The complete step-by-step process — from site assessment and diagnostic testing through installation and post-mitigation verification. Written to the standards Bye Radon follows on every job.
Before any mitigation design begins, the certified professional conducts a systematic inspection of the building. This determines which mitigation methods apply, where suction points should go, and how the system must be routed. A skipped or abbreviated assessment is the most common cause of systems that don't work.
Foundation Type Identification
Every foundation type present in the building must be positively identified — many homes combine two or more, each requiring its own approach.
Foundation Type
Key Features to Document
Poured concrete slab
Sub-slab material (gravel, sand, clay, or tight fill); vapour barrier presence; in-slab HVAC ducts; perimeter drain tile location
Concrete block (CMU) walls
Block core orientation; whether top course is sealed; mortar condition; connection to interior drain tile at footing
Highly porous — usually requires interior barrier membrane with drainage to a sump rather than depressurization
Walk-out / daylight basement
Only the below-grade portion contacts soil; above-grade walls require no radon treatment
Entry Point Survey
Walk the full perimeter of the basement floor and walls and document all visible and probable radon entry points:
The cold joint (perimeter gap between slab and foundation wall) — the primary entry point in most basements
Control joints, saw-cut joints, and expansion joints in the slab
Cracks in the slab or walls — note width, length, and orientation
All pipe and conduit penetrations through slab and walls
Floor drains without a functioning water trap or that connect directly to soil
The sump pit — open, partially covered, or sealed
Exposed soil in utility areas or crawl spaces
The top of hollow CMU walls where cores open to the interior
HVAC System Review
Mechanical systems directly affect building pressurization and radon entry. Document and note:
Furnace combustion type — sealed-combustion (direct-vent) or open-combustion (draws air from the room). Open-combustion is a critical safety constraint for fan sizing.
Whether supply or return ducts are embedded in the concrete slab
Location and capacity of all exhaust fans (bathroom, kitchen, dryer)
HRV or ERV presence and how it is balanced
Safety Note — Open-Combustion Appliances
An improperly sized radon fan can depressurize the building enough to backdraft an open-combustion furnace or water heater, drawing carbon monoxide into the living space. A worst-case depressurization test is mandatory before commissioning any active system in a home with open-combustion appliances.
2Diagnostic Testing — Pressure Field Extension
Pressure Field Extension (PFE) testing — also called sub-slab communication testing — is a mandatory diagnostic step under CAN/CGSB-149.12-2024. It determines whether a proposed suction point can create sufficient negative pressure across the full sub-slab footprint, and provides the data needed to size the fan correctly.
Cannot Be Skipped
Sizing a fan on rule-of-thumb estimates without measuring actual sub-slab conditions violates C-NRPP professional standards. An undersized fan fails to reduce radon. An oversized fan can backdraft combustion appliances, depressurize the building, and cause excess noise and energy costs.
Equipment Required
Micromanometer — minimum resolution 0.1 Pa
Rotary hammer drill with 6 mm masonry bit (diagnostic holes) and 102 mm diamond core bit (permanent suction point)
Vacuum source — shop vac, dedicated test fan, or the permanent radon fan temporarily positioned
Rubber plug fittings for airtight test connections
Smoke pen for airflow visualization at entry points
PFE Procedure
Select the proposed suction point
Choose the most central location in the slab footprint serving the area to be mitigated. If a sump pit or radon rough-in pipe is well-positioned, start there — both are already void spaces with good sub-slab communication.
Drill a test hole at the suction point
Using a 19–25 mm masonry bit, bore through the slab only — stop when you reach sub-slab material. Insert a rubber-plug fitting to create an airtight connection to a vacuum hose.
Apply suction and allow stabilization
Connect the vacuum source and create negative pressure beneath the slab. Allow at least 60 seconds to stabilize before taking readings.
Drill perimeter diagnostic test holes
Using the 6 mm bit, drill 3–5 test holes at the farthest corners and mid-spans of the slab from the suction point.
Measure differential pressure at each test hole
Insert the micromanometer probe into each test hole while suction remains active. Record the reading. A result of at least –1 Pa at the farthest hole confirms adequate communication for that suction point to serve the entire zone.
Assess coverage and permeability
If all perimeter holes show negative pressure (even weakly), one suction point suffices. Any hole reading zero indicates that area is blocked by a footing, wall, or tight fill — an additional suction point is required there. Very high airflow with low pressure differential = coarse gravel (standard fan). Very low airflow with high pressure differential = tight fill (high-static-pressure fan needed, possibly a suction pit required).
