Understanding Radon in Attached Houses: What Homeowners in York, PA Need to Know

Why Attached Houses Have Their Own Radon Risks

When people picture a house with a radon problem, they often think of a detached single-family home with a basement. But in older towns like York, PA, the housing stock includes plenty of rowhomes, duplexes, and townhouses. These attached houses share walls and sometimes share a foundation or crawl space with a neighbor. That changes how soil gas moves and where radon enters the living space. I have seen homeowners in York assume that because their unit is on the second floor or above grade, they are safe. That belief can lead to missed warning signs and higher radon levels than expected.

Radon comes from the natural decay of uranium in soil and rock. It seeps upward through the ground and enters buildings through cracks in the slab, gaps around pipes, and openings in the foundation. For an attached house, the pathways are not limited to your own footprint. Gas can migrate horizontally through the soil under the row and enter through a neighbor's basement wall, then travel through shared structural spaces. Understanding radon in attached houses means understanding that your exposure is tied to the entire building envelope, not just your unit.

How Attached Construction Changes the Picture

In a detached home, the mitigation strategy usually focuses on the slab and the perimeter of the foundation. In an attached house, you may share a party wall, a common crawl space, or even a continuous basement floor with the next unit. That shared infrastructure creates multiple entry routes for radon. For example, if your neighbor has a sump pump pit or a floor drain that connects to the soil below, radon can enter their space and then move through wall cavities or ductwork into yours. I have seen cases in York where one unit tested at 2 picocuries per liter while the unit next door tested at 8. The difference came from a hidden crack in the shared foundation wall on the higher side.

Radon testing in attached houses must account for these shared pathways. A single test in one unit does not tell you the full story. The EPA recommends testing every unit in a multi-unit building, ideally at the same time. If you live in an attached house, you should test your own unit and talk to your neighbors about testing theirs. A home radon test kit is inexpensive and easy to use. Place it in the lowest livable area of your unit, usually the basement or first floor if there is no basement, and follow the kit instructions carefully.

Where Radon Enters in an Attached House

The soil gas that carries radon is pulled into a house by the pressure difference between the indoor air and the outdoor air. In attached houses, the pressure dynamics are more complex because the whole row acts like one large building. The stack effect can draw air up through shared stairwells or elevator shafts in larger townhouse complexes. In a typical York rowhome, the most common entry points are:

• Cracks in the basement floor slab or the slab under a crawl space
• Gaps around utility penetrations like water pipes and gas lines
• Openings in the foundation wall where it meets the floor joists
• Unsealed sump pumps or floor drains
• Mortar joints in brick or block foundation walls that have deteriorated over time

Sealing cracks and other openings is a critical first step in radon reduction, but it is rarely enough by itself. In attached houses, the shared structure means that sealing only your side may leave pathways open from the neighbor's side. A comprehensive approach requires coordination and sometimes a mitigation system that covers the whole building.

Mitigation Strategies That Work in Attached Houses

Radon mitigation in attached houses follows the same basic principles as in detached homes, but the installation details differ. The most common system is sub-slab depressurization. A pipe runs from below the basement slab through the wall to a radon fan that vents the soil gas above the roofline. The fan creates a low-pressure zone under the slab, so soil gas is pulled into the pipe and exhausted outside rather than entering the house. In a row of attached houses, the sub-slab system often needs to be installed in each unit separately because the slabs are not continuous across party walls. But in some older constructions, there is a continuous gravel bed under the entire row. In that case, a single fan might affect multiple units, which makes installation more complex and requires careful testing.

For houses with a crawl space instead of a full basement, the approach is similar but uses polyethylene sheeting laid over the dirt floor. The edges are sealed to the foundation walls, and a vent pipe is installed through the sheeting to the outside. A radon fan pulls the gas from under the sheeting and vents it away. I have seen crawl space installations in York where the sheeting was poorly taped at the seams, allowing soil gas to leak into the living space above. Proper sealing is essential, especially in attached houses where the crawl space may extend under multiple units.

Foundation ventilation is another option, but it is less common in Pennsylvania because of the cold winters. Ventilating the crawl space or basement with outside air can dilute radon levels, but it also increases heating costs and can introduce moisture problems. A dedicated mitigation system with a radon fan is usually more effective and more energy efficient.

The Role of Professional Help

Radon testing is something any homeowner can do. But once the test results come back high, the next step often requires a radon contractor. In York, PA, there are experienced contractors who understand the local housing stock and the geology of the area. The Pennsylvania radon problem is well documented, and the state has some of the highest average radon levels in the country. A good contractor will perform a diagnostic test to measure the pressure across the slab and identify the best location for the suction point. They will also check for radon entry through the walls if you share a foundation with a neighbor.

When hiring a radon contractor, ask about their experience with attached houses. Not all contractors are used to the shared-wall scenario. Some may try to install a system that works for a detached house without considering the pathways through the party wall. A contractor who understands radon in attached houses will take the time to inspect the neighbor's side if possible, or at least account for the shared structure in their design.

Long-Term Maintenance and Monitoring

Once a mitigation system is installed, it needs regular checks. The radon fan should run continuously, and the pressure indicator should be monitored to make sure the system is working. In attached houses, a fan failure in one unit can affect radon levels in the adjacent unit because the pressure balance changes. I recommend that homeowners in attached houses test their radon levels at least every two years, even after mitigation. The EPA also suggests testing after any major renovation, especially if it involves the foundation or the floor slab.

Polyethylene sheeting in crawl spaces can degrade over time, and the tape seals can fail. Sealing cracks in the slab is a maintenance item, not a one-time fix. The mortar in old foundation walls can crumble, opening new pathways for soil gas. In attached houses, any maintenance that affects the building envelope should be done with the awareness that it could change radon entry patterns. A neighbor's renovation can inadvertently create new pathways into your unit, so communication between owners is valuable.

Final Thoughts for Homeowners in York

Living in an attached house in York, PA, means you are part of a shared structure with shared risks. Radon is a serious health concern, and it is the leading cause of lung cancer after smoking. The good news is that radon levels can be reduced. Testing is the first step, and it gives you the information you need to decide whether mitigation is necessary. If your test result is above 4 picocuries per liter, the EPA recommends taking action. For attached houses, that action may need to be coordinated with your neighbors, but it is worth doing.

Radon in attached houses is a topic that deserves more attention than it gets. Too often, owners of rowhomes and townhouses assume the risk is lower because they are not on the ground floor. That assumption is false. The soil gas can enter anywhere there is a gap in the building envelope, and in attached houses, those gaps can be shared. By understanding the unique pathways and working with a knowledgeable radon contractor, you can protect your home and your health. The investment in radon mitigation is small compared to the peace of mind it provides.