The planning list for a finished basement fills up quickly: flooring, lighting, where the television goes, whether there is room for a bathroom. One item that deserves to be near the top is almost never on it, because it cannot be seen, smelled or heard. It costs a few dollars to check, and the answer can change how the floor and walls are built.
The item is radon, and the time to test for it is before the first stud goes up.
What radon is and why basements matter
The Fairfax County Health Department describes radon as a natural, radioactive gas that is colorless, tasteless and odorless. It forms as uranium in rock and soil breaks down, and it seeps into buildings through foundation cracks, basement walls and gaps around pipes and sump pumps. The department cites the U.S. Surgeon General's advisory that radon is the second-leading cause of lung cancer in the United States.
Because it comes up from the ground, the lowest level of a house generally has the highest concentration. An unfinished basement used for laundry and storage exposes nobody for very long. Turn it into a family room, a home office or a bedroom and people will spend hours a day in that air.
The local picture
This is not a remote risk here. The Environmental Protection Agency classifies Fairfax County as Zone 1, its highest category, and the county's health department puts it in one sentence: homes in Fairfax County are at a high risk for indoor radon. That takes in the communities with Alexandria addresses in the county's southeastern corner as well as everything to the west.
A zone map only describes averages. Two houses on the same street can test very differently, depending on the soil under each slab and how each foundation was built. The department's position is that testing is the only way to know for sure whether a house has a problem.
Testing is cheap and simple
Test kits are sold at hardware and home improvement stores, and a qualified tester can be hired to do it instead. Virginia residents can also order a kit for $3 through the Virginia Department of Health's radon program at vdhradon.org, according to the county.
A few points make the result more useful:
- Place the test in the basement itself, in the part you plan to finish.
- Follow the kit's instructions about closed windows and doors, and about how long to leave it.
- Do it early. If the result leads to changes in the design, you want to know before the drawings are final.
Reading the number
Results are reported in picocuries per liter, written pCi/L. The EPA recommends fixing a home when the level is at or above 4 pCi/L. Because there is no known safe level of exposure, the agency also suggests that people consider fixing their homes at levels between 2 and 4.
A high reading is not a reason to abandon the project. It is a reason to add one line to the scope.
Why before, and not after
The county's summary of the fix is that a mitigation system is installed to remove the radon gas from beneath the home. In practice that means collecting the gas under the slab and piping it outdoors, with a fan to keep it moving. The pipe has to run from below the floor to above the roofline or out through the wall.
In an unfinished basement, routing that pipe is easy. The slab is bare, the walls are open and the installer can choose the shortest, least visible path. Cracks in the floor and the gap around the sump can be sealed while they are still accessible. In a finished basement the same work means cutting through new flooring, opening a new wall or boxing a pipe into the corner of a room that was designed without it.
Knowing the result first also lets the designer plan around the system: a chase beside the mechanical room, a sump with a sealed lid, an outlet where the fan will need one.
Test again when the room is done
Finishing a basement changes the way air moves through the house. New walls, a tighter door at the top of the stairs and changes to heating and cooling can all shift the radon level in either direction. A second test once the room is in use confirms that the level is where it should be, and a further test every few years is a sensible habit.
Where this sits in the larger plan
Radon belongs with the other conditions that have to be right before the finishes matter: a dry slab, enough headroom and a safe way out. It is one of several factors that make two basements of the same size cost different amounts to finish. The full list of those factors, with the layout and lighting decisions that follow them, is set out in What Finishing an Alexandria Basement Involves: Cost Factors, Planning and Layout Ideas.
Two other articles on this site are useful background for the design stage: a guide to renovating with the architecture of the house in mind, and a piece on choosing bathroom fixtures, which is relevant if the basement plan includes a bath.
Raising it with your contractor
A contractor who finishes basements regularly should be comfortable with the question and able to build the routing for a mitigation system into the plan. Vale Construction is a design-build remodeling company and general contractor in Alexandria, founded in 2005, that lists basement finishing among its services. The company holds a Virginia Class A contractor license and carries general liability and workers' compensation insurance on its jobs.
Directions to Vale Construction from Wilton Woods Center
Wilton Woods Center, a Fairfax County Public Schools facility on Franconia Road, is a convenient place to start. The map shows the drive from there to the office on Alexander Avenue.
Vale Construction
6020 Alexander Ave
Alexandria, VA 22310
(571) 474-1920
Common radon questions
My neighbor tested low. Do I still need to test?
Yes. Levels vary from house to house, and only a test in your own basement tells you about yours.
Does a newer house need testing?
Age is not a reliable guide. New and old houses can both have elevated levels.
Will sealing the floor solve it on its own?
Sealing helps a mitigation system work, but the county describes the fix as a system that removes the gas from beneath the home. Ask a qualified mitigation professional what your house needs.