Smoke test all entry points
With the test vacuum still active, hold a smoke pen at each suspected entry point (cold joint, cracks, penetrations, drains, sump). Smoke drawn in = active radon pathway that must be sealed. Smoke blown away = positive pressure, not a radon concern.
Fan Selection from PFE Data
Using the measured static pressure at the suction point, pressure at the farthest test hole, approximate airflow, and total pipe length, select a fan from the manufacturer's published performance curve. The goal is to maintain a minimum of –1 Pa across the full sub-slab area during continuous operation. Choose the fan whose curve best matches system resistance — not the largest available "for safety."
3Sealing Radon Entry Points
Sealing alone cannot reduce radon to safe levels and is not a recognized standalone mitigation method under CAN/CGSB-149.12-2024. However, it is a required supporting step — every unsealed opening allows interior air to bypass the sub-slab vacuum zone and reduces system efficiency. Better sealing means the same radon reduction is achievable with a smaller, quieter, longer-lasting fan.
Priority Targets
Cold joint (slab-to-wall perimeter): Highest-priority seal. Use flexible polyurethane or polyurea caulk. Insert closed-cell foam backer rod first in joints wider than 6 mm. Silicone and hydraulic cement alone are not appropriate — they are rigid and will debond as the slab moves seasonally.
Slab cracks: Wire-brush clean, blow out dust, apply polyurethane sealant. For cracks wider than 3 mm, use a backer rod and two-part epoxy or polyurethane injection for full-depth fill.
Pipe and conduit penetrations: Pack gaps over 6 mm with hydraulic cement, then cap with flexible polyurethane sealant. Use non-combustible fire-stop caulk where penetrations pass through fire separations.
Floor drains: If the trap is functional, keep it primed and add an overflow cap. If the drain connects directly to soil, seal it with a mechanical plug or weld plate.
Sump pit: Install a purpose-made gasketed airtight lid with sealed penetrations for the pump discharge and radon suction pipes. Improvised plywood or foam covers are not acceptable.
Realistic Performance Expectation
Sealing alone typically achieves less than 10–15% radon reduction and degrades as sealants age. Its real value is in maximizing active system efficiency — not in replacing it.
4Mitigation Methods by Foundation Type
The method is determined by foundation type and diagnostic results. Homes with more than one foundation type require a combination of approaches applied simultaneously. Active (fan-powered) methods are the only techniques that reliably and sustainably reduce radon to below the Health Canada guideline in most Canadian homes.
Active Sub-Slab Depressurization (ASD)
Primary method — poured concrete slab
ASD is the most widely used and reliable radon mitigation technique in Canada. A motor-driven fan creates a continuous zone of negative pressure in the aggregate or soil layer beneath the concrete slab. Because sub-slab pressure is lower than interior building pressure, radon-laden soil gas is drawn toward the suction point and exhausted outside rather than infiltrating through the floor.
When a sump pit can be sealed airtight, it serves as the ideal suction point — already a void space communicating with the sub-slab drainage zone. In homes with no permeable sub-slab material, the installer mechanically creates a suction pit by chipping out a cavity (typically 150–300 mm diameter, 100–150 mm deep) directly beneath the cored hole.
Typical reduction: 80–95%, commonly bringing levels from several hundred Bq/m³ to below 100 Bq/m³.
Sub-Membrane Depressurization (SMD)
Crawl spaces with exposed earth
A continuous heavy-duty polyethylene membrane (minimum 10-mil; 20-mil preferred) is installed over the entire crawl space floor. All seams are lapped minimum 300 mm and sealed with compatible tape or mastic. All edges are sealed to the foundation walls. One or more suction pipes are placed beneath the membrane before installation — the fan draws radon from beneath the membrane and exhausts it outside.
Every penetration through the membrane — structural posts, plumbing, utility lines — must be individually collared and sealed. A single unsealed penetration short-circuits the pressure field and defeats the system.
Sump Pit Depressurization
Homes with existing sump pits
A purpose-made gasketed airtight lid is installed on the sump pit. The pit communicates with the sub-slab drainage aggregate and, in many homes, with perimeter drain tile — giving the system excellent pressure field extension without requiring any slab coring. The sump pump float, check valve, and discharge pipe all pass through the lid via gasketed, sealed fittings. The cover must be removable for pump service without breaking the suction pipe connection.
