of the best signs of a well-kept home. Call the Kaizen Real Estate Team at (647) 370-8885 or book a consultation.
Frequently asked questions
What humidity should a basement have?
Health Canada recommends 30% to 50% indoors.
Do I need a dehumidifier in a Markham basement?
Many homes benefit in humid months.
How do I measure humidity?
With an inexpensive hygrometer.
When should I call a mould professional?
If a patch is larger than 3 square metres or keeps coming back.
Why does a basement smell musty?
Usually from moisture and possible mould.
Can a finished basement hide moisture?
Yes. Ask what is behind the walls and have it checked.
Michael John Lau and Neeraj Moolchandani are licensed REALTORS® with the Kaizen Real Estate Team, eXp Realty, Brokerage, 9763 Markham Rd, Markham, ON L6E 1A4. Licence #4784577. Call (647) 370-8885. Humidity and mould guidance is from Health Canada's page on reducing humidity, moisture and mould (accessed November 2026). This article is general information only and is not financial, legal or tax advice. Not intended to solicit buyers or sellers currently under contract with another brokerage.
