We often receive emails or phone calls from CERTI students who are challenged by clients when they are asked to maintain closed house conditions when a short-term radon test is performed.  After all, to a homeowner it seems like an unnatural requirement and a condition that would increase radon levels to where mitigation is warranted at the time of sale of a property.

We also see websites of measurement companies state that closed building conditions are required by protocols period as if that should satisfy any doubts a homeowner may have.  Although it is true that measurement protocols do state this, it would be good to be able to explain the rationale behind this requirement.

First there are two basic testing approaches:  Short-term and long-term.  Short-term measurements obtain a radon average over a minimum 2-day period up to 90 days, where closed building conditions would be required.  Long-term measurements obtain an average radon measurement over a longer period with a minimum duration of 91 days, up to a full year, but without closed building requirements.  So, what is the purpose of either of these approaches?

Short-term measurements are designed to determine the radon potential of the home independently of how an occupant operates the home.  They are not designed to determine the actual exposure to radon.  In the early days of radon (1980s), these were referred to as “screening measurements.”  The purpose of a screening measurement was to quickly identify potential radon concerns which, if found to be elevated, would be followed up with additional, confirmatory measurements.  The follow-up measurements recommended would often be long-term measurements to determine actual exposure.

Fast forward to the 1990s when testing at the time of real estate transactions was encouraged.  Few homeowners or real estate agents wanted to defer resolution of a contract contingency with a 91 plus day test.  Consequently, it became the norm to resolve radon contingencies in purchase agreements with a quick 2-3 day test, aka Short-Term test requiring closed building conditions.  

In explaining the purpose of closed building conditions, it is good to relay what the results will mean.  When performing a short-term test or screening measurement it is conducted in a manner to maximize the results of tests conducted in living spaces (not crawlspaces).  Accordingly, we place the device in the lowest occupiable level where the radon is expected to be the highest because that is where it comes in before being diluted on upper levels with outside air.  We also close windows and doors other than momentary entrance and exit.  Under these conditions (and here is the key element) if the radon measurement is less than 4.0 pCi/L, one can say with reasonable confidence that radon levels on upper floors and under normal lived-in conditions will also be less than 4.0 pCi/L. 

Bottom line: Short-term tests indicate radon potential of the home.  Their results do not indicate actual exposure to an occupant as they live in multiple levels and with open windows and patio doors.  

Caution:  Be careful not to say that the result of a short-term test is a “worst case scenario” or that radon levels will never be higher than results from a short-term test.  Although we attempt to drive up radon levels by testing the home and maintaining closed building conditions, we cannot control the weather and the operation of HVAC systems.  Several studies have shown in homes with radon levels around 4 that on any two-day test period the result can be either above or below 4, even under carefully controlled conditions.  Here is a phrase that might work for you:

The results of this test reflect the environmental conditions and how the building was operated during the period of the measurement.  

The results indicate the radon potential for this home.  If the results are less than 4.0 pCi/L, it is advised the home be retested in the future to verify continued levels less than 4.0 pCi/L.

How about just closing the windows in the room where the test device is located?

Often a homeowner may whine or cheat a little by opening a window in another part of the house than where you placed the measurement device.  Closed building conditions refer to openings in the shell of the building.  An open window anywhere on the shell will reduce the negative pressures throughout the building and reduce radon entry.  So, closing the door to the room where your test device is located but opening windows in other rooms doesn’t cut it.  

To illustrate this, CERTI conducted a test in a home that had a relatively high radon potential.  A continuous radon monitor was deployed in one room and after a day a window in the same room was partially opened.  Then the window was closed and after the measurements re-equilibrated a similar window located at the opposite end of the basement was opened to the same amount as the first one.  The graph below shows the effect on the measurement device when each of the windows were individually opened.  

As you can see, opening a window in the same room as the device or opening one 25 yards away on the opposite end of the basement had a significant impact.  So, as you might be inclined to be a little forgiving, you can see the impact of not following protocols and the need to fully explain the need for compliance.  Granted, you may not be able to detect such deviations, but that is why having a homeowner instruction sheet or agreement as well as the using the suggested language above makes sense.

Who said there was nothing new in Radon?

Doug Kladder
Technical Consultant to CERTI