Drain Tile / Perimeter Drainage Depressurization
Homes with perimeter drainage systems
Many basements — particularly those built before the 1980s — have a perimeter network of open-joint clay tile or perforated pipe around the footing. These communicate laterally around the full perimeter and can be depressurized from a single access point (a cleanout, the sump connection, or a T-fitting). Especially effective for CMU foundations, where the hollow block cores communicate with the drain tile at the footing level.
Before proceeding: verify the drain tile is not connected to the municipal storm or sanitary sewer. Depressurizing a connected system can draw sewer gases and affect a much larger network than intended.
Hollow Block Wall (CMU) Depressurization
Concrete masonry unit foundation walls
A hole is drilled into a hollow core near the base of the CMU wall and connected to a suction pipe — approximately one suction point per 3–5 linear metres of wall. The top course of CMU blocks must be sealed (with mortar, hydraulic cement, or sealant) before commissioning. If left open, the fan draws conditioned room air down through the top of the wall instead of soil gas from below — the system runs but does nothing for radon.
Heat Recovery Ventilator (HRV) — Dilution Ventilation
Supplementary only — not standalone for high levels
An HRV increases fresh air exchange, diluting accumulated radon. Canadian field studies found a median reduction of approximately 39–43% with continuous HRV operation at high fan speed — meaningful, but rarely sufficient when levels are significantly above 200 Bq/m³. When used for radon control, the HRV must run continuously and be balanced slightly positive (bringing in marginally more air than it exhausts). Do not use exhaust-only ventilation as a radon strategy — sustained exhaust depressurizes the basement relative to the soil and consistently increases radon entry.
5System Installation — Suction Point, Pipe & Fan
Creating the Suction Point
Core through the slab
Use a diamond-tipped core drill to cut a 102 mm (4 inch) hole through the full slab thickness — through the slab only, not deep into sub-slab material.
Excavate the suction pit
Remove sub-slab material to create a cavity approximately 150–300 mm in diameter and 100–150 mm in depth directly beneath the hole. In tight-fill conditions with no granular material, excavate a larger pit (minimum 300 mm diameter, 200 mm deep) and add 19 mm crushed stone to create a collection zone.
Insert the pipe and seal the annular gap
Insert PVC pipe through the core. Pack the annular gap with hydraulic cement on the sub-slab side; seal with flexible polyurethane caulk on the interior side. The seal must be fully airtight — any leak here draws interior room air into the suction pipe instead of sub-slab soil gas.
Pipe Specifications
Parameter
Requirement (CAN/CGSB-149.12-2024)
Material
PVC, Schedule 40 or heavier
Internal diameter
100 mm (4 inch) minimum
Fittings
Solvent-welded PVC throughout — no threaded couplings in enclosed or inaccessible sections
Elbows
Long-radius sweep elbows preferred; each sharp 90° elbow adds ~1.5–2.0 m equivalent pipe resistance
Slope
Minimum 6 mm per linear metre, continuous from suction point toward the fan — no low points that trap condensate
Insulation
Required where pipe passes through unconditioned space (unheated attic, cold room) to prevent condensate from freezing and blocking flow
Labelling
"RADON REDUCTION SYSTEM — DO NOT OBSTRUCT" every 3 m and at every visible change of direction
Fan Placement — Canadian Requirement
In Canada, the radon fan must be located inside the building in a conditioned or semi-conditioned space — typically the basement mechanical room, an enclosed utility space, or a conditioned attic. This differs from US practice where external fan mounting is common. Canadian winters cause external fans to fail from temperature cycling, condensate freeze-up inside the motor, and snow infiltration.
The pipe section between the fan outlet and the discharge point operates under positive pressure. Any joint failure in this section pushes radon-laden soil gas into the building interior. Solvent-weld every joint in the positive-pressure section — no friction or compression fittings.
Fan Installation
Connect the fan housing using manufacturer-specified coupling fittings; verify the airflow arrow points from suction point toward discharge
Install rubber vibration-isolating flexible connectors on both the inlet and outlet sides to prevent mechanical noise from transmitting through the rigid pipe
Mount the fan on a bracket or vibration-isolating pad — do not allow it to hang unsupported from pipe joints
Use only fans manufactured specifically for continuous radon mitigation service — standard HVAC fans are not rated for this application
Multiple Suction Points & Gophering
Where one suction point doesn't achieve full pressure field extension, additional points are required. These can be manifolded to a single fan or assigned individual fans. When manifolding, balance branch resistance so suction is distributed proportionally — a zone with very permeable sub-slab material will draw far more airflow than a tight zone, starving the tight zone of suction.
