What is Health Canada's radon guideline for homes?

Health Canada's guideline recommends remedial action when the average annual radon concentration in the normal occupancy area of a home exceeds 200 becquerels per cubic metre. Below 200 Bq/m3, no action is required, though Health Canada notes there is no known safe threshold and lower is always better. Between 200 and 600 Bq/m3, remedial action should be taken within two years. Above 600 Bq/m3, remedial action should be taken within one year. Testing should be done for a minimum of 3 months, ideally during fall or winter when windows are closed and radon levels are typically highest.

How does sub-slab depressurization reduce radon?

Sub-slab depressurization (SSD) works by creating negative pressure beneath the foundation slab relative to the indoor air pressure. A pipe is inserted through the slab into the soil or aggregate layer below, connected to an inline fan that continuously extracts soil gas and vents it above the roofline. This negative pressure field prevents radon-laden soil gas from entering the building through the slab, cracks, and other penetrations, since air now flows into the soil from the house rather than the reverse. A properly designed system achieves negative pressure across the entire slab area, not just near the extraction point, which is why pressure field extension testing is a critical step in system design.

How do I size a radon mitigation fan?

Fan sizing depends on the required airflow to maintain negative pressure across the slab area and the static pressure the fan must overcome, which is determined primarily by soil permeability. Highly permeable soils like gravel or coarse sand require higher airflow but lower pressure. Low-permeability soils like clay require lower airflow but the fan must generate higher static pressure to achieve pressure field extension through the less porous material. A single suction point typically covers 465 to 930 square metres of slab area in permeable soil, but may only extend 90 to 230 square metres in low-permeability clay, sometimes requiring multiple suction points for larger foundations.

Is radon mitigation required by Canadian building code?

The National Building Code of Canada requires a rough-in for future radon mitigation in new residential construction, meaning a passive vent pipe from beneath the slab to outside the building, capped and ready for a fan to be added if testing later reveals elevated radon. This rough-in requirement does not mean every new home has active radon mitigation from the start; it means adding a fan later, if needed, is straightforward and inexpensive rather than requiring slab penetration after the fact. Existing homes built before this requirement, or without the rough-in, require full retrofit installation including slab penetration if testing reveals radon above the Health Canada action level.

🔙 Pollutants

Radon Mitigation Calculator

Calculate sub-slab depressurization fan sizing for radon mitigation. Estimate airflow and pressure field extension from foundation type and soil permeability. Uses Health Canada's 200 Bq/m³ guideline.

🔙 Current Radon Level

Measured Radon Level i

Bq/m³

Target Reduction Level

Bq/m³

🏜 Soil / Sub-Slab Material

🏠 Foundation Details

Total Slab Area i

m²

Foundation Type

Sump Pit Present?

🔙 Radon Mitigation Results

Current Radon Level vs. Health Canada Guideline

Suction Point Coverage & System Sizing

Full Results Table

Parameter	Value	Notes

Export:

How to Use This Calculator

Enter Your Measured Radon Level

Use the long-term average from a certified radon test, ideally 3 months or longer during fall or winter. Set your target reduction level — commonly 100 Bq/m³ or lower, well under the 200 Bq/m³ Health Canada action level.

Select Sub-Slab Material

Soil and sub-slab aggregate permeability is the single biggest factor in system design. Gravel and coarse aggregate allow one suction point to cover a large area at low fan pressure. Clay requires higher pressure and often multiple suction points.

Enter Foundation Details

Total slab area, foundation type, and whether a sump pit is present all affect system design. A sump pit is often the easiest and most effective suction point location when present, since it already provides an opening to the sub-slab area.

Review Fan Sizing and Suction Points

The results show estimated coverage area per suction point, number of suction points needed for your slab area, and fan airflow and pressure requirements. Actual fan selection should be verified with pressure field extension testing after installation.

Radon Mitigation in Canadian Homes: System Design Fundamentals

Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil and rock, present to some degree beneath virtually every home in Canada. It seeps into buildings through foundation cracks, sump pits, and other openings, and because it's odourless and invisible, testing is the only way to know if levels are elevated. Health Canada estimates radon exposure causes approximately 3,000 lung cancer deaths in Canada annually, second only to smoking as a cause of lung cancer.

