#1
Cause of lung cancer in non-smokers
200 Bq/m³
Health Canada action level
<50 Bq/m³
Starlit target level
Radon is a naturally occurring radioactive gas produced by the decay of uranium in soil and rock. It's colourless, odourless, and tasteless — completely undetectable by human senses. Yet according to Health Canada, radon exposure is the leading cause of lung cancer among non-smokers, responsible for approximately 3,200 Canadian deaths annually.
Ontario sits atop geological formations that produce significant radon concentrations. Surveys by Health Canada have found that approximately 7% of Canadian homes exceed the 200 Bq/m³ guideline — but even levels below this threshold carry measurable health risk. The World Health Organization recommends action at 100 Bq/m³.
At Starlit Homes, we don't wait for post-occupancy testing to reveal a problem. Every home we build includes active radon mitigation from day one.
How Radon Enters Your Home
Radon gas migrates upward through soil and enters buildings through any pathway that connects the interior to the ground. In residential construction, the primary entry points are:
Cracks in Foundation Slabs
Even hairline cracks in poured concrete provide sufficient pathways for gas migration. Concrete shrinkage cracking is inevitable — typically appearing within the first year.
Slab-to-Foundation-Wall Joints
The cold joint where the floor slab meets the foundation wall is a primary entry point. Unless specifically sealed with flexible gaskets, this joint allows continuous gas infiltration.
Plumbing & Utility Penetrations
Every pipe, conduit, and drain that penetrates the slab creates a potential pathway. Standard construction rarely seals these penetrations against gas migration.
Sump Pits
Open or poorly sealed sump pits act as direct conduits from the sub-slab gravel bed to the living space — essentially an open pipe to the soil gas.
The driving mechanism is simple: indoor air pressure is typically slightly lower than soil gas pressure beneath the slab (due to stack effect, wind pressures, and exhaust fans). This pressure differential — often as small as 1–5 Pascals — is sufficient to draw radon-laden soil gas continuously into the building.
"In a tight, high-performance home, the pressure differential that drives radon entry can be more consistent than in a leaky house. This is precisely why active mitigation — not just sealing — is essential."
Active Sub-Slab Depressurization: The Gold Standard
The most effective radon mitigation technique for new construction is Active Sub-Slab Depressurization (ASD). The system creates a pressure field beneath the foundation slab that reverses the natural pressure differential, preventing soil gas from entering the building.
The U.S. EPA's Radon-Resistant New Construction guidelines describe ASD as the most reliable and cost-effective approach for new builds. The system consists of:
- Sub-slab aggregate layer: 4" of clean, angular gravel beneath the slab providing a gas-permeable collection field
- Polyethylene vapour barrier: 6-mil poly over the gravel, sealed at all seams and penetrations
- Collection pipe: 4" perforated PVC pipe embedded in the gravel connected to a vertical riser
- Riser pipe: 4" solid PVC running from below-slab through the building to above the roofline
- Inline fan: Low-wattage radon fan mounted in the attic or exterior, creating continuous negative pressure beneath the slab
- Discharge point: Above the roofline, away from windows and air intakes
Integration with Building Performance Systems
Radon mitigation doesn't exist in isolation. It interacts directly with the building's airtightness and ventilation strategies. A home built to our 1.0 ACH standard is tight enough that uncontrolled air infiltration through the slab is minimal — but this also means any radon that does enter is not diluted by accidental ventilation.
This is why our ERV systems and radon mitigation work as complementary strategies. The ERV maintains continuous fresh air exchange and slight positive pressure in the living space, while the ASD system maintains negative pressure beneath the slab. Together, they create a pressure sandwich that keeps soil gases where they belong — underground.
The Starlit Radon Protocol
Standard Radon Mitigation
- 4" clean angular gravel sub-slab drainage/collection layer
- 6-mil polyethylene vapour barrier — taped seams, sealed penetrations
- 4" perforated PVC collection loop in gravel bed
- 4" solid PVC riser through building to above roofline
- RadonAway RP145 inline fan — 60W continuous, 40 dB at 3 ft
- U-tube manometer on riser — visual confirmation of system operation
- All slab penetrations sealed with flexible polyurethane gaskets
- Sump pit sealed with airtight cover and gasketed lid
Target indoor radon: <50 Bq/m³ (75% below Health Canada guideline)
Post-occupancy 90-day alpha-track test: Included with every home
"Installing radon mitigation during construction costs $500–$1,500. Retrofitting the same system after occupancy costs $2,500–$5,000 — and requires invasive work through finished floors and walls."
Key Takeaways
Radon is the #1 cause of lung cancer in non-smokers — colourless, odourless, and present in Ontario soils.
Health Canada's action level is 200 Bq/m³; the WHO recommends 100 Bq/m³; Starlit targets <50 Bq/m³.
Active Sub-Slab Depressurization (ASD) is the gold standard — it reverses the pressure that draws radon in.
Installing during construction costs 60–80% less than retrofitting after occupancy.
ASD works in concert with airtight envelopes and ERV ventilation to create a complete indoor air quality system.
Every Starlit home includes a 90-day post-occupancy radon test to verify system performance.
