Mold Prevention & Remediation

What this page covers, and what you need before you start

This page is about diagnosing moisture and planning a response you can document. Before you call a remediation company, gather the observations that will determine both the cause and the scope of the work.

• Where growth is visible, with dated photographs and an approximate affected area.
• Indoor relative humidity readings, taken in the affected room and in the coldest room, across several days.
• Any known water event: leak, flood, ice damming, plumbing failure, or appliance overflow, with dates.
• Ventilation present in bathrooms, kitchen, and laundry, and whether the fans exhaust outdoors.
• Exterior conditions at the same wall: grading, downspout discharge, window sill, and cladding condition.
• Occupant health concerns, which may change urgency and who should be in the space during work.
• For rentals or condos, the notice obligations and who is responsible for the building assembly.

Decision workflow

1. 1

   Measure humidity before you clean anything

   A simple hygrometer log across rooms and days separates a whole-house humidity problem from a localised leak. Winter condensation on windows and exterior-wall corners points to humidity plus cold surfaces.

2. 2

   Trace the water

   Work outward and upward from the growth: plumbing above, roof and flashing, window and door perimeters, grading and downspouts, and unvented bathroom or dryer exhaust.

3. 3

   Scale the response to the area affected

   Health Canada distinguishes small, medium, and large areas, with different protective equipment and containment expectations. Read the guide before deciding to do it yourself.

4. 4

   Fix the source, then dry the assembly

   Repair the leak or the ventilation deficiency first. Materials must be verifiably dry before they are closed up, otherwise the growth returns behind the new finish.

5. 5

   Document everything for insurance and disclosure

   Photos, dates, invoices, moisture readings, and the repair scope. Sudden events and long-term seepage are treated very differently by insurers.

6. 6

   Set up prevention that you can maintain

   Bathroom and kitchen exhaust that actually vents outdoors, winter humidity control, downspout extensions, and a seasonal check on the same locations.

Questions to ask, and records to keep

Use these with a remediation contractor, and with your landlord or condo corporation where the assembly is not yours.

• What is the identified moisture source, and what evidence supports that conclusion?
• Is the source repair included in this scope, or only the cleanup?
• What containment, negative air, and protective equipment will be used?
• How will you verify materials are dry before rebuilding, and will you give me the readings?
• What materials will be removed, and how will reinstatement be handled and priced?
• What certifications, licensing, and insurance do your technicians hold in this province?
• For a rental or condo, who is responsible for the wall assembly, and what notice is required?
• What documentation will I receive that I can give to my insurer or a future buyer?

Primary sources for the rules that vary by jurisdiction

Federal guidance defines the recommended approach; the building conditions and contractor rules around it are local.

• Health Canada — guide to addressing moisture and mould indoors

  Establishes: Federal guidance on finding the moisture source, cleanup scale, and protective equipment; it is guidance, not a diagnosis of your building.

  Canada (federal) · Source link checked 2026-09-01

• Health Canada — mould and indoor air contaminants

  Establishes: The federal position on humidity control, mould health risks, and why testing spore counts is rarely the useful first step.

  Canada (federal) · Source link checked 2026-09-01

• Canada Mortgage and Housing Corporation (CMHC)

  Establishes: Federal housing research and homeowner guidance, including maintenance and moisture-management material.

  Canada (federal) · Source link checked 2026-09-01

• Your municipality's building department (permits, inspections, and closed-permit records)

  Establishes: Whether the work you are planning needs a permit, which inspections apply, and whether past work on the property was permitted and closed.

  Municipal · Source link checked 2026-09-01

Every source cited across the site, with what it does and does not establish, is listed in the home cost source ledger.

Where to go next

• Water damage guide

  Sequence for finding the source, drying, and documenting a water event.

• Basement waterproofing

  Interior versus exterior approaches and the evidence each one needs.

• Indoor air quality

  Ventilation, humidity, and contaminant sources in Canadian homes.

• Home insurance considerations

  How building changes and equipment can affect coverage, endorsements, and deductibles.

• Seasonal maintenance checklists

  Recurring inspection tasks you can print and record results against.

• Home cost source ledger

  Every primary source used on this site, the date its link was checked, and what it does not establish.