January 13, 2026

Radon Mitigation in Ottawa: How to Fix High Radon Levels in Your Home

Learn how radon mitigation works in Ottawa homes. Discover Active Soil Depressurization, what to expect during installation, post-testing requirements, and how to choose a contractor.

Your radon test came back elevated — above Health Canada’s 200 Bq/m³ guideline. Now what? The good news is that high radon levels are fixable. Radon mitigation is a proven solution that can reduce radon concentrations by 90% or more in most homes, and installation is often completed in a single day. This guide explains how the mitigation process works, what to expect during installation, post-mitigation testing requirements, and how to choose a qualified contractor for your Ottawa home.

What Is Radon Mitigation?

Radon mitigation is the process of installing a system to actively reduce radon gas entering your home from the ground. The most effective method — and the one recommended by the National Standard of Canada — is called Active Soil Depressurization (ASD).

ASD works by changing the pathway that radon takes. Instead of seeping through cracks in your foundation and accumulating in your basement, radon is captured and expelled safely to the outdoors where it is rapidly diluted to harmless levels.

The result: after a properly installed ASD system runs, many homes achieve radon levels comparable to outdoor air (typically 5–15 Bq/m³).

How Active Soil Depressurization Works

An ASD system operates on a simple principle: creating negative pressure beneath your foundation to prevent radon-laden soil gas from entering your home.

Here’s the step-by-step process:

1. Diagnostic Testing Before installation, a certified mitigation professional conducts diagnostic tests. This typically involves drilling a couple of small holes in the far corners of your foundation slab and measuring pressure changes in the soil. This information tells the contractor how much negative pressure is needed and where the best location is for the system.

2. System Design Based on the diagnostic results, the professional designs a customized system. This includes determining the fan size, the optimal suction point location, and the best route for the exhaust pipe.

3. Sealing Entry Points Before the fan is activated, all primary radon entry points are sealed. These include foundation cracks, gaps around pipes and utilities, sump pump lids, and floor-to-wall joints. Sealing is a prerequisite for effective mitigation — it directs radon toward the controlled pathway created by the ASD system.

4. Installation The installation involves:

  • Drilling a suction point through the foundation slab into the soil gas collection layer
  • Installing a soil gas collection plenum (the pathway that draws radon-bearing soil gas from beneath the slab)
  • Running a pipe from the suction point to an exterior discharge location
  • Installing the exhaust fan in the pipe
  • Installing a permanent label on the system to identify it for future referenceIn Ottawa’s cold climate, the CGSB national standard favours a side-wall discharge — a short pipe exiting through the exterior wall near ground level — as it avoids freeze-related issues associated with roof penetrations. The discharge location must maintain minimum clearance distances from windows, doors, and air intakes as specified in the CGSB standard.5. System Operation Once the fan is running, it continuously draws radon-laden soil gas from beneath your home and exhausts it outdoors, where it is rapidly diluted to harmless levels. The system maintains negative pressure under the slab at all times to prevent radon from entering the building.Additional Benefits: Beyond radon reduction, ASD systems often lower basement humidity and reduce the entry of other soil gases.

The CGSB National Standard: What It Means

The Canadian General Standards Board (CGSB) publishes the National Standard of Canada for radon mitigation: CAN/CGSB-149.12-2024. This standard, published in September 2024 in Ottawa, represents the definitive national guidance for radon mitigation in existing buildings.

Key points from the standard:

  • ASD is the preferred method, with demonstrated reductions of approximately 90% or more in indoor radon concentrations
  • Sealing of entry points is a prerequisite — all cracks, gaps, and openings where radon can enter must be sealed as part of any mitigation approach
  • Proper design and installation are critical — systems must be designed by qualified professionals following specific technical protocols
  • Post-mitigation testing is required to verify the system is working
  • ALARA principle applies — radon levels should be reduced to As Low As Reasonably Achievable, targeting the Health Canada guideline of 200 Bq/m³ at minimumWhen you hire an Ottawa radon mitigation professional, they work to this national standard — it ensures consistency and effectiveness across Canada.

When to Mitigate: Ottawa Public Health Action Timelines

Before scheduling mitigation, it’s helpful to understand Ottawa Public Health’s recommended action timelines based on your radon level:

Radon LevelRecommended Action
Above 600 Bq/m³Remediate within one year
200–600 Bq/m³Remediate within two years

These timelines give you a window to plan and schedule your mitigation. If you’re in the upper range (above 600 Bq/m³), prioritizing mitigation sooner is wise. Either way, the process itself — once you schedule it — can be completed in a single day.

What to Expect During a Mitigation Job

Timeline: Most homes can be mitigated in a single day. The time required depends on your home’s foundation type and complexity, but the entire process — diagnostics, installation, and system activation — is completed in a single day.