Gophering extends the collection zone without additional cored holes: using a right-angle masonry bit through the suction hole, short horizontal trenches are created beneath the slab radiating outward from the suction pit, allowing the pressure field to reach areas blocked by tight fill.
6Discharge Point Requirements
The discharge point is where the radon vent pipe terminates to the exterior. A discharge installed too close to a window or air intake will re-introduce radon into the building and negate the entire system.
Clearances (CAN/CGSB-149.12-2024)
Reference Point
Minimum Clearance
Any openable window, door, or operable opening
3.0 m horizontal, or 1.0 m above
Mechanical fresh air intakes (HRV, ERV, HVAC)
1.8 m minimum
Property line
1.8 m minimum
Public sidewalk / pedestrian area
2.1 m above grade
Gas meter or electrical service
1.0 m minimum
Soffit or eave vents
Do not terminate beneath overhangs — exhaust will be drawn into the attic
Sidewall vs. Above-Roof
In Canadian practice, sidewall discharge is preferred. It avoids roof penetrations (which introduce leak risk), keeps the fan in an accessible conditioned space, and performs reliably without freezing issues in cold climates. Above-roof discharge is compliant but requires the termination to extend at minimum 300 mm above the roof surface, be flashed to a watertight standard higher than a standard plumbing vent (the pipe is under positive pressure), and the pipe must be insulated through any unheated attic space.
Termination Fitting
The discharge opening must be fitted with a corrosion-resistant screen or grille — mesh opening 10–12.5 mm. Finer mesh will ice over in Canadian winters and block the system. The screen must be removable for inspection and cleaning. When terminating at a sidewall, use a 180° goose-neck elbow so the opening faces downward, preventing rain, ice, and debris from entering the pipe end.
7System Monitoring Device
Every active radon mitigation system must include a visual performance indicator allowing anyone in the building to confirm — without tools — that the fan is running and the system is under suction. This is a mandatory installation requirement under C-NRPP standards, not optional.
U-Tube Liquid Manometer
The standard device is a U-tube manometer installed on the suction-side pipe (between suction point and fan inlet), in a clearly visible location. When the fan is operating correctly:
The liquid on the suction side sits visibly higher than the open side
The difference in levels indicates suction strength — a healthy reading is typically 0.5–1.75 inWC for most residential systems
If both sides are level, the fan is not operating — the primary failure signal homeowners can identify at a glance
Install the manometer at eye level in the most visible location on the suction-side pipe. Affix the homeowner information decal adjacent to it, showing the baseline reading, what an abnormal reading looks like, and who to call for service.
8Electrical Requirements
All electrical work must comply with the Canadian Electrical Code (CEC) and applicable provincial amendments. New wiring and panel connections require an electrical permit in most provinces and must be performed by a licensed electrician.
Provide a dedicated 120V, 15A receptacle within 1.8 m of the fan — allows future fan replacement without requiring an electrician each time
Where a dedicated receptacle isn't practical, a hardwired connection with an accessible disconnect switch (lockable preferred) within line-of-sight of the fan is acceptable
Do not install the fan on a switched circuit or a circuit that is regularly turned off. If circuit sharing is unavoidable, permanently label the breaker: "RADON FAN — DO NOT SWITCH OFF"
Locate the outlet in a dry area not subject to flooding. If flood risk exists, use a GFCI-protected outlet mounted above the anticipated flood level
9Post-Mitigation Testing & Verification
Installation is not the end of the job. Verification testing confirms the system is working and has achieved the intended radon reduction. There are two required phases.
Phase 1 — Short-Term Verification Test
Run the fan continuously for a minimum of 24 hours before starting the test — the sub-slab pressure field needs time to equilibrate
Test duration: minimum 48 hours
Use a C-NRPP listed short-term test device or a C-NRPP listed continuous radon monitor (CRM)
Place the device in the same location as the original long-term test, or in the lowest occupiable level
Maintain closed-house conditions throughout
What Success Looks Like
A properly designed ASD system reduces radon by 80–95%. If the short-term post-installation result is not substantially lower than the pre-mitigation level, diagnose before signing off: undersized fan, unsealed entry point bypassing the system, a joint leak in the positive-pressure pipe section, or insufficient sub-slab communication requiring an additional suction point.
Ready for a Radon-Free Home?
Bye Radon installs every system to C-NRPP standards. Guaranteed below 100 Bq/m³ — backed by a 5-year warranty.