Answer to Question #11692 Submitted to "Ask the Experts"

Category: Environmental and Background Radiation — Radon

The following question was answered by an expert in the appropriate field:


I am in the process of purchasing a house which has recently had a radon test done by a home inspector. Our test came back with a reading of 4 picocuries per liter (pCi L-1) or about 150 becquerels per cubic meter (Bq m-3)*, which we were told is around the level of needing a mitigation system. We are trying to decide if that's absolutely necessary and we're hoping to get a second opinion from an educated professional.


I have been a professional dealing with residential radon since the 1980s, and I also had the experience of purchasing a home a few years back where the short-term levels measured slightly above 150 Bq m-3. I don't have the exact numbers but I remember the radon level being perhaps 170 Bq m-3. So you are going to get my experiences and thoughts during that process.

Note that measurements taken during the winter where the ground may be frozen tend to be higher than those taken at other times. While I was not particularly concerned about the potential health hazard at the measured level, I figured that down the line, when I wanted to sell the place, the new buyer was going to tell me to pay for fixing the radon levels.

Without knowing the actual level you are dealing with, I can suggest a few options for you depending on that level. Since my levels were low and I wanted the house, I offered to split the cost of mitigation with the sellers, which was roughly $800. They accepted and the cost was rolled into the closing costs. If the levels are above 4 pCi L-1 (about 150 Bq m-3),* the buyers have the right to insist on mitigation if they want to purchase. However, the seller has the right to refuse to do it, and you would lose the house!

If the level is just below 4 pCi L-1 (about 150 Bq m-3),* your options are reduced because the seller has no obligations according to most contracts. However, you might consider asking them to put possible mitigation costs into an escrow account. The funds would only be used if the results of a long-term radon measurement (typically one year) indicated the need. You might find sellers reluctant to do that, however. Note even if the levels are above the magic number of 4 pCi L-1 (about 150 Bq m-3),* you might make that offer.

Phil Kearney, PhD

* The radon concentration units are given here in pCi L-1 (called traditional units) because that is the unit used by the Environmental Protection Agency. However, the Health Physics Society has adopted the SI (International System) of units and these are given afterwards.

Ask the Experts is posting answers using only SI (the International System of Units) in accordance with international practice. To convert these to traditional units we have prepared a conversion table. You can also view a diagram to help put the radiation information presented in this question and answer in perspective. Explanations of radiation terms can be found here.
Answer posted on 5 August 2016. The information posted on this web page is intended as general reference information only. Specific facts and circumstances may affect the applicability of concepts, materials, and information described herein. The information provided is not a substitute for professional advice and should not be relied upon in the absence of such professional advice. To the best of our knowledge, answers are correct at the time they are posted. Be advised that over time, requirements could change, new data could be made available, and Internet links could change, affecting the correctness of the answers. Answers are the professional opinions of the expert responding to each question; they do not necessarily represent the position of the Health Physics Society.