The Installation Process:

  • The contractor will conduct diagnostic pressure tests (20–30 minutes)
  • Small holes are drilled in the foundation slab (minimal and easily repaired later)
  • The soil gas collection system is installed
  • The exhaust pipe is run (usually inside the building to avoid winter freeze issues in Ottawa’s cold climate)
  • The fan is installed and tested
  • All entry points are sealed
  • The contractor provides you with system documentation and explains how to monitor itDisruption: The process is relatively non-invasive. Drilling creates some dust, and there will be some noise, but the system is designed to integrate into your home with minimal visual impact.Cost Note: Mitigation costs vary based on foundation type, home size, and system complexity. Rather than quoting generic figures that quickly become outdated, discuss pricing directly with your contractor.

Post-Mitigation Testing: Short-Term and Long-Term

Once your mitigation system is installed, testing confirms that it is working effectively.

Short-Term Test (Verification Test)

  • Conducted after the fan has run for at least 24 hours
  • Minimum duration: 48 hours
  • Uses a professional continuous radon monitor or digital device
  • Confirms the system is reducing radon immediately
  • Result: You’ll know within days if the system is workingLong-Term Test (Confirmation Test)
  • Conducted during the following heating season (October–March in Ottawa)
  • Duration: minimum 91 days (3 months), ideally longer for accuracy
  • Captures seasonal variation and provides your true annual average radon level
  • Uses a passive or digital deviceOngoing Monitoring
  • Repeat long-term testing at least every 5 years to confirm the system remains effective
  • More frequent testing may be recommended if you want continuous visibility into your radon levelsIf using a digital radon monitor for post-mitigation testing, reset the device after the fan is turned on so the readings reflect the post-mitigation period only.

Questions to Ask Your Mitigation Contractor

Before hiring a radon mitigation professional, make sure you understand their qualifications and approach:

  • Proof of experience: Ask for references and photos of past work in Ottawa homes
  • Insurance coverage: Verify they carry liability insurance
  • System design: Request a clear explanation of the system design, including where the suction point will be located and how the pipe will be routed
  • Warranty: Ask about any warranty on their work and the system components
  • Post-mitigation testing plan: Confirm they provide or arrange the 48-hour short-term test to verify the system is working

FAQ

Q: How much does radon mitigation cost? A: Mitigation costs vary based on foundation type, home size, and system complexity. Contact local contractors for quotes. Costs have historically ranged widely, so get multiple estimates to understand the fair price in your area.

Q: How long does the installation take? A: Most homes are mitigated in a single day. The exact timing depends on your home’s foundation type and complexity. You can usually return to normal home use immediately after the work is complete.

Q: Will the mitigation system be noisy? A: ASD fans are generally quiet during operation. Properly installed systems are mounted with vibration dampeners to minimize sound. Most homeowners report they quickly become accustomed to the gentle hum, similar to a refrigerator.

Q: How long does an ASD fan last? A: ASD fans are designed for continuous duty and typically last 10–15 years before needing replacement. Your contractor can advise on maintenance and when eventual replacement may be needed.

Q: What if my short-term test shows the system isn’t working? A: This is rare with a properly installed system, but if it happens, the contractor can troubleshoot the issue. Common problems (like a blocked exhaust pipe or fan failure) are quickly identified and corrected.

Q: Do I need to do anything to maintain the system? A: ASD systems are low-maintenance. The fan runs continuously and requires no regular upkeep. Ensure the exhaust outlet remains clear of debris or snow (especially important in Ottawa winters).

Q: Can I test my radon levels myself after mitigation? A: Yes. You can use a digital radon monitor to track your levels, or order a passive test kit for an independent measurement. Many homeowners use digital monitors to maintain peace of mind long-term.

Q: Do I really need a professional to install the system, or can I do it myself? A: Radon mitigation requires specialized knowledge of foundation dynamics, soil gas behaviour, and proper system design. Health Canada and the national CGSB standard recommend hiring a qualified professional. A professional’s diagnostic testing ensures your system is sized correctly and installed to maximize radon reduction — and most offer a warranty on their work. This is not a DIY project.

Q: What if the long-term post-mitigation test shows radon levels are still elevated? A: This is rare when systems are properly designed and installed, but if it occurs, your contractor will investigate potential causes (e.g., unsealed entry points, system performance issues) and make adjustments. The system will be retested until it achieves the target radon reduction.

Ready to Fix Your Radon Problem?

High radon levels are one of the few home hazards that are both clearly identifiable through testing and completely fixable through professional mitigation. If your test results came back above 200 Bq/m³, the next step is straightforward: contact an experienced mitigation professional to discuss your options.

Ottawa Radon Expert is a trusted local team with extensive experience designing and installing radon mitigation systems in Ottawa homes. We follow the national CGSB standard, provide a post-mitigation warranty on every installation, and ensure your system is properly tested and documented. Our goal is to give you and your family confidence that your home’s air is safe.

Contact Ottawa Radon Expert today to schedule your mitigation consultation and take control of your radon levels.

Internal links: Learn more about how to test for radon or radon levels in Ottawa.

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