How Sub-Slab Depressurization Works

The most effective and common radon mitigation approach is active sub-slab depressurization (ASD). A pipe penetrates the foundation slab into the soil or aggregate beneath, connected to a continuously running inline fan that exhausts to above the roofline. This creates negative pressure in the sub-slab region relative to the house, reversing the natural pressure gradient that draws radon-laden soil gas indoors. Instead, air is drawn from the house into the soil at a low rate, and radon gas is vented directly outside before it can enter the living space. The system doesn't remove radon from the soil; it prevents the soil gas pathway into the building.

Soil Permeability and System Design

The permeability of the material beneath the slab determines how far the negative pressure field extends from a single suction point, and therefore how many suction points a system needs. In homes with a proper 100mm to 150mm layer of clean gravel or crushed stone beneath the slab (increasingly standard in new Canadian construction), a single suction point can achieve pressure field extension across 465 to 930 square metres. In homes with native soil, sand, or fill directly beneath the slab, coverage drops significantly, sometimes to under 100 square metres per suction point in dense clay conditions. This is why radon mitigators perform pressure field extension (PFE) testing after installing a temporary suction point, drilling small monitoring holes at increasing distances to measure at what point the negative pressure becomes too weak to be effective.

Fan Selection and Static Pressure

Radon fans are specified by two performance curves: airflow at zero static pressure, and static pressure at zero airflow (the fan's maximum "stall" pressure). Systems in permeable soil need fans that can move higher airflow at relatively low pressure. Systems in tight clay soil need fans that can generate high static pressure even at low airflow, since the resistance to air movement through the dense soil is the limiting factor. Undersized fans in tight soil conditions fail to achieve adequate pressure field extension, leaving portions of the slab unprotected even though the system appears to be running. This is a common cause of radon mitigation systems that don't achieve the expected reduction.

Multiple Suction Points and Complex Foundations

Larger homes, homes with multiple foundation types (a basement combined with an attached garage slab, for example), or homes with interior footings that create isolated sub-slab zones often require multiple suction points connected to a single fan through a manifold, or in some cases multiple independent fan systems. Each isolated sub-slab area needs its own pressure field coverage — a suction point in the main basement typically cannot achieve adequate depressurization under a separate slab section isolated by a interior footing or foundation wall extending to the aggregate layer.

National Building Code Rough-In Requirements

The National Building Code of Canada requires new residential construction to include a rough-in for future radon mitigation: a vent pipe from beneath the slab, routed through the building, and capped at both ends, ready for a fan to be added if post-occupancy testing reveals elevated radon. This rough-in dramatically reduces the cost and disruption of adding active mitigation later compared to a full retrofit that requires slab penetration after the home is finished and occupied. Homeowners in new construction should verify the rough-in location and test for radon in the first year of occupancy to determine if fan activation is needed.

Frequently Asked Questions

Health Canada recommends remedial action when the average annual radon concentration in normal occupancy areas exceeds 200 Bq/m³. Below this, no action is required, though there's no known safe threshold. Between 200-600 Bq/m³, remedial action should happen within two years. Above 600 Bq/m³, action should happen within one year. Testing should run at least 3 months, ideally fall or winter when windows are closed and levels are typically highest.

Sub-slab depressurization creates negative pressure beneath the foundation relative to indoor air. A pipe through the slab connects to an inline fan that continuously extracts soil gas and vents it above the roofline. This prevents radon-laden soil gas from entering through slab cracks and penetrations, since air now flows into the soil from the house rather than the reverse. Pressure field extension testing verifies the negative pressure reaches the entire slab area, not just near the extraction point.

Fan sizing depends on required airflow and the static pressure needed to overcome soil resistance, determined mainly by soil permeability. Permeable soils like gravel need higher airflow but lower pressure. Low-permeability clay needs lower airflow but higher static pressure. A single suction point typically covers 465-930 m² in permeable soil but may only extend 90-230 m² in clay, sometimes requiring multiple suction points for larger foundations. Use this calculator to estimate coverage and fan requirements for your specific soil type.

The National Building Code requires a rough-in for future radon mitigation in new residential construction — a passive vent pipe from beneath the slab to outside, capped and ready for a fan if testing later shows elevated radon. This doesn't mean every new home has active mitigation from the start; it means adding a fan later is straightforward if needed. Existing homes without this rough-in require full retrofit installation including slab penetration if testing reveals radon above the Health Canada action level.