Mould and indoor air quality (IAQ) testing in Durham Region: Port Perry, Uxbridge, Brock

How Durham Region is built

Before 1961 24%
1961–1990 42%
1991–2000 13%
2001 or later 21%

Each house stands for one in ten of Durham Region's 19,285 houses (single-detached, semi-detached, row, duplex and mobile homes), drawn by when it was built. The glow shows the usual pattern: older houses tend to be leakier and less insulated. More snow in the drawing means more heating degree-days: a longer, colder heating season. Sources: Statistics Canada 2021 Census (table 98-10-0233-01), Environment and Climate Change Canada 1981–2010 climate normals (Lindsay Frost) and the National Building Code 2020 January design temperature for Port Perry.

This page covers north Durham: the townships of Scugog (Port Perry), Uxbridge and Brock. Oshawa, Whitby, Ajax, Pickering and Clarington have their own pages, which also cover their hamlets.

Why mould shows up in Durham Region homes

Environment and Climate Change Canada's 1981–2010 climate normal at Lindsay Frost (30.6 km from the middle of the area) is 4,357 heating degree-days a year, with a January mean of −8.4°C. On cold days, exterior corners, closets on outside walls and window frames get cold enough for condensation, which is where mould often starts.

Of the 19,285 houses in Durham Region (single-detached, semi-detached, row houses, duplexes and mobile homes), 24% were built before 1961 and 66% before 1991, according to the 2021 Census. Older basements without a moisture barrier, and houses air-sealed without adding ventilation, are common trouble spots.

Mould inspection: when sampling helps

Start by looking and smelling: stains, discoloured patches, peeling paint and a musty odour, especially in basements, bathrooms, window frames and closets on outside walls. Health Canada says measuring mould concentrations or identifying species is usually unnecessary: if you can see or smell it, fix the moisture and clean up.

Air or surface sampling helps when you smell mustiness but can't find the source, after a leak or flood to check the cleanup worked, or before buying a house with signs of past water damage. Ask which lab analyzes the samples and look for one accredited under AIHA's EMLAP program.

Cleanup and remediation: the size rules

CMHC and Health Canada sort mould by size, and the size decides who should clean it up:

Size	What counts	Who should clean it
Small	One to three patches, each smaller than 1 m²	A healthy homeowner, with water and unscented dish detergent (CMHC)
Medium	More than three patches, or patches between 1 and 3 m² (32 square feet)	Trained help; homeowners only with training and precautions
Large	A patch larger than 3 m², or many patches through the house	A qualified mould remediation contractor (CMHC)

Fix the moisture source first: a leak, poor drainage, or condensation from high humidity. Health Canada recommends 30–50% relative humidity.
For a small cleanup, wear safety glasses or goggles, an N95 mask if possible and household rubber gloves. People at risk from mould shouldn't clean it and should stay away.
Health Canada suggests professional help for extensive mould, especially growth that keeps coming back after cleaning.

Choosing a tester or contractor

Ask any tester which lab analyzes their samples and what the report will recommend; a good report points to the moisture source. For remediation, get two or three written quotes that describe containment, what will be removed and how the area is cleaned. No province has a mandatory mould standard for homes, and Health Canada sets no numerical limit.

Great Lakes–St. Lawrence Southern Ontario and southern Quebec

What this means in Durham Region’s climate

Cold winters and hot, humid summers: seal the attic, dry the basement, plan cooling.

This region has real winters and hot, humid summers, so bills come from both heating and cooling. Natural gas heats most Ontario homes, while most Quebec homes use low-cost electricity. An EnerGuide evaluation here should cover air sealing and the attic, cooling and dehumidification, and keeping the basement dry before insulating it.

Keep the basement dry before insulating. Basements can be about 20% of heat loss, but insulating a damp basement from the inside can rot the new wall. Flash floods have hit Toronto and Montreal repeatedly. Ask: Ask the advisor to check grading, downspouts, foundation cracks and the sump, and to look for damp spots or white mineral stains.

What else homes in Oshawa need →

Sources for this climate guide · checked October 26, 2026

Communities we cover in Durham Region

Every town, village and hamlet below is part of this page, grouped by municipality (2021 Census population).

Township of Scugog 21,581Caesarea, Greenbank, Nestleton Station, Port Perry, Prince Albert
Township of Uxbridge 21,556Goodwood, Leaskdale, Udora
Township of Brock 12,567Beaverton, Cannington, Sunderland

Covered on city pages: Pickering (Brougham, Claremont, Greenwood, Whitevale); Clarington (Hampton, Newcastle Village, Newtonville, Orono); Whitby (Ashburn); Oshawa; Ajax.

Mould and indoor air quality testing in Durham Region: common questions

Do I need mould testing in Durham Region if I can see mould?

Usually not. Visible mould needs cleanup and a fix for the moisture source. Sampling helps most when you suspect mould you can’t see.

How much mould can I clean myself?

CMHC says a healthy homeowner can clean one to three patches, each under 1 m², with water and unscented dish detergent. Larger areas need trained help or a remediation contractor.

When should I hire a mould remediation contractor?

For a single patch over 3 m², many patches through the house, or mould that keeps coming back after cleaning (CMHC, Health Canada).

Is there a legal mould limit for homes in Canada?

No. Health Canada sets no numerical limit; its guidance is to control moisture and clean up mould.

Mould and indoor air quality testing in Durham Region