Mold and air quality testing in London

London gets about 3,809 heating degree-days a year and has a winter design temperature of −18.4°C, according to NRCan's HOT2000 climate data for London. On cold days, exterior corners, closets on outside walls and window frames get cold enough for condensation, which is where mold usually starts in London houses.

Of London's 119,295 houses (single-detached, semi-detached, row houses and duplexes), 25% were built before 1961 and 66% before 1991, according to the 2021 Census. Older basements without a moisture barrier and houses that were air-sealed without adding ventilation are common trouble spots.

• You smell mustiness but can't find the source.
• After a leak or flood, to check that cleanup worked.
• Before buying an older house with signs of past water damage.

If you can see mould, you usually don't need a test to know it's there; you need to fix the moisture and clean it up properly.

No Canadian province has a mandatory mould standard for homes. Health Canada's guideline sets no numerical limit: it says to fix moisture problems and clean up visible mould.

Ask any London tester which lab analyzes their samples, and look for one accredited under AIHA's EMLAP program for environmental microbiology. Pair sampling with a ventilation and humidity assessment, which finds the cause.

Ventilation and humidity assessments in London · Our mold and indoor air quality guide