Mitigating Radon Gas in Century Homes: Key Strategies

Century homes are a beloved part of our architectural heritage. They offer timeless charm, intricate craftsmanship, and a deep sense of history. 

But with all their character comes a unique set of challenges, especially when it comes to indoor air quality. One of the most serious issues facing older homes today is radon gas infiltration.

At Peerless Air, we work with homeowners across Ontario to address radon issues effectively, especially in older homes where outdated construction practices often leave them more vulnerable.

Understanding how radon behaves in century homes—and how to mitigate it safely—is critical for protecting the structure and those living inside.

Why Century Homes Are Susceptible to Radon

Radon is a naturally occurring radioactive gas produced by the breakdown of uranium in soil and rock. It's invisible, odourless, and tasteless, but it can reach harmful levels when trapped indoors. 

According to Health Canada, long-term exposure to high levels of radon is a leading cause of lung cancer in non-smokers. Century homes were not built with modern air-sealing techniques or indoor air quality standards in mind. 

Their foundations are often made of stone, rubble, or early forms of concrete that lack vapour barriers or tight seals. Cracks in foundation walls, gaps around plumbing, and open crawl spaces all become entry points for radon gas.

Unlike newer homes that might be tightly sealed and easy to retrofit with modern mitigation systems, older homes can have unpredictable airflow, multiple additions, and complex structural issues that complicate radon control. That's where our experience comes in.

Professional Radon Testing

Before any mitigation steps can be planned, we start with accurate testing. We typically recommend a long-term radon test (90 days or more) for century homes, as this provides a more reliable picture of average exposure levels.

We use professional-grade equipment to monitor various points throughout the home, especially in basements and crawl spaces where radon entry is most common.

If test results exceed the Health Canada guideline of 200 Bq/m³, we will work with you to design a mitigation plan tailored to your home's unique structure.

Addressing Crawl Spaces and Earthen Floors

Many older homes have unfinished crawl spaces or even dirt floors, which can be significant sources of radon. These areas allow radon gas to rise freely into the living space. 

We often recommend installing a radon-resistant barrier over the soil, such as a heavy-duty polyethylene membrane, combined with a sub-membrane depressurization system to address this.

This technique involves laying down the membrane, sealing it to the foundation walls, and using a vent pipe with a radon fan to draw gas out from under the barrier and release it safely above the roofline. 

This system is discreet, highly effective, and minimally invasive—an important consideration when working in delicate historic homes.

Sealing and Reinforcing Foundation Walls

Stone or rubble foundations, common in century homes, are naturally porous and often cracked from age. We seal any visible gaps using radon-resistant caulking or hydraulic cement and may also apply a radon-blocking wall coating that helps reduce permeability.

We might install interior membrane systems where feasible to further isolate the living space from the foundation. These materials are carefully selected to preserve the home's structure while increasing its protection against soil gases.

Sub-Slab Depressurization

We often install a sub-slab depressurization system in homes with concrete basement slabs (even old ones). This is the most effective long-term radon mitigation method, and it involves creating a small suction point through the slab that connects to a fan-driven vent pipe. 

The fan continuously pulls radon from beneath the foundation and exhausts it safely outdoors.

This method is particularly effective when the slab is intact and combined with other air-sealing strategies throughout the basement.

Improving Ventilation Without Compromising the Home

Ventilation is another crucial tool in our radon mitigation approach. However, with century homes, we take great care not to disrupt the home's energy efficiency or historical integrity. 

Sometimes, we recommend an energy recovery ventilator (ERV) to help improve air exchange while maintaining comfortable indoor temperatures.

We also assess the pressure dynamics within the home, as older homes often suffer from unbalanced air flow that can pull radon inside. Correcting negative pressure zones and improving controlled ventilation can significantly reduce radon levels.

Ongoing Monitoring and Support

Mitigation is not a one-time job. We always follow up with post-mitigation testing to verify results and provide guidance on ongoing monitoring. 

We recommend annual testing or continuous radon monitors for century homes, especially after any renovation, landscaping, or structural work that could alter the home's air flow or foundation dynamics.

Trust Peerless Air for Specialized Radon Mitigation

Century homes deserve care and respect—and so do those living in them. We understand that historic properties come with unique challenges, and we approach each project with a combination of technical expertise and appreciation for heritage architecture.

If you suspect radon is affecting your older home, don't wait for visible signs—there often aren't any. Let us assess your property, provide reliable testing, and develop a customized mitigation strategy that preserves your health and your home's character.

Contact us today at Peerless Air to schedule a consultation. We're proud to help protect some of Ontario's most treasured homes while keeping families safe and informed.