Understanding Radon in Attached Houses: A Homeowner's Guide for York, PA

Why Attached Homes Present a Unique Radon Challenge

When I first moved to York, PA, I thought radon was something that only affected houses with basements and deep crawl spaces. A few years later, after helping a neighbor with her row home, I learned how wrong I was. The reality is that radon in attached houses behaves differently than in detached homes. Shared walls, common foundation slabs, and interconnected crawl spaces mean that one house's mitigation can affect the whole row, and one house's problem can become yours without you ever knowing it.

The Shared Foundation Problem

Attached houses share more than just walls. In many York neighborhoods built between the 1950s and 1980s, entire rows sit on a single poured concrete slab or a continuous crawl space. That common foundation means soil gas can travel laterally under the floor of one house and enter another through gaps or cracks. I have seen cases where a house sealed its own basement floor only to find radon levels rising because the gas was migrating from an adjacent unit where the slab was cracked.

This is the core issue with radon in attached houses: the mitigation system you install may be pulling soil gas from under your neighbor's home as well as your own. That is not necessarily bad, but it means you cannot assume that sealing cracks in your own floor will solve the problem. The gas has many paths, and shared foundations create a network of those paths.

Testing: The First Step Is Not as Simple as It Sounds

A standard home radon test kit placed in the lowest livable area works well for detached homes. With attached houses, you need to think about where the test goes. If you put it in a finished basement that is separated from the neighbor's unit by a thick firewall, you might get a reading that does not reflect the air you are breathing upstairs. I recommend testing on the ground floor as well, especially if the house is built on a slab. In York, the Pennsylvania radon levels vary block by block, so a single test is not enough. Test in at least two rooms, and test during the heating season when the stack effect is strongest.

Another thing I have learned: if you are in a row of attached houses and your neighbor tests high, you should test too. Even if your levels are low, the pressure differences between units can change over time. A neighbor's new mitigation system can alter airflow under your home and increase your indoor radon levels. That is not common, but it happens.

Mitigation Options for Attached Homes

The most effective radon reduction method for attached houses is sub-slab depressurization, but the installation has to account for the shared foundation. A typical system involves drilling a hole through the slab, pulling soil gas out with a radon fan, and venting it above the roofline. In an attached house, the fan must be sized correctly so it does not depressurize the neighbor's crawl space and draw more gas into their home. That is a real concern. A good radon contractor will perform a pressure field extension test to make sure the system works only under your house.

For houses with crawl spaces, foundation ventilation can be effective. Installing polyethylene sheeting over the dirt floor and sealing it to the walls creates a barrier that, combined with a vent pipe and fan, keeps soil gas from entering the living space. But in attached houses, the crawl space often runs the length of the row. You cannot just put plastic down in your section and call it done. The gas will move around the edges. You need to seal the plastic to the foundation walls and to any piers, and you may need to coordinate with neighbors to treat the entire crawl space. That is a bigger job, but it is the only way to get lasting results.

The Role of the EPA and Local Guidance

The EPA provides general guidance on radon mitigation, but their recommendations assume a single-family detached home. For attached houses, local knowledge matters a lot. In York, the housing stock includes many older row homes and duplexes where the original builders did not think about soil gas. The EPA's recommended action level of 4 pCi/L applies everywhere, but how you get below that level in an attached house can be different from the standard approach. I have seen mitigation systems that work perfectly in a detached home fail in an attached house because the system was not designed to handle the shared air pressure dynamics.

Sealing cracks and joints in the foundation is always a good idea, but it is rarely enough on its own. In attached houses, the cracks are often hidden behind shared walls or under floors that you cannot access. That is why a professional radon contractor who understands local construction is worth the investment. They know which York neighborhoods have slab-on-grade foundations and which have crawl spaces, and they know how to design a system that works within those constraints.

Practical Steps You Can Take

1. Test your home and your neighbor's home if possible. Radon in attached houses is a shared problem, and shared solutions work better.
2. If you find levels above 4 pCi/L, call a radon contractor who has experience with attached houses in Pennsylvania. Ask them about pressure field extension and shared foundation scenarios.
3. Consider a mitigation system that uses sub-slab depressurization or crawl space ventilation with proper sealing. Do not rely on sealing cracks alone.
4. Retest after mitigation to confirm the system is working and that it has not increased radon levels in adjacent units.

Long-Term Maintenance and Awareness

Once you have a mitigation system installed, it is not a set-and-forget solution. The radon fan needs to run continuously, and the system should be checked every few years. In attached houses, changes in the neighborhood can affect your radon levels. If a neighbor remodels or installs a new mitigation system, the pressure balance under your home can shift. That is not a reason to panic, but it is a reason to retest periodically.

I have also seen cases where a homeowner sealed their basement floor and installed polyethylene sheeting, only to find that the gas was entering through a shared wall cavity from the house next door. That is the nature of radon in attached houses. The problem is not confined to your property lines. The more you understand the shared structure, the better you can protect your home.

Final Thoughts

Living in an attached house in York, PA, comes with many advantages: walkable neighborhoods, shared maintenance costs, and a sense of community. But radon is one of those issues that requires a slightly different approach than what you read in national guides. The key is to test properly, work with someone who knows local construction, and think about the whole row, not just your unit. With the right mitigation system and a little awareness, you can keep your home safe and your family healthy. Do not let the shared foundation scare you off. It just means you need a smarter plan.