Precise Radon Test 

Radon levels can be measured using several different technologies. Although there are pros and cons to specific kinds of test types, the most important thing to do is to test a building for a long period of time (~3 months or more).

1. The amount of radon entering a building can fluctuate up and down quite a lot over the short term. From day to day, or even from hour to hour, radon can be very high and drop down to a much lower level. This is normal and is influenced by many factors, such as how your home ‘breathes’ outside air, furnace use, the weather and even geologic phenomena.
2. As a result of these normal fluctuations, measuring radon over a short period (hours or days) will often give a false reading compared to what is the average for a long period (several months). This false reading can be a false positive or a false negative, meaning you think you have a problem when you don’t, or (worse) you think you’re ok when you are not.
3. A precise radon test (that gives you a reading = actual amount of radon you are being exposed to over the long term) requires a measurement taken over several months, 3 or more.

What the science says: 

A study of 776 Canadian ‘closed house’ short (5 day) and long (90+ day) radon tests showed that long term testing was precise >96% of the time. In contrast, short term testing was “wrong” (meaning the short term test failed to predict the long term test outcome) 20-98% of the time depending on season.

Reference: Stanley et al. Radon exposure is rising steadily within the modern North American residential environment, and is increasingly uniform

Winter vs. Summer 

Radon was once thought to always be higher in a building during winter. This is no longer true. Data shows that radon is increasingly even across seasons, and in ¼ of homes can even be at its highest during summer periods.

1. For most of the 20th century radon levels in residential buildings was found to have been highest during the winter heating months (October to April in most Northern Hemisphere countries).
2. The reason for higher winter radon was thought to be due to two factors: (i) reduced dilution of inside air with fresh air when properties are closed up for winter, and/or (ii) forced air ventilation heating, wherein basement or ground level air is heated and distributed throughout a property more so than when the heating is off.
3. However, in the 21st century radon levels in North American are observed to be increasingly even across seasons, with many homes even showing higher radon in summer. The reasons for this are still emerging, but one hypothesis is increased use of air conditioning in summer and, as a result, the decreased ventilation of properties in the warmer summer months.

What the science says:

A study of paired winter and summer radon tests (using multiple different radon test technologies) in Canadian homes showed that 47.5% of buildings showed a minimal (<50 Bq/m3) difference, with 24.7% displaying ≥50 Bq/m3 greater radon in winter, and 27.8% displaying ≥50 Bq/m3 greater radon in summer.

Reference: Stanley et al. Radon exposure is rising steadily within the modern North American residential environment, and is increasingly uniform across seasons. In Press, 2019.

Radon & Real Estate 

A home mitigated for radon has the healthiest possible air and so is very desirable. As it is so ‘fixable’, high radon does NOT devalue real estate. A real estate transaction, however, is not a good time to do a radon test, as there is not enough time.

1. Homes with active sub-slab depressurization systems typically have radon levels well below the average for even an otherwise “low radon” household, often showing radon in the 0-10 Bq/m3 range. As the devices remove all soil gas entry into a home, they have the healthiest indoor air.
2. Many people consider homes with such devices “better”, and mitigation devices to be selling features.
3. Across North America, real estate professionals have been dealing with radon as part of the conversation between buyers and sellers in a real estate transaction. Radon is NOT a reason they report a home transaction to fall through – as it is so easily fixed.

4. A real estate transaction takes place over a short period – a few days or weeks at best. A real estate home inspection is not sufficient time  to perform a precise radon test. Authorities suggest testing for >3 months either after a new owner moves in, or by a seller before a home is listed.

What the science says:

Most Canadian Real Estate transactions from 2008-2018 occurred during warmer-weather months. In a survey of 776 short term tests, in 58.7% were inconclusive (meaning the result could not accurately predict whether a long term result was over or under 200 Bq/m3) in cold months, and 97% were inconclusive in warm months.   

Reference: Stanley et al. Radon exposure is rising steadily within the modern North American residential environment, and is increasingly uniform across seasons. In Press, 2019.