What is Radon?

Radon is an odorless, heavy, radioactive gas that comes from the breakdown of uranium in the rock and soil beneath us. Because uranium is deposited throughout the Earth’s crust, radon is all around us, all the time. The average outdoor radon concentration is 0.4 pCi/L. The national average indoor radon concentration is about 1.3 pCi/L. The EPA recommends remediation when the level reaches 4 pCi/L or more. Radon seeps into our homes through cracks and crevices in foundation walls, through soil in crawlspaces, and through cracks or openings in concrete floor slabs. The concentration of radon can fluctuate quite a bit throughout the year and depends on the weather conditions and various conditions in the home.

Radon levels are measured in pCi/L, which is “Picocurie Per Liter.” A curie is a unit of measure for radioactivity that is equivalent to 1 gram of radium.

Why is radon testing important?

Prolonged exposure to radon gas is known to cause lung cancer. In fact, it is considered the second leading cause of lung cancer next to smoking. Roughly 22,000 U.S. deaths per year are attributed to radon exposure. So, it is important to test for radon in order to remediate the problem if necessary and protect your family.

Is radon testing in Montgomery County, MD required by law?

The answer is YES, but only for real estate transactions that do not involve multi-unit buildings such as condominiums. There are also four areas exempt from the Montgomery County radon law. Those areas are:

  • Kensington
  • Rockville City
  • Poolesville
  • Barnesville


A few other exemptions apply and can be found at: https://www.montgomerycountymd.gov/green/Resources/Files/air/Radon-Handout.pdf.

Remember, it is still recommended that homes be tested in exempt areas. Radon does not discriminate!

How does one remediate radon?

Typically, a 4” PVC pipe is inserted below the lowest floor slab, in a sump pit, or under a vapor barrier in a crawlspace. The pipe is extended through the house and roof, or it is directed outside through a wall penetration and then extended above the roof line. A quiet fan is installed in-line with the pipe at the exterior or in the attic and runs continuously. This causes negative air pressure under the slab or vapor barrier which draws the radon gas into the pipe and pushes it outside above the home. Radon remediation typically costs between $800 and $1200 and is usually very effective at reducing radon levels below 4 pCi/L.

Can TTBS perform Maryland radon testing?

YES! We can also perform radon testing in Virginia and D.C.. West Virginia radon testing is coming soon.

How does TTBS perform a radon test?

First, Top To Bottom Services is proud to say we have an employee on staff with a radon certification through the National Radon Proficiency Program (NRPP). This person manages our NRPP radon certified laboratory and oversees the deployment, pickup, and analysis of all of our radon tests in conformance with the strict quality control standards set forth by the NRPP. This ensures the most accurate and reliable radon testing results.

We use a passive radon testing method with E-Perm electret pods. These pods are enclosed in a small black box which we place in the lowest livable space of your home, the living space over a crawlspace, or the living space over a slab on grade, as per EPA testing protocols. The electrets are positively charged and deplete in charge as they are exposed to radon radiation. We read the before and after results, factor in the length of deployment, and perform a calculation to determine the average radon concentration during the testing period. For real estate transactions, the testing period is a minimum of 48 hours.

NOTE: It is important to maintain closed-house conditions during the test. For more information about radon testing, please visit:


When do I need to test for radon?

The EPA recommends testing during every real estate transaction, after remediation, every 1-3 years, and any time conditions in the home change (ie: new windows are installed, renovations are performed that affect air flow, a crawlspace is closed or opened, a new HVAC system is installed, a basement drainage system is installed, etc.)

Do I need a professional with a radon certification to test, or can I use a test kit from the big box store?

Well, chances are, if you are still reading at this point, you probably don’t have the knowledge necessary to perform a very reliable and accurate test. Whether it’s TTBS or another company, we always recommend you use a qualified radon professional to perform your test. It costs a bit more, but in the long run, the health costs to you and your family can be much worse if the test is inaccurate!

Contact one of our client coordinators to schedule a radon test, or if you would like more information about radon, please contact our ancillary services manager, John Overholser, at 301-938-9100 x226.